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C++: A Beginner`s Guide, Second Edition

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1. The output from the program is shown here 5 C A Beginner s Guide by Herbert Schildt Introducing Functions Before call Inside f After call As the output shows f returns to main as soon as the return statement is encountered The second cout statement is never executed Here is a more practical example of return The power function shown in the next program displays the outcome of an integer raised to a positive integer power If the exponent is negative the return statement causes the function to terminate before any attempt is made to compute the result include lt iostream gt using namespace std void power int base int exp int main power 10 2 power 10 2 return 0 Raise an integer to a positive power void power int base int exp int i Return when exp is negative 1f exp lt 0 return Can t do negative exponents i 1 for exp exp i base i cout lt lt The answer is lt lt i The output from the program is shown here The answer is 100 When exp is negative as it is in the second call power returns bypassing the rest of the function A function may contain several return statements As soon as one is encountered the function returns For example this fragment is perfectly valid 6 C A Beginner s Guide by Herbert Schildt void if switchic case a return case b case ca return
2. int j k int amp 1 j independent reference 7 j 10 An independent reference cout lt lt j lt lt lt lt i outputs 10 10 k 121 i k copies k s value into j not k s address cout lt lt n lt lt j Z outputs 121 return Q 12 C A Beginner s Guide by Herbert Schildt This program displays the following output 10 10 121 The address pointed to by a reference variable is fixed it cannot be changed Thus when the statement leak is evaluated it is k s value that is copied into j referred to by i not its address As stated earlier it is generally not a good idea to use independent references because they are not necessary and they tend to garble your code Having two names for the same variable is an inherently confusing situation A Few Restrictions When Using References e There are some restrictions that apply to reference variables e You cannot reference a reference variable e You cannot create arrays of references e You cannot create a pointer to a reference That is you cannot apply the amp operator to a reference Progress Check 1 Cana function return a reference 2 What is an independent reference 3 Can you create a reference to a reference CRITICAL SKILL 6 7 Function Overloading In this section you will learn about one of C s most exciting features function overloading In C two or more functions can share the same name as long as
3. 10 The C standard library is contained in the std namespace 11 No a static member function cannot access the non static data of a class 12 The typeid operator obtains the type of an object at runtime 13 To determine the validity of a polymorphic cast at runtime use dynamic_cast 14 const_cast overrides const or volatile in a cast 43 C A Beginner s Guide by Herbert Schildt Appendix A The Preprocessor The preprocessor is that part of the compiler that performs various text manipulations on your program prior to the actual translation of your source code into object code You can give text manipulation commands to the preprocessor These commands are called preprocessor directives and although not technically part of the C language they expand the scope of its programming environment The preprocessor is a holdover from C and is not as important to C as it is to C Also some preprocessor features have been rendered redundant by newer and better C language elements However since many programmers still use the preprocessor and because it is still part of the C language environment it is briefly discussed here The C preprocessor contains the following directives define error include endif ifndef undef line pragma As is apparent all preprocessor directives begin with a sign Each will be examined here in turn define define is used to define an identifier and a character sequence
4. 1 count lt 100 return if Be aware however that having too many returns can destructure a function and confuse its meaning It is best to use multiple returns only when they help clarify a function Returning Values A function can return a value to its caller Thus a return value is a way to get information out of a function To return a value use the second form of the return statement shown here return value Here value is the value being returned This form of the return statement can be used only with functions that do not return void A function that returns a value must specify the type of that value The return type must be compatible with the type of data used in the return statement If it isn t a compile time error will result A function can be declared to return any valid C data type except that a function cannot return an array To illustrate the process of functions returning values the box function can be rewritten as shown here In this version box returns the volume Notice that the placement of the function on the right side of an assignment statement assigns the return value to a variable 7 C A Beginner s Guide by Herbert Schildt Returning a value include lt iostream gt using namespace std int box int length int width int height return the volume int main The return value from bex int answer is assigned to answer answer box 10 11 3 a
5. Herbert Schildt Module 1 C Fundamentals Table of Contents CRITICAL SKILL 1 1 A Brief History of C CRITICAL SKILL 1 2 How C Relates to Java and C CRITICAL SKILL 1 3 Object Oriented Programming CRITICAL SKILL 1 4 A First Simple Program CRITICAL SKILL 1 5 A Second Simple Program CRITICAL SKILL 1 6 Using an Operator CRITICAL SKILL 1 7 Reading Input from the Keyboard Project 1 1 Converting Feet to Meters CRITICAL SKILL 1 8 Two Control Statements CRITICAL SKILL 1 9 Using Blocks of Code Project 1 2 Generating a Table of Feet to Meter Conversions CRITICAL SKILL 1 10 Introducing Functions CRITICAL SKILL 1 11 The C Keywords CRITICAL SKILL 1 12 Identifiers If there is one language that defines the essence of programming today it is C It is the preeminent language for the development of high performance software Its syntax has become the standard for professional programming languages and its design philosophy reverberates throughout computing 1 C A Beginner s Guide by Herbert Schildt C is also the language from which both Java and C are derived Simply stated to be a professional programmer implies competency in C It is the gateway to all of modern programming The purpose of this module is to introduce C including its history its design philosophy and several of its most important features By far the hardest thing about learning a programming language is the fact that no elem
6. Implement MyClass constructor MyClass MyClass 16 C A Beginner s Guide by Herbert Schildt cout lt lt Destructing n This destructor simply displays a message but in real programs the destructor would be used to release one or more resources such as a file handle or memory used by the class Progress Check 1 What is a constructor and when is it executed 2 Does a constructor have a return type 3 When is a destructor called CRITICAL SKILL 8 5 Parameterized Constructors In the preceding example a parameterless constructor was used While this is fine for some situations most often you will need a constructor that has one or more parameters Parameters are added to a constructor in the same way that they are added to a function just declare them inside the parentheses after the constructor s name For example here is a parameterized constructor for MyClass Myclass MyClass int i x i To pass an argument to the constructor you must associate the value or values being passed with an object when it is being declared C provides two ways to do this The first method is illustrated here MyClass ob1 MyClass 101 This declaration creates a MyClass object called ob1 and passes the value 101 to it However this form is seldom used in this context because the second method is shorter and more to the point In the second method the argument or arguments must follow the object s name
7. include lt iostream gt using namespace std int main int x for x 0 x 123 No increment expression cout lt lt Enter a number cin gt gt x return 0 16 C A Beginner s Guide by Herbert Schildt Here the increment portion of the for definition is blank This means that each time the loop repeats x is tested to see whether it equals 123 but no further action takes place If however you type 123 at the keyboard the loop condition becomes false and the loop exits The for loop will not modify the loop control variable if no increment portion of the loop is present Another variation on the for is to move the initialization section outside of the loop as shown in this fragment x 0 x is initialized outside the loop for m lt 10 cout lt lt Xx lt lt F Here the initialization section has been left blank and x is initialized before the loop is entered Placing the initialization outside of the loop is generally done only when the initial value is derived through a complex process that does not lend itself to containment inside the for statement Notice that in this example the increment portion of the for is located inside the body of the loop The Infinite for Loop You can create an infinite loop a loop that never terminates using this for construct LOL ys re This loop will run forever Although there are some programming tasks
8. 34 000 000 miles lightspeed 186000 0 186 000 per second To compute the delay divide distance by lightspeed This yields the delay in seconds Assign this value to delay and display the results These steps are shown here delay distance lightspeed cout lt lt Time delay when talking to Mars lt lt delay lt lt seconds n Divide the number of seconds in delay by 60 to obtain the delay in minutes display that result using these lines of code delay in min delay 60 0 Here is the entire Mars cpp program listing Project 2 1 Talking to Mars oy include lt iostream gt using namespace std int main double distance double lightspeed double delay double delay in min distance 34000000 0 34 000 000 miles lightspeed 186000 0 186 000 per second delay distance lightspeed cout lt lt Time delay when talking to Mars lt lt delay lt lt seconds n delay in min delay 60 0 Counc lt lt Ihas 19 lt lt delay an min lt lt T minutes 11 C A Beginner s Guide by Herbert Schildt return 0 7 Compile and run the program The following result is displayed Time delay when talking to Mars 182 796 seconds This 1s 3 04659 minutes 8 On your own display the time delay that would occur in a bidirectional conversation with Mars CRITICAL SKILL 2 2 Literals Literals refer to fixed human readable values that cannot be altered by
9. LE 0 n tl area n t2 areal n t3 area Here is the output from this version Initio ior Gl Triangle is right Width and height are 8 and 12 is 48 LOr EZ is 48 Or eo 18 Area Info Area Info getHeight lt lt style lt lt 12 0 lt lt cc ac ay yn a yE m n ji n i Ff Triangle is right Width and height are 8 and 12 Triangle is isosceles Width and height are 4 and 4 C A Beginner s Guide by Herbert Schildt Area is 8 Progress Check 1 How does a derived class execute its base class constructor Can parameters be passed to a base class constructor 3 What constructor is responsible for initializing the base class portion of a derived object the one defined by the derived class or the one defined by the base class Extending the Vehicle Class This project creates a subclass of the Vehicle class first developed in Module 8 As you should recall Vehicle encapsulates information about vehicles including the number of passengers they can carry their fuel capacity and their fuel consumption rate We can use the Vehicle class as a Starting point from which more specialized classes are developed For example one type of vehicle is a truck An important attribute of a truck is its cargo capacity Thus to create a Truck class you can inherit Vehicle adding an instance variable that stores the carrying capacity
10. When including a file whether the filename is enclosed by quotes or angle brackets determines how the search for the specified file is conducted If the filename is enclosed between angle brackets the compiler searches for it in one or more implementation defined directories If the filename is enclosed between quotes then the compiler searches for it in some other implementation defined directory which is typically the current working directory If the file is not found in this directory the search is restarted as if the filename had been enclosed between angle brackets Since the search path is implementation defined you will need to check your compiler s user manual for details Conditional Compilation Directives There are several directives that allow you to selectively compile portions of your program s source code This process called conditional compilation is widely used by commercial software houses that provide and maintain many customized versions of one program Hif Helse elif and endif The general idea behind the if directive is that if the constant expression following the if is true then the code between it and an endif will be compiled otherwise the code will be skipped over endif is used to mark the end of an if block The general form of if is if constant expression statement sequence Hendif 5 C A Beginner s Guide by Herbert Schildt If the constant expression is true the block of code
11. b false cout lt lt bis lt lt b lt lt n b true cout lt lt b is lt lt b lt lt n i F Ji a bool value can control the if statement ifib cout lt lt This is executed n b false ee i A single bool valve can ifib cout lt lt This is not executed n t control an if statement ji outcome of a relational operator is a true false value cout lt lt 10 gt 9 is lt lt 10 gt 9 lt lt An F return U The output generated by this program is shown here B i5 U b is 1 This is executed Ol gt Oo aio 1 There are three interesting things to notice about this program First as you can see when a bool value is output using cout O or 1 is displayed As you will see later in this book there is an output option that causes the words false and true to be displayed Second the value of a bool variable is sufficient by itself to control the if statement There is no need to write an if statement like this if b true 9 C A Beginner s Guide by Herbert Schildt Third the outcome of a relational operator such as lt is a Boolean value This is why the expression 10 gt 9 displays the value 1 Further the extra set of parentheses around 10 gt 9 is necessary because the lt lt operator has a higher precedence than the gt void The void type specifies a valueless expression This probably seems strange now but you will see h
12. cin gt gt word J 0 i i strcmp dictionary i 0 word 1 cout lt lt dictionary i 1 lt lt n break To find a definition word is searched for in dictionary If a match is found the definition is displayed for i 0 dictionary i 1 dictionary i 0 cout lt lt word lt lt not found n return 0 Here is asample run Enter word network An interconnected group of computers When the array dictionary is created it is initialized with a set of words and their meanings Recall C stores all string constants in the string table associated with your program so the array need only store pointers to the strings The program works by testing the word entered by the user against the strings stored in the dictionary If a match is found the meaning is displayed If no match is found an error message is printed Notice that dictionary ends with two null strings These mark the end of the array Recall that a null string contains only the terminating null character The for loop runs until the first character in a string is null This condition is tested with this expression dictionary i 0 The array indices specify a pointer to a string The obtains the character at that location If this character is null then the expression is false and the loop terminates Otherwise the expression is true and the loop continues The Null Pointer Convention After a pointer is declared
13. include lt iostream gt using namespace std int negate const int val int main int result int v 10 result negate amp v cout lt lt v lt lt negated is lt lt result cout lt lt n return 0 int negate const int val This specifies val as a const pointer return val Since val is declared as being a const pointer the function can make no changes to the value pointed to by val Since negate does not attempt to change val the program compiles and runs correctly However if negate were written as shown in the next example a compile time error would result This won t work int negate const int val val val Error can t change return val In this case the program attempts to alter the value of the variable pointed to by val which is prevented because val is declared as const The const modifier can also be used on reference parameters to prevent a function from modifying the object referenced by a parameter For example the following version of negate is incorrect because it attempts to modify the variable referred to by val 3 C A Beginner s Guide by Herbert Schildt This won t work either int negate const int amp val val val Error can t change return val volatile The volatile modifier tells the compiler that a variable s value may be changed in ways not explicitly specified by the program For exampl
14. 36 C A Beginner s Guide by Herbert Schildt while items i lt x amp amp i lt right i while x lt items j amp amp j gt left j if i lt j f y items i items i items j items j y i j while i lt 4 1f left lt j gqs items left j 1f 1 lt right qs items i right This function must be called with the indices of the region to be sorted The left parameter must contain the beginning left boundary of the partition The right parameter must contain the ending right boundary of the partition When first called the partition represents the entire array Each recursive call progressively sorts a smaller partition 4 To use the Quicksort simply call quicksort with the name of the array to be sorted and its length After the call returns the array will be sorted Remember this version works only for character arrays but you can adapt the logic to sort any type of arrays you want 5 Here is a program that demonstrates the Quicksort i Project 5 1 A version of the Quicksort for sorting characters a J include lt iostream gt include lt cstring gt using namespace std void quicksort char items int len void qs char items int left int right int main char str jfmckldoelazlkper cout lt lt Original order lt lt str lt lt n 37 C A Beginner s Guide by Herbert Schildt quicksort str strlen str cout
15. 6 When using strcat how large must the recipient array be 7 In a multidimensional array how is each index specified 8 Show how to initialize an int array called nums with the values 5 66 and 88 9 What is the principal advantage of an unsized array declaration 10 What is a pointer What are the two pointer operators 11 Can a pointer be indexed like an array Can an array be accessed through a pointer 12 Write a program that counts the uppercase letters in a string Have it display the result 13 What is it called when one pointer points to another pointer 14 Of what significance is a null pointer in C 42 C A Beginner s Guide by Herbert Schildt Module 5 Introducing Functions Table of Contents CRITICAL SKILL 5 1 Know the general form of a function CRITICAL SKILL 5 2 Creating a Function CRITICAL SKILL 5 3 Using Arguments CRITICAL SKILL 5 4 Using return CRITICAL SKILL 5 5 Using Functions in Expressions CRITICAL SKILL 5 6 Local Scope CRITICAL SKILL 5 7 Global Scope CRITICAL SKILL 5 8 Passing Pointers and Arrays to Functions CRITICAL SKILL 5 9 Returning Pointers CRITICAL SKILL 5 10 Pass Command Line Arguments to main CRITICAL SKILL 5 11 Function Prototypes CRITICAL SKILL 5 12 Recursion This module begins an in depth discussion of the function Functions are the building blocks of C and a firm understanding of them is fundamental to becoming a successful C programmer Here you
16. Although most compilers will continue to support the default to int rule for the sake of backward compatibility you should explicitly specify the return type of every function that you write Since older code frequently made use of the default integer return type this change is also something to keep in mind when converting legacy code Module 5 Mastery Check 1 Show the general form of a function 2 Create a function called hypot that computes the length of the hypotenuse of a right triangle given the lengths of the two opposing sides Demonstrate its use in a program For this problem you will need to use the sart standard library function which returns the square root of its argument It has this prototype double sqrt double val It uses the header lt cmath gt 3 Cana function return a pointer Can a function return an array 4 Create your own version of the standard library function strlen Call your version mystrlen and demonstrate its use in a program 5 Doesa local variable maintain its value between calls to the function in which it is declared 6 Give one benefit of global variables Give one disadvantage 7 Create a function called byThrees that returns a series of numbers with each value 3 greater than the preceding one Have the series start at 0 Thus the first five numbers returned by byThrees are O 3 6 9 and 12 Create another function called reset that causes byThrees to s
17. Determine if one set is a superset of another bool Set operator Set ob2 1f len lt ob2 1len return false obl has fewer elements for int i 0 i lt ob2 len i i1f find ob2 members i 1 return false return true 11 Set intersection Set Set operator amp Set ob2 Set newset Add elements common to both sets for int 1 0 i lt len i if ob2 find members 1i 1 add if element in both sets newset newset members il return newset return set Module 10 Inheritance Virtual Functions and Polymorphism 1 Aclass that is inherited is called a base class The class that does the inheriting is called a derived class 2 A base class does not have access to the members of derived classes because a base class has no knowledge of derived classes A derived class does have access to the non private members of its base class es 30 C A Beginner s Guide by Herbert Schildt A circle class class Circle public TwoDShape public Circle double r TwoDShape r specify radius double area return getWidth getWidth 3 1416 hi 4 To prevent a derived class from having access to a member of a base class declare that member as private in the base class 5 Here is the general form of a derived class constructor that calls a base class constructor derived class base class 6 Constructors are always called in order of derivation
18. Inside normal constructor Inside copy constructor 10 Destructing copy 1 Destructing original 15 when a is passed to display C A Beginner s Guide by Herbert Schildt Here is what occurs when the program is run When a is created inside main the value of its copynumber is set to 0 by the normal constructor Next a is passed to ob of display When this occurs the copy constructor is called and a copy of a is created In the process the copy constructor increments the value of copynumber When display returns ob goes out of scope This causes its destructor to be called Finally when main returns a goes out of scope You might want to try experimenting with the preceding program a bit For example create a function that returns a MyClass object and observe when the copy constructor is called Progress Check 1 When the default copy constructor is used how is a copy of an object made 2 A copy constructor is called when one object is assigned to another True or false 3 Why might you need to explicitly define a copy constructor for a class CRITICAL SKILL 9 6 Friend Functions In general only other members of a class have access to the private members of the class However it is possible to allow a nonmember function access to the private members of a class by declaring it as a friend of the class To make a function a friend of a class you include its prototype in the public section of the class
19. Leftt rotate each letter by a value derived from the key string rotnum key i3klen 8 msg i lrotate msg i rotnum cout lt lt Encoded message lt lt msg lt lt n Decode the message by right rotating for int i 0 i lt strlen msg i Right rotate each letter by a value derived from the key string rotnum key iSklen amp 8 msg i rrotate msg 1i rotnum cout lt lt Decoded message lt lt msg lt lt n return OQ 71 C A Beginner s Guide by Herbert Schildt 22 Lett rotate a byte n places unsigned char lrotate unsigned char val int n unsigned int t t val for int i 0 i lt n i t t lt 1 Tf a bit shifts out it will be in bit 8 of the integer t If this is the case put that bit on the right side 1f t amp 256 t t 1 put a 1 on the right end return t return the lower 8 bits C A Beginner s Guide by Herbert Schildt Right rotate a byte n places unsigned char rrotate unsigned char val int n i unsigned int t t val First move the value 8 bits higher t t lt lt amp for int i 0 i lt n i t t gt gt 1 I a bit shifts out it will be in bit 7 of the integer t If this is the case put that bit on the left side 1f t amp 128 t t 32768 put a 1 on left end Finally move the result back to the lower 8 bits of t t t gt
20. The final way that num can be declared is as a pointer This is the method most commonly used in professionally written C programs Here is an example 21 C A Beginner s Guide by Herbert Schildt void display int num Parameter declared as a pointer int i for i 0 i lt 10 i cout lt lt num i lt lt The reason void cube int n int num itis possible to declare while num n n n n This changes the value of the array num as a num element pointed to by n pointer is nites that any pointer can be indexed using as if it were an array Recognize that all three methods of declaring an array parameter yield the same result a pointer It is important to remember that when an array is used as a function argument its address is passed to a function This means that the code inside the function will be operating on and potentially altering the actual contents of the array used to call the function For example in the following program examine the function cube which converts the value of each element in an array into its cube To call cube pass the address of the array as the first argument and the size of the array as the second Change the contents of an array using a function include lt iostream gt using namespace std void cube int n int num int main int i nums 10 for i 0 1 lt 10 i nums i i l cout lt lt Original contents
21. Use static to count function invocations 19 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std int counter int main int result for int i 0 i lt 10 i result counter cout lt lt Function called lt lt result lt lt times lt lt n return 0 int counter static count 0 count return count Specifying x as register will have the most impact on performance followed by y and then z The reason is that x is accessed most frequently within the loop y the second most and z is used only when the loop is initialized The amp is a bitwise operator that acts on the individual bits within a value amp amp is a logical operator that acts on true false values The statement multiplies the current value of x by 10 and assigns that result to x It is the same as xX x 10 Use rotations to encode a message 20 C A Beginner s Guide by Herbert Schildt include lt iostream gt include lt cstring gt using namespace std unsigned char rrotate unsigned char val int n unsigned char lrotate unsigned char val int n void show_binary unsigned int u int main char msg This is a test char key xanadu int klen strlen key int rotnum cout lt lt Original message lt lt msg lt lt n Encode the message by left rotating for int i 0 i lt strlen msg i
22. function to QType as shown here i Put a data into the queue void put OType data if putloc size cout lt lt Queue is full n return put loc q putloc data 5 Change the return type of get to QType as shown next Get data from the queue OType get d 1f getloc putloc cout lt lt Queue is empty n return 0 getloc return q getloc 6 The entire generic Queue class is shown here along with a main function to demonstrate its use Project 12 1 A template queue class y include lt iostream gt using namespace std const int maxQOsize 100 This creates a generic queue class template lt class OType gt class Queue OType q maxQOsize this array holds the queue int size Maximum number of elements that the queue can store int putloc getloc the put and get indices public Construct a queue of a specific length Queue int len Queue must be less than max and positive 1f len gt maxQOsize len maxQsize else if len lt 0 len 1 24 C A Beginner s Guide by Herbert Schildt 25 size len putloc getloc 0 Put data into the queue wold put QOType data 1f putloc size cout lt lt Queue is full n return putloc q putloc data Get data from the queue OQType get 1f getloc putloc cout lt lt Queue is empty n return QO get
23. i nums looks like this nums O nums 1 nums 2 nums 3 nums 4 ERS EEE Arrays are common in programming because they let you deal easily with sets of related variables Here is an example The following program creates an array of ten elements and assigns each element a value It then computes the average of those values and finds the minimum and the maximum value 3 C A Beginner s Guide by Herbert Schildt i Compute the average and find the minimum and maximum of a set of values a include lt iostream gt using namespace std int main int i avg min_val max_val int nums 10 nums 0 10 nums 1 18 nums 2 75 nums 3 0 nums 4 1 nums 5 56 nums 6 100 numas 7 12 numas 8 19 nums 9 88 compute the average avg 0 for i 0 i lt 10 i avg nums i Sum the values in nums avg 10 4 Calculate the average LE l l cout lt lt Average is lt lt avg lt lt n Eind minimum and maximum values min val max_val nums 0 Find the minimum and for i 1 i lt 10 i maximum values in nums if nums i lt min_val min wal nums i 1f nums i gt max_val max val nums i cout lt lt Minimum value lt lt min val lt lt n cout lt lt Maximum value lt lt max val lt lt n return O The output from the program is shown here Average is 34 Minimum valu
24. lt a lt lt lt b lt lt n calls explicitly overloaded swapargs calls generic swapargs calls generic swapargs This calls the explicit overload of swapargs cout lt lt Swapped i j lt lt i lt lt lt lt j lt lt n cout lt lt Swapped x y lt lt x lt lt lt lt y lt lt n cout lt lt Swapped a b return OQ lt lt a lt lt lt b lt lt n This program displays the following output Original i J 10 Original x y 10 Original a D x Z 20 1 23 3 Inside swapargs int specialization Inside template swapargs Inside template swapargs Swapped i J 20 10 Swapped x y 23 3 Swapped a b Z X 18 10 1 C A Beginner s Guide by Herbert Schildt As the comments inside the program indicate when swapargs i j is called it invokes the explicitly overloaded version of swapargs defined in the program Thus the compiler does not generate this version of the generic swapargs function because the generic function is overridden by the explicit overloading Relatively recently an alternative syntax was introduced to denote the explicit specialization of a function This newer approach uses the template keyword For example using the newer specialization syntax the overloaded swapargs function from the preceding program looks like this Use the newer style specialization syntax template lt g
25. strepy style str _ hitidlize style which double area return getWidth getHeight 2 void showsStyle cout lt lt Triangle is lt lt style lt lt is specific to Triangle Here Triangle s constructor initializes the members of TwoDShape that it inherits along with its own style field 13 C A Beginner s Guide by Herbert Schildt When both the base class and the derived class define constructors the process is a bit more complicated because both the base class and derived class constructors must be executed CRITICAL SKILL 10 4 Calling Base Class Constructors When a base class has a constructor the derived class must explicitly call it to initialize the base class portion of the object A derived class can call a constructor defined by its base class by using an expanded form of the derived class constructor declaration The general form of this expanded declaration is shown here derived constructor arg list base cons arg list body of derived constructor Here base cons is the name of the base class inherited by the derived class Notice that a colon separates the constructor declaration of the derived class from the base class constructor If a class inherits more than one base class then the base class constructors are separated from each other by commas The following program shows how to pass arguments to a base class constructor It defines
26. 1 is lt lt i lt lt n Here are the three different implementations of f void int i int j cout lt lt In f int int iis lt lt i cout lt lt j is lt lt j lt lt n void f double k cout lt lt In f double k is lt lt k lt lt n This program produces the following output In f int i is 10 In fiint int iis 10 j is 20 In E double k is 12 23 As you can see f is overloaded three times The first version takes one integer parameter the second version requires two integer parameters and the third version has one double parameter Because the parameter list for each version is different the compiler is able to call the correct version of each function based on the type of the arguments specified at the time of the call To understand the value of function overloading consider a function called neg that returns the negation of its arguments For example when called with the value 10 neg returns 10 When called with 9 it returns 9 Without 14 C A Beginner s Guide by Herbert Schildt function overloading if you wanted to create negation functions for data of type int double and long you would need three different functions each with a different name such as ineg Ineg and fneg However through the use of function overloading you can use one name such as neg to refer to all functions that return the negation o
27. Using smallQ to generate errors n Now use smallQ to generate some errors for i 0 i lt 5 i cout lt lt Attempting to store lt lt char B 1 eamallO put Z i cout lt lt n cout lt lt n 30 f C A Beginner s Guide by Herbert Schildt more errors on smallQ cout lt lt for i 0C 1f ch cout lt lt Contents of smallQ H i lt 5 1 ch smallQ get 0 cout lt lt ch 7 The output produced by the program is shown here Using bigQ to store the alphabet Contents of bigQ ABCDEFGHIJKLMNOPORSTUVWXYZ Using smallQ to generate errors Attempting Attempting Attempting Attempting Attempting Co tO tO tO tO store store store store store Contents of smallQ qganxkKN Queue is full ZYXW Queue is empty 8 On your own try modifying Queue so that it stores other types of objects For example have it store ints or doubles CRITICAL SKILL 8 7 Arrays of Objects You can create arrays of objects in the same way that you create arrays of any other data type For example the following program creates an array of MyClass objects The objects that comprise the elements of the array are accessed using the normal array indexing syntax 31 C A Beginner s Guide by Herbert Schildt Create an array of objects include lt iostream gt using namespace std class MyClass int x pu
28. Width and height are lt lt width lt lt and lt lt height lt lt n accessor functions double getWidth return width double getHeight return height void setWidth double w width w void setHeight double h height h ti Triangle is derived from TwoDShape class Triangle public TwoDShape char style 20 now private public Various TwoDShape constructors A default constructor This automatically invokes the default constructor of TwoDShape Triangle strepy style unknown Constructor with three parameters Triangle char str double w double h TwoDShape w h strepy style str Construct an isosceles triangle Triangle double x TwoDShape x strcpy style isosceles 17 Various Triangle constructors C A Beginner s Guide by Herbert Schildt double area return getWidth void showStyle cout lt lt 7 int main Triangle Triangle Triangle t1 C2 cout lt lt Triangle is tl t2 right 8B t3a 4 0 Info for tl tl showstyle E1l showDim cout lt lt cout lt lt cout lt lt Area is 7 lt lt n EL 1 Info for tid t2 showStyle t2 showDim cout lt lt Area is lt lt cout lt lt n cout lt lt Info for t3 t3 showStyle t3 showDim cout lt lt Area is lt lt cout lt lt n return 0
29. for ThreeD ThreeD temp temp x xX op2 x These are integer additions temp y y op2 y and the retains its original temp z z op2 z meaning relative to them return temp mM Return a new object Leave arguments unchanged Overload assignment ThreeD ThreeD operator ThreeD op2 Overload for ThreeD xXx op2 x These are integer assignments op2 y and the retains its original a S coe vi a Return the modified object Z op2 z meaning relative to them return A ol aa 29 C A Beginner s Guide by Herbert Schildt Show X Y Z coordinates void ThreeD show cout lt lt x lt lt p ri cout lt lt y lt lt cout lt lt z lt lt n int main ThreeD a l 2 3 b 10 10 10 c ri cout lt lt Original value of a a show cout lt lt Original value of b b show cout lt lt An c a b add a and b together cout lt lt Value of c after c a b c show cout lt lt n r c a b c adda b and ce together cout lt lt Value of c after c a b c c show Colt oc m n c be as cout lt lt Value of c after c b as c show cout lt lt Value of b after c b as b show return This program produces the following output demonstrate multiple assignment r F M y F Original value of a 1 2 3 Original value o
30. math functions All C compilers support these functions and their descriptions will be found in your compiler s documentation They all require the header lt cmath gt The condition controlling the loop may be any valid C expression It does not need to involve the loop control variable In the next example the loop continues to execute until the rand function produces a value greater than 20 000 Loop until a random number that is greater than 20 000 15 C A Beginner s Guide by Herbert Schildt include lt iostream gt include lt cestdlib gt using namespace std int main int i int r r rand for i 0 r lt 20000 i This conditional expression does not use r rand the loop control variable cout lt lt Number is lt lt r lt lt It was generated on try lt lt 1 lt lt return 0 Here is a sample run Number is 26500 It was generated on try 3 Each time through the loop a new random number is obtained by calling rand When a value greater than 20 000 is generated the loop condition becomes false terminating the loop Missing Pieces Another aspect of the for loop that is different in C than in many computer languages is that pieces of the loop definition need not be there For example if you want to write a loop that runs until the number 123 is typed in at the keyboard it could look like this A for loop with no increment
31. return For example if the program is called ComLine then executing it like this C gt ComLine one two three causes the following output ComLine one two three C does not stipulate the exact nature of a command line argument because host environments operating systems vary considerably on this point However the most common convention is as follows each command line argument must be separated by spaces or tabs Often commas semicolons and the like are not valid argument separators For example one two and three is made up of four strings while One two and three has two strings the comma is not a legal separator 27 C A Beginner s Guide by Herbert Schildt If you need to pass a command line argument that does in fact contain spaces then you must place it between quotes For example this will be treated as a single command line argument this is one argument Keep in mind that the examples provided here apply to a wide variety of environments but not necessarily to yours Usually you will use argc and argv to get initial options or values such as a filename into your program In C you can have as many command line arguments as the operating system will allow Using command line arguments will give your program a professional appearance and facilitate the program s use in batch files Passing Numeric Command Line Arguments When you pass numeric data as a command line argument to a program
32. y b T div return x y Create a specific instance int main of a generic class Create a version of MyClass for doubles MyClass lt double gt d_ob 10 0 3 0 cout lt lt double division lt lt d_ob div lt lt n Create a version of MyClass for ints MyClass lt int gt i_ob 10 3 cout lt lt integer division lt lt i_ob div lt lt n return OQ The output is shown here double division 331 35535 20 C A Beginner s Guide by Herbert Schildt integer division 3 As the output shows the double object performed a floating point division and the int object performed an integer division When a specific instance of MyClass is declared the compiler automatically generates versions of the div function and x and y variables necessary for handling the actual data In this example two different types of objects are declared The first d_ob operates on double data This means that x and y are double values and the outcome of the division and the return type of div is double The second i_ob operates on type int Thus x y and the return type of div are int Pay special attention to these declarations Exceptions Templates and Other Advanced Topics MyClass lt double gt d_ob 10 0 3 0 MyClass lt int gt i_ob 10 3 Notice how the desired data type is passed inside the angle brackets By changing the type of data specified when MyClass objects ar
33. 1 What is a null terminated string 2 To hold a string that is 8 characters long how long must the character array be 3 What function can be used to read a string containing spaces from the keyboard CRITICAL SKILL 4 5 Some String Library Functions C supports a wide range of string manipulation functions The most common are strcepy Strcac strcmp strlen 13 C A Beginner s Guide by Herbert Schildt The string functions all use the same header lt cstring gt Let s take a look at these functions now strcpy A call to strcpy takes this general form strcpy to from The strcpy function copies the contents of the string from into to Remember the array that forms to must be large enough to hold the string contained in from If it isn t the to array will be overrun which will probably crash your program strcat A call to strcat takes this form strcat s1 s2 The strcat function appends s2 to the end of s1 s2 is unchanged You must ensure that s1 is large enough to hold its original contents and those of s2 strcmp A call to strcmp takes this general form strcmp si s2 The strcmp function compares two strings and returns 0 if they are equal If s1 is greater than s2 lexicographically that is according to dictionary order then a positive number is returned if it is less than s2 a negative number is returned The key to using strcmp is to remember that it returns
34. 12 13 A cast is an explicit type conversion 14 Here is one way to find the primes between 1 and 100 There are of course other solutions Find prime numbers between 1 and 100 include lt iostream gt using namespace std int main int i j bool isprime for i l i lt 100 i isprime true see if the number is evenly divisible for j 2 J lt 1 2 J it is then it is not prime 1 1 3 0 isprime false if isprime cout lt lt i lt lt is prime n return 0 Module 3 Program Control Statements 1 Count periods 4 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std int main char ch int periods 0 cout lt lt Enter a to stop n do cin gt gt ch 1f ch periods while ch cout lt lt Periods lt lt periods lt lt n return 0 2 Yes If there is no break statement concluding a case sequence then execution will continue on into the next case A break statement prevents this from happening if condition statement else if condition Statement else if condition statement else statement 4 The last else associates with the outer if which is the nearest if at the same level as the else 5 for int i 1000 i gt 0 i 2 6 No According to the ANSI ISO C Standard i is not known outside of the for loop in which it is declared No
35. Different types of exceptions can be caught void Xhandler int test try if test throw test throw int else throw Value is zero throw char catch int 1 i This catches int exceptions cout lt lt Caught One Ex lt lt i lt lt n catch char str ac This catches char exceptions cout lt lt Caught a string cout lt lt str lt lt n 7 C A Beginner s Guide by Herbert Schildt int main cout lt lt start n Shandler Shandler Ahandler Ahandler i Je 1 2 0 3 F cout lt lt end return OQ In general catch expressions are checked in the order in which they occur in a program Only a matching statement is executed All other catch blocks are ignored Catching Base Class Exceptions There is one important point about multiple catch statements that relates to derived classes A catch clause for a base class will also match any class derived from that base Thus if you want to catch exceptions of both a base class type and a derived class type put the derived class first in the catch sequence If you don t the base class catch will also catch all derived classes For example consider the following program g C A Beginner s Guide by Herbert Schildt Catching derived classes This program is wrong include lt iostream gt using namespace std class E f F class D public B int mair D
36. Here is asample run Help on 1s 1E 2 switch Choose one 1 The if if condition statement else statement CRITICAL SKILL 3 3 The for Loop You have been using a simple form of the for loop since Module 1 You might be surprised at just how powerful and flexible the for loop is Let s begin by reviewing the basics starting with the most traditional forms of the for The general form of the for loop for repeating a single statement is for initialization expression increment For repeating a block the general form is for initialization expression increment statement sequence 13 statement C A Beginner s Guide by Herbert Schildt The initialization is usually an assignment statement that sets the initial value of the loop control variable which acts as the counter that controls the loop The expression is a conditional expression that determines whether the loop will repeat The increment defines the amount by which the loop control variable will change each time the loop is repeated Notice that these three major sections of the loop must be separated by semicolons The for loop will continue to execute as long as the conditional expression tests true Once the condition becomes false the loop will exit and program execution will resume on the statement following the for block The following program uses a for loop to print the square roots of the numbers between 1 and 99 Notice that in this
37. If it follows its operand the operator int notused function is called This same approach is also used to overload the prefix and postfix decrement operator relative to any class You might want to try defining the decrement operator relative to ThreeD as an exercise As a point of interest early versions of C did not distinguish between the prefix and postfix forms of the increment or decrement operators For these old versions the prefix form of the operator function was Called for both uses of the operator When working on older C code be aware of this possibility Progress Check 1 Operators must be overloaded relative to a class True or false 2 How many parameters does a member operator function have for a binary operator 3 Fora binary member operator function the left operand is passed via CRITICAL SKILL 9 11 Nonmember Operator Functions You can overload an operator for a class by using a nonmember function which is often a friend of the class As you learned earlier friend functions do not have a this pointer Therefore when a friend is used to overload an operator both operands are passed explicitly when a binary operator is overloaded and one operand is passed explicitly when a unary operator is overloaded The only operators that cannot be overloaded using friend functions are and gt The following program uses a friend instead of a member function to overload the operator for the ThreeD cla
38. In all cases when typeid is applied to a pointer of a non polymorphic class hierarchy then the base type of the pointer is obtained That is no determination of what that pointer is actually pointing to is made As an experiment comment out the virtual function f in Base and observe the results As you will see the type of each object will be Base because that is the type of the pointer Since typeid is commonly applied to a dereferenced pointer that is one to which the operator has been applied a special exception has been created to handle the situation in which the pointer being dereferenced is null In this case typeid throws a bad_typeid exception References to an object of a polymorphic class hierarchy work the same as pointers When typeid is applied to a reference to an object of a polymorphic class it will return the type of the object actually being referred to which may be of a derived type The circumstance where you will most often make use of this feature is when objects are passed to functions by reference There is a second form of typeid that takes a type name as its argument This form is shown here typeid type name For example the following statement is perfectly acceptable cout lt lt typeid int name The main use of this form of typeid is to obtain a type_info object that describes the specified type so that it can be used in a type comparison statement Progress Check 1 What makes a static membe
39. In this example a and b are not declared until just before they are needed Frankly most programmers declare local variables at the beginning of the function that uses them but this is a stylistic issue Name Hiding When a local variable declared in an inner block has the same name as a variable declared in an outer block the variable declared in the inner block hides the one in the outer block For example include lt iostream gt using namespace std int main int i int j i 10 4 100 1f j gt 0 int i this i is separate from outer i i 2 cout lt lt inner i lt lt i lt lt n cout lt lt outer i lt lt i lt lt n return OQ The output from this program is shown here 15 This i hides the outer i C A Beginner s Guide by Herbert Schildt inner i 50 outer i 10 The i declared within the if block hides the outer i Changes that take place on the inner i have no effect on the outer i Furthermore outside of the if block the inner i is unknown and the outer i comes back into view Function Parameters The parameters to a function are within the scope of the function Thus they are local to the function Except for receiving the values of the arguments parameters behave like any other local variables Ask the Expert Q What does the keyword auto do have heard that it is used to declare local variables Is this right A The C languag
40. In this project you will create the Truck class In the process the instance variables in Vehicle will be made private and accessor functions are provided to get their values Step by Step 1 Create a file called TruckDemo cpp and copy the last implementation of Vehicle from Module 8 into the file 2 Create the Truck class as shown here Use Vehicle to create a Truck specialization class Truck public Vehicle int cargocap cargo capacity in pounds public This is a constructor for Truck Truck int p int f int m int c Vehicle p f m Cargocap c Accessor function for cargocap int get_cargocap return cargocap 19 C A Beginner s Guide by Herbert Schildt Here Truck inherits Vehicle adding the cargocap member Thus Truck includes all of the general vehicle attributes defined by Vehicle It need add only those items that are unique to its own class 3 Here is an entire program that demonstrates the Truck class Create a subclass of Vehicle called Truck include lt iostream gt using namespace std Declare the Vehicle class class Vehicle f These are private int passengers number of passengers int fuelcap fuel capacity in gallons int mpg fuel consumption in miles per gallon public This is a constructor for Vehicle Vehicle int p int int m passengers p fuelcap f mpg m Compute and return the range int range return mpg
41. Perhaps no other construct is as fundamental to programming as the variable A variable is a named memory location that can be assigned a value Further the value of a variable can be changed during the execution of a program That is the content of a variable is changeable not fixed The following program creates a variable called length gives it the value 7 and then displays the message The length is 7 on the screen 15 C A Beginner s Guide by Herbert Schildt Using a variable inelude lt iostream gt using namespace sted int maint int length this declares a variable Declare a variable length 7 this assigns 7 to length Asign length a value cout lt lt The length is cout lt lt length This displays 7 Output the value in length return OU As mentioned earlier the names of C programs are arbitrary Thus when you enter this program select a filename to your liking For example you could give this program the name VarDemo cpp This program introduces two new concepts First the statement int length this declares a variable declares a variable called length of type integer In C all variables must be declared before they are used Further the type of values that the variable can hold must also be specified This is called the type of the variable In this case length may hold integer values These are whole number values whose
42. That is a try block within a function can throw any type of exception as long as the exception is caught within that function The restriction applies only when throwing an exception outside of the function Rethrowing an Exception You can rethrow an exception from within an exception handler by calling throw by itself with no exception This causes the current exception to be passed on to an outer try catch sequence The most likely reason for calling throw this way is to allow multiple handlers access to the exception For example perhaps one exception handler manages one aspect of an exception and a second handler copes with another aspect An exception can only be rethrown from within a catch block or from any function called from within that block When you rethrow an exception it will not be recaught by the same catch statement It will propagate to the next catch statement The following program illustrates rethrowing an exception It rethrows a char exception Example of rethrowing an exception include lt iostream gt using namespace std void Xhandler try throw hello throw a char 12 C A Beginner s Guide by Herbert Schildt eatch char catch a char cout lt lt Caught char inside Xhandler n throw rethrow char out of function Rethrow an exception int main cout lt lt start n try Mhandler catch char cout lt lt Caught char
43. The destruction of this temporary object may cause unexpected side effects in some situations For example if the object returned by the function has a destructor that releases a resource such as memory or a file handle that resource will be freed even though the object that is assigned the return value is still using it The solution to this type of problem involves the use of a copy constructor which is described next One last point It is possible for a function to return an object by reference but you need to be careful that the object being referenced does not go out of scope when the function is terminated Progress Check 1 Constructors cannot be overloaded True or false 12 C A Beginner s Guide by Herbert Schildt 2 When an object is passed by value to a function a copy is made Is this copy destroyed when the function returns 3 When an object is returned by a function a temporary object is created that contains the return value True or false CRITICAL SKILL 9 5 Creating and Using a Copy Constructor As earlier examples have shown when an object is passed to or returned from a function a copy of the object is made By default the copy is a bitwise clone of the original object This default behavior is often acceptable but in cases where it is not you can control precisely how a copy of an object is made by explicitly defining a copy constructor for the class A copy constructor is a special type of overloaded
44. The loop iterates until the null terminating str is indexed Since a null is zero false the loop stops Here is the same program rewritten to use pointer arithmetic Reverse case using array indexing include lt iostream gt include lt cctype gt using namespace std int main int i char str 80 This Is A Test cout lt lt Original string lt lt str lt lt n for i 0 str i i if isupper str i str i tolower str i else if islower str i str i toupper str i cout lt lt Inverted case string lt lt str return 0 In this version p is set to the start of str Then inside the while loop the letter at p is checked and changed and then p is incremented The loop stops when p points to the null terminator that ends str Because of the way some C compilers generate code these two programs may not be equivalent in performance Generally it takes more machine instructions to index an array than it does to perform arithmetic on a pointer Consequently in professionally written C code it is common to see the pointer version used more frequently However as a beginning C programmer feel free to use array indexing until you are comfortable with pointers 31 C A Beginner s Guide by Herbert Schildt Indexing a Pointer As you have just seen it is possible to access an array using pointer arithmetic What you might find surprising is that the rev
45. The second is area which returns the area of the triangle Expand the Help class so that it stores an integer ID number that identifies each user of the class Display the ID when a help object is destroyed Return the ID when the function getID is called 37 C A Beginner s Guide by Herbert Schildt Module 9 A Closer Look at Classes Table of Contents CRITICAL SKILL 9 1 Overload contructors CRITICAL SKILL 9 2 Assign objects CRITICAL SKILL 9 3 Pass objects to functions CRITICAL SKILL 9 4 Return objects from functions CRITICAL SKILL 9 5 Create copy contructors CRITICAL SKILL 9 6 Use friend functions CRITICAL SKILL 9 7 Know the structure and union CRITICAL SKILL 9 8 Understand this CRITICAL SKILL 9 9 Know operator overlaoding fundamentals CRITICAL SKILL 9 10 Overlaod operators using member functions CRITICAL SKILL 9 11 Overlad operators using nonmember functions This module continues the discussion of the class begun in Module 8 It examines a number of class related topics including overloading constructors passing objects to functions and returning objects It also describes a special type of constructor called the copy constructor which is used when a copy of an object is needed Next friend functions are described followed by structures and unions and the this keyword The module concludes with a discussion of operator overloading one of C s most exciting features 1 C A Beginn
46. Thus when a Gamma object is created the constructors are called in this order Alpha Beta Gamma 7 A protected member in a base class can be accessed by its own class and by derived classes It is private otherwise 8 When a virtual function is called through a base class pointer it is the type of the object being pointed to that determines which version of the function will be called 9 A pure virtual function is a function that has no body inside its base class Thus a pure virtual function must be overridden by derived classes An abstract class is a class that contains at least one pure virtual function 10 No an abstract class cannot be used to create an object 11 A pure virtual function represents a generic description that all implementations of that function must adhere to Thus in the phrase one interface multiple methods the pure virtual function represents the interface and the individual implementations represent the methods Module 11 The C I O System 1 The predefined streams are cin cout cerr and clog 2 Yes C defines both 8 bit and wide character streams 3 The general form for overloading an inserter is shown here 31 C A Beginner s Guide by Herbert Schildt 10 11 12 32 ostream amp operator lt lt ostream amp stream class_type obj class specific code goes here return stream return the stream ios scientific causes numeric output to be displayed i
47. Use ThreeD inserter to output coordinates return 0 This program displays the following output L 2 3 3 4 5 5 6 7 If you eliminate the code that is specific to the ThreeD class you are left with the skeleton for an inserter function as shown here ostream amp operator lt lt ostream amp stream class_type obj class specific code goes here return stream return the stream Of course it is permissible for obj to be passed by reference Within wide boundaries what an inserter function actually does is up to you However good programming practice dictates that your inserter should produce reasonable output Just make sure that you return stream Using Friend Functions to Overload Inserters 6 C A Beginner s Guide by Herbert Schildt In the preceding program the overloaded inserter function is not a member of ThreeD In fact neither inserter nor extractor functions can be members of a class The reason is that when an operator function is amember of a class the left operand implicitly passed using the this pointer is an object of that class There is no way to change this However when inserters are overloaded the left operand is a stream and the right operand is an object of the class being output Therefore overloaded inserters must be nonmember functions The fact that inserters must not be members of the class they are defined to operate on raises a serious question How can an overload
48. a b aj lt b a Bb int main int x Y x 10 y 20 cout lt lt The minimum is lt lt MIN x y return 0 When this program is compiled the expression defined by MIN a b will be substituted except that x and y will be used as the operands That is the cout statement will be substituted to look like this cout lt lt The minimum is lt lt x lt y x y In essence the function like macro is a way to define a function that has its code expanded inline rather than called The apparently redundant parentheses surrounding the MIN macro are necessary to ensure proper evaluation of the substituted expression because of the relative precedence of the operators In fact the extra parentheses should be applied in virtually all function like macros Otherwise there can be surprising results For example consider this short program which uses a macro to determine whether a value is even or odd This program will give the wrong answer include lt iostream gt using namespace std define EVEN a at2 0 7 1 OQ int main if EVEN 94 1 cout lt lt is even else cout lt lt is odd return 0 This program will not work correctly because of the way the macro substitution is made When compiled the EVEN 9 1 is expanded to 3 C A Beginner s Guide by Herbert Schildt 9 1 2 0 1 0 As you should recall the modulus operator has higher precedence than
49. and C was created by Microsoft Because there is sometimes confusion about how these two languages relate to C a brief discussion of their relationship is in order C is the parent for both Java and C Although both Java and C added removed and modified various features in total the syntax for these three languages is nearly identical Furthermore the object model used by C is similar to the ones used by Java and C Finally the overall look and feel of these languages is very similar This means that once you know C you can easily learn Java or CH The opposite is also true If you know Java or C learning C is easy This is one reason that Java and C share C s syntax and object model it facilitated their rapid adoption by legions of experienced C programmers The main difference between C Java and C is the type of computing environment for which each is designed C was created to produce high performance programs for a specific type of CPU and operating system For example if you want to write a program that runs on an Intel Pentium under the Windows operating system then C is the best language to use Ask the Expert Q How do Java and C create cross platform portable programs and why can t C do the same A Java and C can create cross platform portable programs and C can t because of the type of object code produced by the compiler In the case of C the output from the compiler is
50. carriage return linefeed sequence is generated using the newline character To put a newline character into a string use this code n a backslash followed by a lowercase n To see the effect of the n try the following program Ts This program demonstrates the n code which generates a new line a include lt iostream gt using namespace std int main cout lt lt one n 6ouc lt lt iwon cout lt lt three Cout lt lt Four return This program produces the following output one Cwo threefour The newline character can be placed anywhere in the string not just at the end You might want to try experimenting with the newline character now just to make sure you understand exactly what it does 71 C A Beginner s Guide by Herbert Schildt Progress Check 1 What is C s input operator 2 To what device is cin linked by default 3 What does n stand for Answer Key 1 The input operator is gt gt 2 cinis linked to the keyboard by default 3 The n stands for the newline character Another Data Type In the preceding programs variables of type int were used However a variable of type int can hold only whole numbers Thus it cannot be used when a fractional component is required For example an int variable can hold the value 18 but not the value 18 3 Fortunately int is only one of several data types defined by C To allow numbers with fractional compo
51. done This sequence cannot be recoded into a switch because all three conditions involve different variables and differing types What variable would control the switch Also you will need to use an if else if ladder when testing floating point values or other objects that are not of types valid for use in a switch expression Start Building a C Help System This project builds a simple help system that displays the syntax for the C control Help cpp statements The program displays a menu containing the control statements and then waits for you to choose one After one is chosen the syntax of the statement is displayed In this first version of the program help is available for only the if and switch statements The other control statements are added by subsequent projects Step by Step 1 Create a file called Help cpp 2 The program begins by displaying the following menu Help on Le Lr 2 switch Choose one To accomplish this you will use the statement sequence shown here 11 C A Beginner s Guide by Herbert Schildt cout lt lt Help on n gt cout lt lt 1 arin cout lt lt T 2 switen in cout lt lt Choose one 3 Next the program obtains the user s selection as shown here cin gt gt choices 4 Once the selection has been obtained the program uses this switch statement to display the syntax for the selected statement switch choice case l cout
52. for i 0O i lt 10 i cout lt lt nums i lt lt cout lt lt n cube nums 10 compute cubes lt Pass address of nums to cubel cout lt lt Altered contents for i 0 i lt 10 i cout lt lt nums i lt lt return 0 Here is the output produced by this program 22 C A Beginner s Guide by Herbert Schildt Original contents 12345678910 Altered contents 1 8 27 64 125 216 343 512 729 1000 As you can see after the call to cube the contents of array nums in main will be cubes of its original values That is the values of the elements of nums have been modified by the statements within cube because n points to nums Passing Strings Because a string is simply a character array that is null terminated when you pass a string to a function only a pointer to the beginning of the string is actually passed This is a pointer of type char For example consider the following program It defines the function strinvertCase which inverts the case of the letters within a string Pass a string to a function tinclude lt iostream gt include lt cstring gt include lt cctype gt using namespace std void striInvertCase char str int main char str s0 strcpy str This Is A Test strinvertCase str cout lt lt str display modified string 23 C A Beginner s Guide by Herbert Schildt return O Invert the case of the letters within
53. fuelcap Accessor functions int get_passengers return passengers int get_fuelcap return fuelcap int get_mpg return mpg Use Vehicle to create a Truck specializatiol class Truck public Vehicle int cargocap cargo capacity in pounds public This is a constructor for Truck Truck int p int f int m int c Vehicle p E m cargocap c Accessor function for cargocap int get_cargocap return cargocap 20 C A Beginner s Guide by Herbert Schildt int main construct some trucks Truck semi 2 200 7 44000 Truck pickup 3 28 15 2000 int dist 252 cout lt lt Semi can carry lt lt seml get_cargocap lt lt pounds n cout lt lt It has a range of lt lt semi range lt lt miles n cout lt lt To go lt lt dist lt lt miles semi needs lt lt dist semi get_mpg lt lt gallons of fuel n n cout lt lt Pickup can carry lt lt pickup get_cargocap lt lt pounds n cout lt lt It has a range of lt lt pickup range lt lt miles n cout lt lt To go lt lt dist lt lt miles pickup needs lt lt dist pickup get_mpg lt lt gallons of fuel n return Q 4 The output from this program is shown here Semi can carry 44000 pounds It has a range of 1400 miles To go 252 miles semi needs 36 gallons of fuel Pickup can carry 2000 pounds It has a r
54. lt n i 10 Error i is private to B and access is not _ Can t access i because it is private to B int main D ob 3 ob set 1 2 access member of base class ob show access member of base class ob showk uses member of derived class return OQ Since set and show are public in B they can be called on an object of type D from within main Because i and j are specified as private they remain private to B This is why the line i 10 Error iis private to B and access is not allowed is Commented out D cannot access a private member of B The opposite of public inheritance is private inheritance When the base class is inherited as private then all public members of the base class become private members of the derived class For example g C A Beginner s Guide by Herbert Schildt the program shown next will not compile because both set and show are now private members of D and thus cannot be called from main Use private inheritance This program won t compile include lt iostream gt using namespace std class E int i j public void set int a int b i a j j b void show cout lt lt i lt lt lt lt j lt lt n by Public elements of B become private in D class D private B _ int k n Now inherit B as private public D int x k x void showk cout lt lt k lt lt
55. lt lt Teet as lt lt tm lt lt merers 7 6 Conclude the program as shown here return O 7 Your finished program should look like this Project L 1 This program converts feet to meters Call this program FLOM cpp aay include lt iostream gt using namespace std int main double f holds the length in feet double m holds the conversion to meters COUL lt lt Enter the length in Peers 7 cin gt gt fy read the number of feet m f 3 28 convert to meters GOUL lt T lt lt T feet 19 T lt lt m lt lt T merero 25 C A Beginner s Guide by Herbert Schildt return 0 8 Compile and run the program Here is a sample run Enter the length in feet 5 5 feet is 1 52439 meters 9 Try entering other values Also try changing the program so that it converts meters to feet Progress Check 1 What is C s keyword for the integer data type 2 What is double 3 How do you output a newline Answer Key 1 The integer data type is int 2 double is the keyword for the double floating point data type 3 To output a newline use n CRITICAL SKILL 1 8 Two Control Statements Inside a function execution proceeds from one statement to the next top to bottom It is possible however to alter this flow through the use of the various program control statements supported by C Although we will look closely at control statements later two are brie
56. lt lt Sorted order lt lt str lt lt n return 0 Set up a call to the actual sorting function void quicksort char items int len qs items 0 len 1 A recursive version of Quicksort for sorting characters void gqs char items int left int right int i j char x Y i left j right x items left right 2 do while items i lt x amp amp i lt right i while x lt items j amp amp j gt left j if i lt j y items i items i items j items j y Ltt J while i lt j 1f left lt j gqs items left j 1f i lt right gqs items i right The output from the program is shown here Original order jfmckldoelazlkper Sorted order acdeefjkklllmoprz Ask the Expert Q have heard of something called the default to int rule What is it and does it apply to C 38 C A Beginner s Guide by Herbert Schildt A In the original C language and for early versions of C if no type specifier was present ina declaration int was assumed For example in old style code the following function would be valid and would return an int result f default to int return type int x return x I Here the type returned by f is int by default since no other return type is specified However the default to int rule also called the implicit int rule is not supported by modern versions of C
57. n Notice that no default statement is present in this version of the switch Since the menu loop ensures that a valid response will be entered it is no longer necessary to include a default statement to handle an invalid choice 4 Here is the entire Help2 cpp program listing Project 3 2 An improved Help system that uses a a do while to process a menu selection i include lt iostream gt using namespace std int main char choice do cout cout Cout cout cout 25 lt lt lt lt lt Help on n 1 if n 2 switch n 3 for n 4 while n C A Beginner s Guide by Herbert Schildt cout lt lt Choose one cin gt gt choice while cout lt lt choice lt 1 choice gt 5 n Y n n n switch choice case 1 cout lt lt The if n n cout lt lt 1f condition statement n cout lt lt else statement n break case 2 cout lt lt The switch n n cout lt lt switch expression n cout lt lt case constant n cout lt lt statement sequencen cout lt lt break n cout lt lt rL cout lt lt n break case S3 cout lt lt The for n n cout lt lt for init condition increment cout lt lt statement n break case d cout lt lt The while n n cout lt lt while condition statement n break case S5 cout lt lt
58. parameter j receives p it then also points to i within main Thus the assignment j 100 causes i to be given the value 100 For the general case f assigns 100 to whatever address it is called with In the preceding example it is not actually necessary to use the pointer variable p Instead you can simply precede i with an amp when f is called This causes the address of i to be passed to f The revised program is shown here 19 C A Beginner s Guide by Herbert Schildt Pass a pointer to a function include lt iostream gt using namespace std void f int j int main int i f amp i 4 No need for p The address of i is passed directly cout lt lt i return 0 void f int j j 100 var pointed to by j is assigned 100 It is crucial that you understand one thing about passing pointers to functions when you perform an operation within the function that uses the pointer you are operating on the variable that is pointed to by that pointer Thus the function will be able to change the value of the object pointed to by the parameter Passing an Array When an array is an argument to a function the address of the first element of the array is passed not a copy of the entire array Recall that an array name without any index is a pointer to the first element in the array This means that the parameter declaration must be of a compatible type There are thre
59. parentheses that follow the function s name This same basic approach applies to all functions that use parameters To call box you must specify three arguments For example box 7 20 4 box 50 3 2 box 8 6 9 The values specified between the parentheses are arguments passed to box and the value of each argument is copied into its matching parameter Therefore in the first call to box 7 is copied into length 20 is copied into width and 4 is copied into height In the second call 50 is copied into length 3 into width and 2 into height In the third call 8 is copied into length 6 into width and 9 into height The following program demonstrates box A simple program that demonstrates box tinclude lt iostream gt using namespace std void box int length int width int height box s prototype int main box 7 20 4 lt Pass arguments to box box 50 3 2 box 6 9 return 0 These parameters receive he values of the arguments passed to box Compute the volume of a box void box int length int width int height cout lt lt volume of box is lt lt length width height lt lt n The output from the program is shown here volume of box is 560 volume of box is 300 volume of box is 432 Remember the term argument refers to the value that is used to call a function The variable that receives the value of an argument is called
60. program True or false 3 In a multifile project what specifier do you use to tell one file about a global variable declared in another file 4 What is the most important attribute of a static local variable 5 Write a program that contains a function called counter which simply counts how many times it is called Have it return the current count 6 Given this fragment which variable would most benefit from being specified as register 35 C A Beginner s Guide by Herbert Schildt int myfunc int x int y int z z 10 y 0 for x Zz x lt 15 X Y t Xj return y 7 How does amp differ from amp amp 8 What does this statement do lt 10 9 Using the rrotate and lrotate functions from Project 7 1 it is possible to encode and decode a string To code the string left rotate each letter by some amount that is specified by a key To decode right rotate each character by the same amount Use a key that consists of a string of characters There are many ways to compute the number of rotations from the key Be creative The solution shown in the online answers is only one of many 10 On your own expand show_ binary so that it shows all bits within an unsigned int rather than just the first eight 36 C A Beginner s Guide by Herbert Schildt Module amp Classes and Objects Table of Contents CRITICAL SKILL 8 1 The General Form of a Class CRITICAL SKILL 8 2
61. r gg min X a gg n cout lt lt min 9 3 lt lt min 9 3 lt lt n cout lt lt min amp 1il amp J lt lt min amp il amp 1 lt lt n return 0 min for ints Return the smallest value int min int a int b Each version of min can be f specialized This version if a lt b return a returns the smallest int value else return b 16 C A Beginner s Guide by Herbert Schildt min for chars ignore case char min char a char b lt This version of min ignores case 1f tolower a lt tolower b return a else return b min for int pointers Compare values and return pointer to smallest value a int min int a int b This version of min returns a pointer to if a lt b return a the smallest value else return bp Here 1s the output produced by the program min X a a min 9 3 3 min amp 1l amp J 10 When you overload a function each version of that function can perform any activity you desire That is there is no rule stating that overloaded functions must relate to one another However from a stylistic point of view function overloading implies a relationship Thus while you can use the same name to overload unrelated functions you should not For example you could use the name sar to create functions that return the square of an int and the square root of a double These t
62. return 1 answer factr n 1 n Execute a recursive call to factr return answer Iterative version int fact int n int t answer answer 1 for t 1 t lt n t answer answer t return answer The operation of the nonrecursive version of fact should be clear It uses a loop starting at 1 and progressively multiplies each number by the moving product The operation of the recursive factr is a little more complex When factr is called with an argument of 1 the function returns 1 otherwise it returns the product of factr n 1 n To evaluate this expression factr is called with n 1 This happens until n equals 1 and the calls to the function begin returning For example when the factorial of 2 is calculated the first call to factr will cause a second call to be made with the argument of 1 This call will return 1 which is then multiplied by 2 the original n value The answer is then 2 You might find it interesting to insert cout statements into factr that will show at what level each call is and what the intermediate answers are 33 C A Beginner s Guide by Herbert Schildt When a function calls itself new local variables and parameters are allocated storage usually on the system stack and the function code is executed with these new variables from the start As each recursive call returns the old local variables and parameters are removed from
63. return i Error i will go out of scope when f returns In f the local variable i will go out of scope when the function returns Therefore the reference to i returned by f will be undefined Actually some compilers will not compile f as written for precisely this reason However this type of problem can be created indirectly so be careful which object you return a reference to CRITICAL SKILL 6 6 Independent References Even though the reference is included in C primarily for supporting call by reference parameter passing and for use as a function return type it is possible to declare a stand alone reference variable This is called an independent reference It must be stated at the outset however that non parameter reference variables are seldom used because they tend to confuse and destructure your program With these reservations in mind we will take a short look at them here An independent reference must point to some object Thus an independent reference must be initialized when it is declared Generally this means that it will be assigned the address of a previously declared variable Once this is done the name of the reference variable can be used anywhere that the variable it refers to can be used In fact there is virtually no distinction between the two For example consider the program shown here Use an independent reference include lt iostream gt using namespace std int main
64. such as operating system command processors that require an infinite loop most infinite loops are really just loops with special termination requirements Near the end of this module you will see how to halt a loop of this type Hint It s done using the break statement Loops with No Body In C the body associated with a for loop can be empty This is because the null statement is syntactically valid Bodiless loops are often useful For example the following program uses one to sum the numbers from 1 to 10 The body of a for loop can be empty include lt iostream gt include lt cstdlib gt using namespace std 17 C A Beginner s Guide by Herbert Schildt int main int i int sum 0 f sum the numbers from 1 through 10 for i 1 i lt 10 sum i 4 This loop has no body cout lt lt Sum is lt lt sum return 0 The output from the program is shown here Sum is 55 Notice that the summation process is handled entirely within the for statement and no body is needed Pay special attention to the increment expression sum i Don t be intimidated by statements like this They are common in professionally written C programs and are easy to understand if you break them down into their parts In words this statement says add to sum the value of sum plus i then increment i Thus it is the same as this sequence of statements sum sum i i Declaring
65. that data will be received in string form Your program will need to convert it into the binary internal format using one of the standard library functions supported by C Three of the most commonly used functions for this purpose are shown here atof Converts a string to a double and returns the result atol Converts a string to a long int and returns the result atoil Converts a string fo an int and returns the result Each is called with a string containing a numeric value as an argument Each uses the header lt cstdlib gt The following program demonstrates the conversion of a numeric command line argument into its binary equivalent It computes the sum of the two numbers that follow its name on the command line The program uses the atof function to convert its numeric argument into its internal representation 28 C A Beginner s Guide by Herbert Schildt This program displays the sum of the two numeric command line arguments j include lt iostream gt include lt cstdlib gt using namespace std int main int argc char argv double a b if arge 3 cout lt lt Usage add num num n return 1 Use atof to convert command line numeric strings into doubles a atof argv 1 convert first command line arg b atof argv 2 convert second comnand line arg cout lt lt a b return OQ To add two numbers use this type of command line assuming the pro
66. time its block is entered j include lt iostream gt using namespace std void int main for int i 0 i lt 3 i return 0 num is initialized each time f is called void int num 99 lt pum is set to 99 each time f is called cout lt lt num lt lt n num this has no lasting effect The output shown here confirms that num is initialized each time f is called 3999 99 A local variable that is not initialized will have an unknown value until it is assigned one Local Variables Can Be Declared Within Any Block It is common practice to declare all variables needed within a function at the beginning of that function s code block This is done mainly so that anyone reading the code can easily determine what variables are used However the beginning of the function s block is not the only place where local variables can be declared A local variable can be declared anywhere within any block of code A variable declared within a block is local to that block This means that the variable does not exist until the block is entered and is destroyed when the block is exited Furthermore no code outside that block including other code in the function can access that variable To understand this try the following program 13 C A Beginner s Guide by Herbert Schildt Variables can be local to a block include lt iostream gt using namespace st
67. using namespace std ostream amp setup ostream amp stream A custom output manipulator stream setf ios left stream lt lt setw 10 lt lt setfill s return stream int main cout lt lt 10 lt lt lt lt setup lt lt 10 return Custom manipulators are useful for two reasons First you might need to perform an I O operation ona device for which none of the predefined manipulators applies a plotter for example In this case creating your own manipulators will make it more convenient when outputting to the device Second you may find that you are repeating the same sequence of operations many times You can consolidate these operations into a single manipulator as the foregoing program illustrates All parameterless input manipulator functions have this skeleton istream amp manip_name istream amp stream your code here return stream For example the following program creates the prompt manipulator It displays a prompting message and then configures input to accept hexadecimal 19 C A Beginner s Guide by Herbert Schildt Create an input manipulator include lt iostream gt include lt iomanip gt using namespace std istream amp prompt istream amp stream lt A custom input manipulator cin gt gt hex cout lt lt Enter number using hex format return stream int main int i cin gt gt prompt
68. y 100 O y 100 When creating a function that has default argument values the default values must be specified only once and this must happen the first time the function is declared within the file In the preceding example the default argument was specified in myfunc s prototype If you try to specify new or even the same default values in myfunc s definition the compiler will display an error message and will not compile your program Even though default arguments cannot be redefined within a program you can specify different default arguments for each version of an overloaded function that is different versions of the overloaded function can have different default arguments It is important to understand that all parameters that take default values must appear to the right of those that do not For example the following prototype is invalid Wrong void f int a 1 int b Once you ve begun defining parameters that take default values you cannot specify a nondefaulting parameter That is a declaration like the following is also wrong and will not compile int myfunc float f char str int i 10 int j Wrong Since i has been given a default value j must be given one too One reason that default arguments are included in C is that they enable the programmer to manage greater complexity To handle the widest variety of situations quite frequently a function will contain more parameters than are require
69. 0Q The output is shown here 0 0 10 10 In the program notice that the static integer num is both declared inside the ShareVar class and defined as a global variable As stated earlier this is necessary because the declaration of num inside ShareVar does not allocate storage for the variable C initializes num to O since no other initialization is given This is why the first calls to shownum both display 0 Next object a sets num to 10 Then both a and b use shownum to display its value Because there is only one copy of num shared by a and b both calls to shownum display 10 When a static variable is public it can be referred to directly through its class name without reference to any specific object It can also be referred to through an object For example Refer to static variable through its class name include lt iostream gt using namespace std class Test public static int num void shownum cout lt lt num lt lt endl 3 int Test num define num int main Test a Bb Set num through its class name Test num 100 lt Refer to num through its class name Test a shownum prints 100 b shownum prints 100 Set num through an object 43 C A Beginner s Guide by Herbert Schildt a num 200 4 a shownum prints 200 Refer to num through an object b shownum prints 200 return 0 Notice how the value
70. 1 2 3 Original value of b 10 10 10 Value of c after c a b 11 12 13 Value of c after c a b c 22 24 26 Value of c after c b a 1 2 3 Value of b after c b a 1 2 3 As you can see by looking at operator now both operands are passed to it The left operand is passed in op1 and the right operand in op2 39 C A Beginner s Guide by Herbert Schildt In many cases there is no benefit to using a friend function instead of a member function when overloading an operator However there is one situation in which a friend function is quite useful when you want an object of a built in type to occur on the left side of a binary operation To understand why consider the following As you know a pointer to the object that invokes a member operator function is passed in this In the case of a binary operator it is the object on the left that invokes the function This is fine provided that the object on the left defines the specified operation For example assuming some object called T which has assignment and integer addition defined for it then this is a perfectly valid statement T T 10 will work Since the object T is on the left side of the operator it invokes its overloaded operator function which presumably is capable of adding an integer value to some element of T However this statement won t work T 10 T won t work The problem with this statement is that the object on the le
71. 2 1s 0 1 5 2 is 1 Increment and Decrement Introduced in Module 1 the and the are the increment and decrement operators They have some special properties that make them quite interesting Let s begin by reviewing precisely what the increment and decrement operators do The increment operator adds 1 to its operand and the decrement operator subtracts 1 Therefore xX x 1 is the same as X 18 C A Beginner s Guide by Herbert Schildt is the same as Both the increment and decrement operators can either precede prefix or follow postfix the operand For example xXx x li can be written as x prefix form Or aS xt postfix form In this example there is no difference whether the increment is applied as a prefix or a postfix However when an increment or decrement is used as part of a larger expression there is an important difference When an increment or decrement operator precedes its operand C will perform the operation prior to obtaining the operand s value for use by the rest of the expression If the operator follows its operand then C will obtain the operand s value before incrementing or decrementing it Consider the following x 10 y x In this case y will be set to 11 However if the code is written as x LO 7 Rir then y will be set to 10 In both cases x is still set to 11 the difference is when it happens There are significant advantages in being a
72. D1_obj p 2whe access Dl s who Call the virtual function through a base class pointer p amp D2_ obj p gt who access D2 s who return 0 This program produces the following output Base First derivation Second derivation Let s examine the program in detail to understand how it works As you can see in B the function who is declared as virtual This means that the function can be redefined by a derived class Inside both D1 and D2 who is redefined relative to each class Inside main four variables are declared base_obj which is an object of type B p which is a pointer to B 30 C A Beginner s Guide by Herbert Schildt objects and D1_obj and D2_ obj which are objects of the two derived classes Next p is assigned the address of base_obj and the who function is called Since who is declared as virtual C determines at runtime which version of who to execute based on the type of object pointed to by p In this case p points to an object of type B so it is the version of who declared in B that is executed Next p is assigned the address of D1_obj Recall that a base class pointer can refer to an object of any derived class Now when who is called C again checks to see what type of object is pointed to by p and based on that type determines which version of who to call Since p points to an object of type D1 that version of who is used Likewise when p is assigned the ad
73. Defining a Class and Creating Objects CRITICAL SKILL 8 3 Adding Member Functions to a Class Project 8 1 Creating a Help Class CRITICAL SKILL 8 4 Constructors and Destructors CRITICAL SKILL 8 5 Parameterized Constructors CRITICAL SKILL 8 6 Inline Functions CRITICAL SKILL 8 7 Arrays of Objects CRITICAL SKILL 8 8 Initializing Object Arrays CRITICAL SKILL 8 9 Pointers to Objects Up to this point you have been writing programs that did not use any of C s object oriented capabilities Thus the programs in the preceding modules reflected structured programming not object oriented programming To write object oriented programs you will need to use classes The class is C s basic unit of encapsulation Classes are used to create objects Classes and objects are so fundamental to C that much of the remainder of this book is devoted to them in one way or another Class Fundamentals Let s begin by reviewing the terms class and object A class is a template that defines the form of an object A class specifies both code and data C uses a class specification to construct objects Objects are instances of aclass Thus a class is essentially a set of plans that specify how to build an object It is important to be clear on one issue a class is a logical abstraction It is not until an object of that class has been created that a physical representation of that class exists in memory When you define a class you declare the data
74. Herbert Schildt return OQ Here is a sample run The precise values you see may differ from these 0012FE5C 09012FE84 0012FE60 0012FE8C 0012FE64 0012FE94 0012FE68 0012FE9C 0012FE6C 0012FEA4 0012FE 0 O0012FEAC 0012FE7 74 0012FEB4 0012FE78 O0012FEBC 0012FE 7C 0012FEC4 0012FE80 0012FECC Pointer Comparisons Pointers may be compared using the relational operators such as lt and gt In general for the outcome of a pointer comparison to be meaningful the two pointers must have some relationship to each other For example both may point to elements within the same array You will see an example of this in Project 4 2 There is however one other type of pointer comparison any pointer can be compared to the null pointer which is zero Progress Check 1 All pointer arithmetic is performed relative to the of the pointer 2 Assuming that type double is 8 bytes long when a double pointer is incremented by how much is its value increased 3 In general two pointers can be meaningfully compared in what case CRITICAL SKILL 4 11 Pointers and Arrays In C there is a close relationship between pointers and arrays In fact frequently a pointer and an array are interchangeable Consider this fragment char str 80 char p1 pi str Here str is an array of 80 characters and p1 is a character pointer However it is the third line that is of interest In this line p1 is assigned the address of the first ele
75. It works like this the value of an expression is successively tested against a list of constants When a match is found the statement sequence associated with that match is executed The general form of the switch statement S switch expression case constant d statement sequence break case constant 2 statement sequence break case constants statement sequence break default statement Sequence j The switch expression must evaluate to either a character or an integer value Floatingpoint expressions for example are not allowed Frequently the expression controlling the switch is simply a variable The case constants must be integer or character literals The default statement sequence is performed if no matches are found The default is optional if it is not present no action takes place if all matches fail When a match is found the statements associated with that case are executed until the break is encountered or in a concluding case or default statement until the end of the switch is reached There are four important things to know about the switch statement The switch differs from the if in that switch can test only for equality that is for matches between the switch expression and the case constants whereas the if conditional expression can be of any type No two case constants in the same switch can have identical values Of course a switch statement enclosed by an outer switch may have case constant
76. The program generates a random number prompts for your guess and prints the message Right if you guess the magic number This program also introduces another C library function called rand which returns a randomly selected integer value It requires the lt cstdlib gt header Magic Number program include lt iostream gt include lt cstdlib gt using namespace std int main int magic magic number int guess user s guess magic rand get a random number cout lt lt Enter your guess cin gt gt guess if guess magic cout lt lt Right lt If the guess matches the magic number the return 0 message is displayed 2 C A Beginner s Guide by Herbert Schildt This program uses the if statement to determine whether the user s guess matches the magic number If it does the message is printed on the screen Taking the Magic Number program further the next version uses the else to print a message when the wrong number is picked Magic Number program lst improvement include lt iostream gt include lt cstdlib gt using namespace std int main int magic magic number int guess user s guess magic rand get a random number cout lt lt Enter your guess F cin gt gt guess if guess magic cout lt lt Right else cout lt lt Sorry you re wrong 4 Indicate
77. a constructor for TwoDShape that initializes the width and height properties 14 C A Beginner s Guide by Herbert Schildt if Add a constructor to TwoDShape include lt iostream gt include lt cstring gt using namespace std if A class for two dimensional objects class TwobShape these are private double width double height public f Constructor for TwobDsShape TwoDshape double w double hh f width w height h void showDim cout lt lt Width and height are lt lt width lt lt and lt lt height lt lt n accessor functions double getWidth return width double getHeight return height void setWidth double w width w void setHeight double h height h Triangle is derived from TwoDShape class Triangle public TwoDShape char style 20 now private public Constructor for Triangle Triangle char str double w double h TwoDShape w h Call the TwoDShape construct strepy style str double areal return getWidth getHeight 2 void showStyle 15 C A Beginner s Guide by Herbert Schildt cout lt lt Triangle is lt lt style lt lt n i int main Triangle tl isosceles 4 0 4 0 Triangle t2 right 8 0 12 0 cout lt lt Info for ti n tl showStyle tl showDim cout lt lt Area is lt lt tl area lt lt n
78. a built in type You can act on objects of that class through operators and use objects of that class in expressions To illustrate the creation and integration of a new class into the C environment this project creates a class called Set that defines a set type Before we begin it is important to understand precisely what we mean by a set For the purposes of this project a set is a collection of unique elements That is no two elements in any given set can be the same The ordering of a set s members is irrelevant Thus the set A B C 44 C A Beginner s Guide by Herbert Schildt is the same as the set A C B A set can also be empty Sets support a number of operations The ones that we will implement are e Adding an element to a set e Removing an element from a set e Set union e Set difference Adding an element to a set and removing an element from a set are self explanatory operations The other two warrant some explanation The union of two sets is a set that contains all of the elements from both sets Of course no duplicate elements are allowed We will use the operator to perform a set union The difference between two sets is a set that contains those elements in the first set that are not part of the second set We will use the operator to perform a set difference For example given two sets S1 and S2 this statement removes the elements of S2 from S1 putting the result in S3 S3 S1 S2 If S1
79. about the preceding example Because sqrt is part of the C standard function library it requires the standard header lt cmath gt which is included in the program The long double type lets you work with very large or small numbers It is most useful in scientific programs For example the long double type might be useful when analyzing astronomical data The bool Type The bool type is a relatively recent addition to C It stores Boolean that is true false values C defines two Boolean constants true and false which are the only two values that a bool value can have Before continuing it is important to understand how true and false are defined by C One of the fundamental concepts in C is that any nonzero value is interpreted as true and zero is false This g C A Beginner s Guide by Herbert Schildt concept is fully compatible with the bool data type because when used in a Boolean expression C automatically converts any nonzero value into true It automatically converts zero into false The reverse is also true when used in a non Boolean expression true is converted into 1 and false is converted into zero The convertibility of zero and nonzero values into their Boolean equivalents is especially important when using control statements as you will see in Module 3 Here is a program that demonstrates the bool type Demonstrate bool values include lt iostream gt using namespace std int mainii bool b
80. and binary A text stream is used with characters When a text stream is being used some character translations may take place For example when the newline character is output it may be converted into a carriage return linefeed sequence For this reason there might not be a one to one correspondence between what is sent to the stream and what is written to the file A binary stream can be used with any type of data No character translations will occur and there is a one to one correspondence between what is sent to the stream and what is actually contained in the file One more concept to understand is that of the current location The current location also referred to as the current position is the location in a file where the next file access will occur For example if a file is 100 bytes long and half the file has been read the next read operation will occur at byte 50 which is the current location 2 C A Beginner s Guide by Herbert Schildt To summarize In C I O is performed through a logical interface called a stream All streams have similar properties and every stream is operated upon by the same I O functions no matter what type of file it is associated with A file is the actual physical entity that contains The C I O System the data Even though files differ streams do not Of course some devices may not support all operations such as random access operations so their associated streams will not support the
81. another way to write the preceding declaration int sqrs 10 2 i1 1 2 4 3 9 4 16 6 25 6 36 7 49 8 64 9 81 10 100 When using subaggregate grouping if you don t supply enough initializers for a given group the remaining members will automatically be set to zero The following program uses the sars array to find the square of a number entered by the user It first looks up the number in the array and then prints the corresponding square include lt iostream gt using namespace std int main int i j int sqrs 10 2 il 1 12 4 13 9 4 16 5 25 6 36 7 49 8 64 19 C A Beginner s Guide by Herbert Schildt 9 81 10 100 cout lt lt Enter a number between 1 and 10 cin gt gt i look up i for j 0 j lt 10 j if sqrs j O i break cout lt lt The square of lt lt lt lt is cout lt lt sqrs j 1 return O Here is asample run Enter a number between 1 and 10 4 The square of 4 is 16 Unsized Array Initializations When declaring an initialized array it is possible to let C automatically determine the array s dimension To do this do not specify a size for the array Instead the compiler determines the size by counting the number of initializers and creating an array large enough to hold them For example int nums 1 2 3 4 creates an array called nums that
82. are creating a function that can automatically overload itself A generic function is created using the keyword template The normal meaning of the word template accurately reflects its use in C It is used to create a template or framework that describes what a function will do leaving it to the compiler to fill in the details as needed The general form of a generic function definition is shown here template lt class Ttype gt ret type func name parameter list body of function Here Ttype is a placeholder name for a data type This name is then used within the function definition to declare the type of data upon which the function operates The compiler will automatically replace Ttype with an actual data type when it creates a specific version of the function Although the use of the keyword class to specify a generic type in a template declaration is traditional you may also use the keyword typename 14 C A Beginner s Guide by Herbert Schildt The following example creates a generic function that swaps the values of the two variables with which it is called Because the process of exchanging two values is independent of the type of the variables it is a good candidate for being made into a generic function Function template example include lt iostream gt using namespace std A generic function that This is a function template exchanges the values of its template lt class X gt void swapargs X
83. are not very useful You may not know much about C at this point but you can still put what you have learned to work to create a practical program In this project we will create a program that converts feet to meters The program prompts the user for the number of feet It then displays that value converted into meters A meter is equal to approximately 3 28 feet Thus we need to use floating point data To perform the conversion the program declares two double variables One will hold the number of feet and the second will hold the conversion to meters Step by Step 1 Create a new C file called FtoM cpp Remember in C the name of the file is arbitrary so you can use another name if you like 2 Begin the program with these lines which explain what the program does include the iostream header and specify the std namespace Project i This program converts feet to meters Call this program FtoM cpp mip 24 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std 3 Begin main by declaring the variables f and m int main double f holds the length in feet double m holds the conversion to meters 4 Add the code that inputs the number of feet COU lt lt TEnter elie tengih in creer 3 Cin gt gt f read the number of feet 5 Add the code that performs the conversion and displays the result m 3 28 convert to meters Cour lt lt 2
84. are null terminated can often be used to simplify various operations For example the following program converts a string to uppercase 15 C A Beginner s Guide by Herbert Schildt Convert a string to uppercase include lt iostream gt include lt cestring gt include lt cctype gt using namespace std int main char str 80 int i strepy str this is a test for 1i 0 str i i str i toupper str i t This loop stops when the cout lt lt str null terminator is indexed return 0 The output from this program is shown here THIS IS A TEST This program uses the library function toupper which returns the uppercase equivalent of its character argument to convert each character in the string The toupper function uses the header lt cctype gt Notice that the test condition of the for loop is simply the array indexed by the control variable The reason this works is that a true value is any non zero value Remember all character values are non zero but the null terminating the string is zero Therefore the loop runs until it encounters the null terminator which causes str i to become zero Because the null terminator marks the end of the string the loop stops precisely where it is supposed to You will see many examples that use the null terminator in a similar fashion in professionally written C code Ask the Expert Q Besides toupper does C support other character manipul
85. at runtime what casting operator do you use What does const_cast do On your own try putting the Queue class from Project 12 1 in its own namespace called QueueCode and into its own file called Queue cpp Then rework the main function so that it uses a using statement to bring QueueCode into view Continue to learn about C It is the most powerful computer language currently available Mastering it puts you in an elite league of programmers 53 C A Beginner s Guide by Herbert Schildt Answers to Mastery Checks Module 1 C Fundamentals 1 C is at the center of modern programming because it was derived from C and is the parent of Java and C These are the four most important programming languages 2 True a C compiler produces code that can be directly executed by the computer 3 Encapsulation polymorphism and inheritance are the three guiding principles of OOP 4 C programs begin execution at main 5 A header contains information used by the program 6 lt iostream gt is the header the supports I O The statement includes the lt iostream gt header in a program 7 Anamespace is a declarative region in which various program elements can be placed Elements declared in one namespace are separate from elements declared in another 8 A variable isa named memory location The contents of a variable can be changed during the execution of a program 9 The invalid variables are d and e Variable names
86. can be accessed as quickly as possible Typically this means storing the variable either in a register of the CPU or in cache memory As you probably know accessing the registers of the CPU or cache memory is fundamentally faster than accessing the main memory of the computer Thus a variable stored in a register will be accessed much more quickly than if that variable had been stored in RAM Because the speed by which variables can be accessed has a profound effect on the overall soeed of your programs the careful use of register is an important programming technique Technically register is only a request to the compiler which the compiler is free to ignore The reason for this is easy to understand there are a finite number of registers or fast access memory and these may differ from environment to environment Thus if the compiler runs out of fast access memory it simply stores the variable normally Generally this causes no harm but of course the register advantage is lost You can usually count on at least two variables being optimized for speed Since only a limited number of variables can actually be granted the fastest access it is important to choose carefully those to which you apply the register modifier Only by choosing the right variables can you gain the greatest increase in performance In general the more often a variable is accessed the more benefit there will 10 C A Beginner s Guide by Herbert Schildt be to o
87. causes program flow to exit from the entire switch statement and resume at the next statement outside the switch However if a g C A Beginner s Guide by Herbert Schildt break statement does not end the statement sequence associated with a case then all the statements at and below the matching case will be executed until a break or the end of the switch is encountered For example study the following program carefully Can you figure out what it will display on the screen A switch without break statements include lt iostream gt using namespace std int mair int i for i 0 i lt 5 i Sswitch i case 0 cout lt lt less than 1 n case 1 cout lt lt less than 2 n case 2 cout lt lt less than 3 n No break statements he Case 3 cout lt lt less than 4 n case 4 cout lt lt less than 5 n cout lt lt n return 0 This program displays the following output less less less less less less less less less less less less less less less than than than than than than than than than than Chan Chan Chan Chan Chan 1 2 3 A 5 5 9 C A Beginner s Guide by Herbert Schildt As this program illustrates execution will continue into the next case if no break statement is present You can have empty cases as shown in this example Switch i case 1 case 3 Empty case sequences case 3 cout lt
88. char style 20 double area return getWidth getHeight 2 Use the accessor functions to 1 obtain the width and height void showStyle cout lt lt Triangle is lt lt style lt lt n int main f Triangle tl Triangle t2 tl setWidth 4 0 tl setHeight 4 0 strepy tl style isosceles t2 setWidth s8 0 t2 setHeight 12 0 strepy t2 style right 6 C A Beginner s Guide by Herbert Schildt cout lt lt Info for tl n tl showstyle ti showDim cout lt lt Area is lt lt tl area lt lt n cout lt lt n cout lt lt Info for t2 n t2 showstyle 2 showDim cout lt lt Area is lt lt t2 area lt lt n return 0 Progress Check 1 How isa base class inherited by a derived class 2 Does a derived class include the members of its base class 3 Does a derived class have access to the private members of its base class CRITICAL SKILL 10 2 Base Class Access Control As explained when one class inherits another the members of the base class become members of the derived class However the accessibility of the base class members inside the derived class is determined by the access specifier used when inheriting the base class The base class access specifier must be public private or protected If the access specifier is not used then it is private by default if the derived class is a class If the derived class is a
89. class called ColorTriangle ColorTriangle inherits all of the traits of Triangle and TwoDShape and adds a field called color which holds the color of the triangle A multilevel hierarchy include lt iostream gt include lt cstring gt using namespace std A class for two dimensional objects class TwoDShape these are private double width double height public Default constructor TwobShape f width height 0 0 Constructor for TwoDShape TwoDshape double w double h width w height h Construct object with equal width and height TwobShape double x width height x void showDim cout lt lt Width and height are width lt lt and lt lt height lt lt n lt lt 22 C A Beginner s Guide by Herbert Schildt accessor functions double getWidth return width double getHeight return height void setWidth double w width w void setHeight double h height h Triangle is derived from TwoDShape class Triangle public TwoDShape char style 20 now private public A default constructor This automatically invokes Che default constructor of TwoDShape Triangle strepy style unknown Constructor with three parameters Triangle char str double w double h TwoDShape w h f strcpy style str Construct an isosceles triangle Triangle double x TwoDShape x st
90. class specialization include lt iostream gt using namespace std template lt class T gt class MyClass T X public MyClass T a cout lt lt Inside generic MyClass n x a T getx return x F Explicit specialization for int template lt gt class MyClass lt int gt int x public This is an explicit specialization of MyClass MyClass int a cout lt lt Inside MyClass lt int gt specialization n x a ay int getx return x int main MyClass lt double gt d 10 1 cout lt lt double lt lt d getx lt lt n n MyClass lt int gt i 5 _ This uses the explicit specialization cout lt lt int lt lt i getx lt lt n of MyClass return 0 This program displays the following output 22 C A Beginner s Guide by Herbert Schildt Inside generic MyClass double 10 1 Inside MyClass lt int gt specialization iis 23 In the program pay close attention to this line template lt gt class MyClass lt int gt It tells the compiler that an explicit integer specialization of MyClass is being created This same general syntax is used for any type of class specialization Explicit class specialization expands the utility of generic classes because it lets you easily handle one or two special cases while allowing all others to be automatically processed by the compiler Of course if you find that you are
91. connected to many different types of CPUs and operating systems Thus the ability to produce cross platform portable programs became an overriding concern The first language to address this need was Java Using Java it is possible to write a program that runs in a wide variety of environments Thus a Java program can move about freely on the Internet However the price you pay for portability is efficiency and Java programs execute more slowly than do C programs The same is true for CH In the final analysis if you want to create high performance software use C If you need to create highly portable software use Java or CH One final point Remember that C Java and C are designed to solve different sets of problems It is not an issue of which language is best in and of itself Rather it is a question of which language is right for the job at hand Progress Check 1 From what language is C derived 2 What was the main factor that drove the creation of C 3 C isthe parent of Java and C True or False 6 C A Beginner s Guide by Herbert Schildt Answer Key 1 C is derived from C 2 Increasing program complexity was the main factor that drove the creation of C 3 True CRITICAL SKILL 1 3 Object Oriented Programming Central to C is object oriented programming OOP As just explained OOP was the impetus for the creation of C Because of this it is useful to understand OOP s basi
92. creation of the Standard Template Library STL by Alexander Stepanov The STL is a set of generic routines that you can use to manipulate data It is both powerful 4 C A Beginner s Guide by Herbert Schildt and elegant But it is also quite large Subsequent to the first draft the committee voted to include the STL in the specification for C The addition of the STL expanded the scope of C well beyond its original definition While important the inclusion of the STL among other things slowed the standardization of C It is fair to say that the standardization of C took far longer than anyone had expected In the process many new features were added to the language and many small changes were made In fact the version of C defined by the ANSI ISO C committee is much larger and more complex than Stroustrup s original design The final draft was passed out of committee on November 14 1997 and an ANSI ISO standard for C became a reality in 1998 This is the specification for C that is usually referred to as Standard C The material in this book describes Standard C This is the version of C supported by all mainstream C compilers including Microsoft s Visual C Thus the code and information in this book are fully portable CRITICAL SKILL 1 2 How C Relates to Java and C In addition to C there are two other important modern programming languages Java and C Java was developed by Sun Microsystems
93. declaration and precede it with the friend keyword For example in this fragment frnd is declared to be a friend of the class MyClass class MyClass public friend void frnd MyClass ob As you can see the keyword friend precedes the rest of the prototype A function can be a friend of more than one class Here is a short example that uses a friend function to determine if the private fields of MyClass have a common denominator 16 C A Beginner s Guide by Herbert Schildt Demonstrate a friend function include lt iostream gt using namespace std class MyClass int a b comDenom is a public friend of MyClass MyClass int i int j a 1 b j friend int comDenom MyClass x a friend function Notice that comDenom is a not a member function of any class int comDenom MyClass x Because comDenom is a friend of MyClass it can directly access a and b int max X a lt x b x a xX b for int i1 2 i lt max i 1f x a i 0 amp amp x b 1 0 return i return int main comDenom is called normally without the MyClass n 18 111 use of an object or the dot operator if comDenon r cout lt lt Common denominator is comDenom n lt lt lt wn else cout lt lt No common denominator n return OQ In this example the comDenom function is not a member of MyClass However it still has full a
94. derived try throw derived era a hir ele inne cout lt lt Caught a base class n wrong order You must catch derived classes ec 26h d Ce 4 before base classes cout lt lt This won t execute n return OQ Here because derived is an object that has B as a base class it will be caught by the first catch clause and the second clause will never execute Some compilers will flag this condition with a warning message Others may issue an error message and stop compilation Either way to fix this condition reverse the order of the catch clauses Catching All Exceptions In some circumstances you will want an exception handler to catch all exceptions instead of just a certain type To do this use this form of catch catch process all exceptions Here the ellipsis matches any type of data The following program illustrates catch 9 C A Beginner s Guide by Herbert Schildt This example catches all exceptions include lt iostream gt using namespace std void Xhandler int test try if test 0 throw test throw int if test 1 throw a throw char if test 2 throw 123 23 throw double catch catch all exceptions Catch all exceptions cout lt lt Caught One n int main cout lt lt start n handler 0 shandler 1 Mhandler 2 cout lt lt end return This program displays the follo
95. dimensional array is in essence a list of one dimensional arrays To declare a two dimensional integer array twoD of size 10 20 you would write int twoD 10 20 Pay careful attention to the declaration Unlike some other computer languages which use commas to separate the array dimensions C places each dimension in its own set of brackets Similarly to access an element specify the indices within their own set of brackets For example for point 3 5 of array twoD you would use twoD 3 5 In the next example a two dimensional array is loaded with the numbers 1 through 12 6 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std int main int t i nums 3 4 For t 0 t lt 3 t for i 0 i lt 4 i nums t i t 4 i 1 Indexing nums requires two indexes cout lt lt nums t 1 lt lt cout lt lt n return 0 In this example nums 0 0 will have the value 1 nums 0 1 the value 2 nums 0 2 the value 3 and so on The value of nums 2 3 will be 12 Conceptually the array will look like that shown here 0 1 2 3 Right index Left index nums 1 2 Two dimensional arrays are stored in a row column matrix where the first index indicates the row and the second indicates the column This means that when array elements are accessed in the order in which they are actually stored in memory the right i
96. division 33 davar aller division 32323338 Ask the Expert Q Why does C have different data types for integers and floating point values That is why aren t all numeric values just the same type 23 C A Beginner s Guide by Herbert Schildt A C supplies different data types so that you can write efficient programs For example integer arithmetic is faster than floating point calculations Thus if you don t need fractional values then you don t need to incur the overhead associated with types float or double Also the amount of memory required for one type of data might be less than that required for another By supplying different types C enables you to make the best use of system resources Finally some algorithms require or at least benefit from the use of a specific type of data C supplies a number of built in types to give you the greatest flexibility As you can see when ivar is divided by 3 a whole number division is performed and the outcome is 33 the fractional component is lost However when dvar is divided by 3 the fractional component is preserved There is one other new thing in the program Notice this line cout lt lt n print a blank line It outputs a newline Use this statement whenever you want to add a blank line to your output Project 1 1 Converting Feet to Meters Although the preceding sample programs illustrate several important features of the C language they
97. easier too The following example illustrates this application of const include lt iostream gt using namespace std const int num_employees 100 This creates a named constant called num_employees that has the value 100 int main int empNums num_employees num_employees is used here to double salary num_employees specify the size of the arrays char names num_employees i In this example if you need to use a new size for the arrays you need change only the declaration of num_employees and then recompile the program All three arrays will then automatically be resized Another important use of const is to prevent an object from being modified through a pointer For example you might want to prevent a function from changing the value of the object pointed to by a parameter To do this declare a pointer parameter as const This prevents the object pointed to by the parameter from being modified by a function That is when a pointer parameter is preceded by const 2 C A Beginner s Guide by Herbert Schildt no statement in the function can modify the variable pointed to by that parameter For example the negate function in the following program returns the negation of the value pointed to by its parameter The use of const in the parameter declaration prevents the code inside the function from modifying the value pointed to by the parameter Use a const pointer parameter
98. encapsulation principle of OOP 7 C A Beginner s Guide by Herbert Schildt Overloading Extractors To overload an extractor use the same general approach that you use when overloading an inserter For example the following extractor inputs 3 D coordinates into an object of type ThreeD Notice that it also prompts the user Get three dimensional values ThreeD extractor istream amp operator gt gt istream amp stream ThreeD amp obj cout lt lt Enter X Y 4 values stream gt gt obj x gt gt obj y gt gt obj z return stream An extractor must return a reference to an object of type istream Also the first parameter must be a reference to an object of type istream This is the stream that occurs on the left side of the gt gt The second parameter is a reference to the variable that will be receiving input Because it is a reference the second parameter can be modified when information is input The skeleton of an extractor is shown here istream amp operator gt gt istream amp stream object_type amp obj f put your extractor code here return stream The following program demonstrates the extractor for objects of type ThreeD g C A Beginner s Guide by Herbert Schildt Demonstrate a custom extractor include lt iostream gt using namespace std class ThreeD int x Y Z 3 D coordinates public ThreeD int a int b int c Xx a y b z C friend ostream S
99. example the loop control variable is called num Show square roots of 1 to 99 include lt iostream gt include lt cmath gt using namespace std int main int num double sq_root for num 1 num lt 100 num sq root sqrt double num cout lt lt num lt lt lt lt sq _ root lt lt n F return This program uses the standard function sqrt As explained in Module 2 the sart function returns the square root of its argument The argument must be of type double and the function returns a value of type double The header lt cmath gt is required The for loop can proceed in a positive or negative fashion and it can increment the loop control variable by any amount For example the following program prints the numbers 50 to 50 in decrements of 10 A negatively running for loop include lt iostream gt using namespace std int main int i for i 50 i gt 50 i 1 10 cout lt lt i lt lt 7 return 0 A negatively running for loop 14 C A Beginner s Guide by Herbert Schildt Here is the output from the program oO 20 30 20 LO 0 Sl 20 gt 30 40 30 An important point about for loops is that the conditional expression is always tested at the top of the loop This means that the code inside the loop may not be executed at all if the condition is false to begin with Here is an example TOL COUNnTH I10 count lt 57 count c
100. failures why doesn t C provide bounds checking on array operations A C was designed to allow professional programmers to create the fastest most efficient code possible Toward this end very little runtime error checking is included because it slows often dramatically the execution of a program Instead C expects you the programmer to be responsible enough to prevent array overruns in the first place and to add appropriate error checking on your own 5 C A Beginner s Guide by Herbert Schildt as needed Also it is possible for you to define array types of your own that perform bounds checking if your program actually requires this feature If an array overrun occurs during an assignment operation memory that is being used for other purposes such as holding other variables might be overwritten If an array overrun occurs when data is being read then invalid data will corrupt the program Either way as the programmer it is your job both to ensure that all arrays are large enough to hold what the program will put in them and to provide bounds checking whenever necessary Progress Check 1 What is a one dimensional array 2 The index of the first element in an array is always zero True or false 3 Does C provide bounds checking on arrays CRITICAL SKILL 4 2 Two Dimensional Arrays C allows multidimensional arrays The simplest form of the multidimensional array is the two dimensional array A two
101. false when the strings match Therefore you will need to use the operator if you want something to occur when the strings are equal For example the condition controlling the following if statement is true when str is equal to C if stremp str C cout lt lt str is C strlen The general form of a call to strlen is strlen s where s is a string The strlen function returns the length of the string pointed to by s 14 C A Beginner s Guide by Herbert Schildt A String Function Example The following program illustrates the use of all four string functions Demonstrate the string functions include lt iostream gt include lt cstdio gt include lt cstring gt using namespace std int main char eL e0 e230 Strepy si Ctr strepy s2 1S power programming cout lt lt lengths lt lt strilen sl GOUL lt lt a lt Strilen e2 lt lt in if strcemp sl s2 cout lt lt The strings are equal n else cout lt lt not equal n Stircar Sl SZ 3 GOUL lt sl lt Yin StrCpy Sz 21 SCout lt lt sl lt lt T and lt lt 52 lt lt TAn if strcemp sl s2 cout lt lt sl and s2 are now the same n return O Here is the output lengths 3 22 not equal C 1S power programming C 1S power programming and C 1S power programming sl and s2 are now the same Using the Null Terminator The fact that strings
102. goes about doing its work In other words you can use comments to provide a play by play description of what your program does In C there are two types of comments The one you ve just seen is called a multiline comment This type of comment begins with a a slash followed by an asterisk It ends only when a is encountered Anything between these two comment symbols is completely ignored by the compiler Multiline comments may be one or more lines long The second type of comment single line is found a little further on in the program and will be discussed shortly The next line of code looks like this include lt iostream gt 12 C A Beginner s Guide by Herbert Schildt The C language defines several headers which contain information that is either necessary or useful to your program This program requires the header iostream which supports the C I O system This header is provided with your compiler A header is included in your program using the include directive Later in this book you will learn more about headers and why they are important The next line in the program is using namespace std This tells the compiler to use the std namespace Namespaces are a relatively recent addition to C Although namespaces are discussed in detail later in this book here is a brief description A namespace creates a declarative region in which various program elements can be placed Elements declared in one namesp
103. gt amp return t Display the bits within a byte void show_binary unsigned int u i int t for t 128 t gt 0 t t 2 itfu amp t cout lt lt 1 else cout lt lt Q cout lt lt n Module 8 Classes and Objects 23 C A Beginner s Guide by Herbert Schildt A class is a logical construct that defines the form of an object An object is an instance of a class Thus an object has physical reality within memory To define a class use the class keyword Each object has its own copy of the member variables of a class class Test int count int max A constructor has the same name as its class A destructor has the same name as its class except that it is preceded by a Here are three ways to create an object that initializes i to 10 Sample ob 10 Sample ob 10 Sample ob Sample 10 When a member function is declared within a class it is automatically inlined if possible Create a Triangle class 24 C A Beginner s Guide by Herbert Schildt include lt iostream gt include lt cmath gt using namespace std class Triangle double height double base public Triangle double h double b height base b h double hypot return sqrt height height base base double area f return base height 2 0 F int main Triangle t1 3 0 4 0 Triangle t2 4 5 6 75 cout EL cout t1 cout t2 cout t
104. has nothing to do with inheritance or class hierarchies The name function returns a pointer to the name of the type Here is a Simple example that uses typeid 46 C A Beginner s Guide by Herbert Schildt A simple example that uses typeid include lt iostream gt include lt typeinfo gt using namespace std class MyClass fd int main ene a ae float f Use typeid to obtain the MyClass ob type of an object at runtime cout lt lt The type of i is lt lt typelid i name cout lt lt endl cout lt lt The type of f is lt lt typeid f name cout lt lt endl cout lt lt The type of ob is lt lt typeid ob name cout lt lt n n 1f typeid i typeid j cout lt lt The types of i and j are the same n 1f typeid i typeid f cout lt lt The types of i and f are not the same n return 0 The The The The The The output produced by this program is shown here type of i is int type of f is float type of ob is class MyClass types of i and j are the same types of i and f are not the same Perhaps the most important use of typeid occurs when it is applied through a pointer of a polymorphic base class that is a class that includes at least one virtual function In this case it will automatically return the type of the actual object being pointed to which may be a base class object or an object derived from that b
105. i 0 i lt 8 i ch lrotate ch 1 show_binary ch return OQ Lett rotate a byte n places unsigned char lrotate unsigned char val int n unsigned int t t val for int i 0 i lt n i t t lt lt 1 If a bit shifts out it will be in bit 8 of the integer t If this is the case put that bit on the right side 1f t amp 256 t t 1 put al on the right end return t return the lower 8 bits Right rotate a byte n places unsigned char rrotate unsigned char val int n unsigned int t t val First move the value 8 bits higher t t lt lt amp for int i 0O i lt n i t t gt gt 1 If a bit shifts out it will be in bit 7 of the integer t If this is the case put that bit on the left side 1f t amp 128 23 C A Beginner s Guide by Herbert Schildt t t 32768 put a 1 on left end Finally move the result back to the lower 8 bits of t t t gt gt amp return tC Display the bits within a byte void show_binary unsigned int u int t for t 128 t gt 0 t t 2 if u amp t cout lt lt 1 else cout lt lt 0 cout lt lt n 5 The output from the program is shown here Original value in binary 01010 100 Rotating right 8 times 00101010 0001010 1 1o00606d21L ChU6UOlhd1 CUO 0200010 1 10100010 01010001 10210310 0 0 01010100 Rotating left 8 times 1 10100
106. if they differ The following program illustrates this concept Friend functions can be shared by two or more classes include lt iostream gt using namespace std class Cylinder a forward declaration enum colors red green yellow class Cube colors color public Cube colors c color c friend bool sameColor Cube x Cylinder y 4 i class Cylinder colors color sameColor is a friend of Cube public Cylinder colors c color c friend bool sameColor Cube x Cylinder y sameColor is also i a friend of Cylinder F bool sameColor Cube x Cylinder y 1 x color y color return true else return false int main Cube cubel red Cube cubes green Cylinder cyl green Lf sameColor cubel cyl cout lt lt cubel and cyl are the same color n else cout lt lt cubel and cyl are different colors n 1f sameColor cube2 cyl cout lt lt cube and cyl are the same color n alse cout lt lt cube and cyl are different colors n return 0 18 C A Beginner s Guide by Herbert Schildt The output produced by this program is shown here cube1 and cyl are different colors cube2 and cyl are the same color Notice that this program uses a forward declaration also called a forward reference for the class Cylinder This is necessary because the declaration of sameColor inside Cube refers to Cylinder before it is declare
107. important differences between C and Java C which employ a strict object model in which every program is to at least a small extent object oriented C gives you the option Furthermore for the most part the object oriented features of C are transparent at runtime so little if any overhead is incurred CRITICAL SKILL 1 4 A First Simple Program Now it is time to begin programming Let s start by compiling and running the short sample C program shown here jk This is a simple C program Call this file Sample cpp s include lt iostream gt using namespace std A C program begins at main int main cout lt lt C 1S power programming return 0 You will follow these three steps 1 Enter the program 2 Compile the program 3 Run the program Before beginning let s review two terms source code and object code Source code is the human readable form of the program It is stored in a text file Object code is the executable form of the program created by the compiler 10 C A Beginner s Guide by Herbert Schildt Entering the Program The programs shown in this book are available from Osborne s web site www osborne com However if you want to enter the programs by hand you are free to do so Typing in the programs yourself often helps you remember the key concepts If you choose to enter a program by hand you must use a text editor not a word processor Word processors
108. in types For example the lt lt and gt gt operators as applied to cout and cin have little in common with the same operators applied to integer types However for the purposes of the structure and readability of your code an overloaded operator should reflect when possible the spirit of the operator s original use For example the relative to ThreeD is conceptually similar to the relative to integer types There would be little benefit in defining the operator relative to some class in such a way that it acts more the way you would expect the operator for instance to perform The central concept here is that although you can give an overloaded operator any meaning you like for clarity it is best when its new meaning is related to its original meaning Ask the Expert Q Are there any special issues to consider when overloading the relational operators A Overloading a relational operator such as or lt is a straightforward process However there is one small issue As you know an overloaded operator function often returns an object of the class for which it is overloaded However an overloaded relational operator typically returns true or false This is 43 C A Beginner s Guide by Herbert Schildt in keeping with the normal usage of relational operators and allows the overloaded relational operators to be used in conditional expressions The same rationale applies when overloading the logical operators T
109. is the reason that most of the programs in this book have included the following statement using namespace std This causes the std namespace to be brought into the current namespace which gives you direct access to the names of the functions and classes defined within the library without having to qualify each one with std Of course you can explicitly qualify each name with std if you like For example you could explicitly qualify cout like this std cout lt lt Explicitly qualify cout with std You may not want to bring the standard C library into the global namespace if your program will be making only limited use of it or if doing so will cause name conflicts However if your program contains hundreds of references to library names then including std in the current namespace is far easier than qualifying each name individually Progress Check 1 What is anamespace What keyword creates one 2 Are namespaces additive 3 What does using do 41 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 12 6 static Class Members You learned about the keyword static in Module 7 when it was used to modify local and global variable declarations In addition to those uses static can be applied to members of a class Both variables and function members can be declared static Each is described here static Member Variables When you precede a member variable s declaration with static you are telling the co
110. it is not a string Thus the preceding code will display the numeric value of train not the string train Actually to create code that inputs and outputs enumeration symbols as strings is quite tedious For example the following code is needed in order to display in words the kind of transportation that how contains switch how case car cout lt lt Automobile break case truck cout lt lt Truck break case airplane cout lt lt Airplane break case train cout lt lt Train break case boat cout lt lt Boat break Sometimes it is possible to declare an array of strings and use the enumeration value as an index in order to translate the value into its corresponding string For example the following program prints the names of three types of transportation 14 C A Beginner s Guide by Herbert Schildt Demonstrate an enumeration include lt iostream gt using namespace std enum transport car truck airplane train boat char name 20 Automobile Truck Airplane Train Boat ii int mair l transport how how car e Use an enumeration cout lt lt name how lt lt n value to index an array how airplane cout lt lt name how lt lt n how train cout lt lt nane how lt lt n return 0 The output is shown here Automobile Airplane Train The approach used by this program to convert
111. its class In this case you must use the object s name and the dot operator For example this calls range on minivan 7 C A Beginner s Guide by Herbert Schildt range minivan range The invocation minivan range causes range to operate on minivan s copy of the instance variables Thus it returns the range for minivan The second way a member function can be called is from within another member function of the same class When one member function calls another member function of the same class it can do so directly without using the dot operator In this case the compiler already knows which object is being operated upon It is only when a member function is called by code that does not belong to the class that the object name and the dot operator must be used The program shown here puts together all the pieces and missing details and illustrates the range function A program that uses the Vehicle class include lt iostream gt using namespace std Declare the Vehicle class class Vehicle public int passengers number of passengers int fuelcap fuel capacity in gallons int mpg fuel consumption in miles per gallon int range compute and return the range Declare range ti Implement the range member function int Vehicle range w Implement range return mpg fuelcap int main Vehicle minivan create a Vehicle object Vehicle sportscar
112. keywords true and false Since it is common to refer to the oct dec and hex fields they can be collectively referred to as basefield Similarly the left right and internal fields can be referred to as adjustfield Finally the scientific and fixed fields can be referenced as floatfield Setting and Clearing Format Flags To set a flag use the setf function This function is a member of ios Its most common form is shown here fmtflags setf fmtflags flags This function returns the previous settings of the format flags and turns on those flags specified by flags For example to turn on the showbase flag you can use this statement 11 C A Beginner s Guide by Herbert Schildt stream setf ios showbase Here stream is the stream you want to affect Notice the use of ios to qualify showbase Because showbase is an enumerated constant defined by the ios class it must be qualified by ios when it is referred to This principle applies to all of the format flags The following program uses setf to turn on both the showpos and scientific flags Use setf include lt iostream gt using namespace std int main Turn on showpos and scientific flags cout setf ios showpos ey ee TEE if cout setf ios scientific ee cout lt lt 123 lt lt lt lt 123 23 lt lt return 0 The output produced by this program is shown here 123 1 232300e 002 You can OR together as many flags as
113. like other types of pointers ob show_num p amp eb assign p the address of p gt set_num 20 call functions through a pointer to ob p gt show_num Notice the use of the arrow operator return 0 Notice that the address of ob is obtained using the amp address of operator in the same way that the address is obtained for any type of variable As you know when a pointer is incremented or decremented it is increased or decreased in such a way that it will always point to the next element of its base type The same thing occurs when a pointer to an object is incremented or decremented the next object is pointed to To illustrate this the preceding program has been modified here so that ob is a two element array of type P_example Notice how p is incremented and decremented to access the two elements in the array Inerementing and decrementing an object pointer include lt iostream gt using namespace std class P_example int num 35 C A Beginner s Guide by Herbert Schildt public void set_num int val num val void show_num cout lt lt num lt lt n int main P_example ob 2 p ob 0 set_num 10 access objects directly ob 1 set_num 20 p amp ob 0 obtain pointer to first element p gt show_num show value of ob 0 using pointer p advance to next object p gt show_num show value of ob 1 using pointer p retreat to
114. link your program The solution to this dilemma is to declare all of the global variables in one file and use extern declarations in the others as shown in Figure 7 1 File One declares x y and ch In File Two the global variable list is copied from File One and the extern specifier is added to the declarations The extern specifier allows a variable to be made known to a module but does not actually create that variable In other words extern lets the compiler know what the types and names are for these global variables without actually creating storage for them again When the linker links the two modules together all references to the external variables are resolved While we haven t yet worried about the distinction between the declaration and the definition of a variable it is important here A declaration declares the name and type of a variable A definition causes storage to be allocated for the variable In most cases variable declarations are also definitions However by preceding a variable name with the extern specifier you can declare a variable without defining it 5 C A Beginner s Guide by Herbert Schildt File One File Two int x extern int x y char ch extern char ch int main void func22 ff aa x y 10 void funcl void func23 x 123 y 10 A variation on extern provides a linkage specification which is an instruction to the compiler about how a function is to be
115. lt 1 is less than 4 break case d cout lt lt break i is 4 In this fragment if i has the value 1 2 or 3 then the message iis less than 4 is displayed If it is 4 then iis 4 is displayed The stacking of cases as shown in this example is very common when several cases share common code Nested switch Statements It is possible to have a switch as part of the statement sequence of an outer switch Even if the case constants of the inner and outer switch contain common values no conflicts will arise For example the following code fragment is perfectly acceptable switch chl case A cout lt lt This A is part of outer switch switch ch23 1 t A nested switch case A cout lt lt This A is part of inner switch break case E break case B Progress Check 10 C A Beginner s Guide by Herbert Schildt 1 The expression controlling the switch must be of what type 2 When the switch expression matches a case constant what happens 3 When a case sequence is not terminated by a break what happens Answer Key Q Under what conditions should use an if else if ladder rather than a switch when coding a multiway branch A In general use an if else if ladder when the conditions controlling the selection process do not rely upon a single value For example consider the following if else if sequence if x lt 10 else if y gt 0 else if
116. lt Duplicate lt lt nums i lt lt n return 0 4 Anull terminated string is an array of characters that ends with a null 5 gnore case when comparing strings include lt iostream gt include lt cctype gt using namespace std int main char str1i 80 char str2 80 char pl p2 cout lt lt Enter first string cin gt gt strl cout lt lt Enter second string cin gt gt str2 strl str 2 pl p2 g C A Beginner s Guide by Herbert Schildt loop as long as pl and p2 point to non null characters while pl amp amp p2 1f tolower pl tolower p2 break else pl p2 strings are the same if both pl and p2 point to the null terminator ad 1 pl amp amp p2 cout lt lt Strings are the same except for lt lt Dossible case differences n else cout lt lt Strings differ n return 0 6 When using strcat the recipient array must be large enough to hold the contents of both strings 7 Ina multidimensional array each index is specified within its own set of brackets 8 int nums 5 66 88 9 Anunsized array declaration ensures that an initialized array is always large enough to hold the initializers being specified 10 A pointer is an object that contains a memory address The pointer operators are amp and 11 Yes a pointer can be indexed like an array Yes an array can be accessed through a pointe
117. lt lt cout lt lt cout lt lt break case 2 cout lt lt cout lt lt cout lt lt cout lt lt cout lt lt cout lt lt cout lt lt break default cout lt lt The 1if n n 1f condition statement n else statement n The switch n n switch expression n case constant n i statement sequencen break n ff saarni n Selection not found n Notice how the default clause catches invalid choices For example if the user enters 3 no case constants will match causing the default sequence to execute 5 Here is the entire Help cpp program listing i Project 3 1 A simple help system tinclude lt iostream gt using namespace std int mairt char choice cout lt lt Help on n cout lt lt cout lt lt cout lt lt Choose one e L1 if n 2 switch n f cin gt gt choice 12 C A Beginner s Guide by Herbert Schildt cout lt lt yn swiltch choice case l1 cout lt lt The if n n cout lt lt 1i1f condition statement n cout lt lt else statement n break case 2 cout lt lt The switch n n cout lt lt switch expression n cout lt lt case constant n cout lt lt statement sequence n cout lt lt break n cout lt lt ff m cout lt lt n break default cout lt lt Selection not found n return 0
118. lt lt myfunc 88 lt lt Error ambiguous Should 88 be converted to return 0 z char or unsigned char char myfunc unsigned char ch return ch 1 char myfunc char ch return ch 1 In C unsigned char and char are not inherently ambiguous They are different types However when myfunc is called with the integer 88 the compiler does not know which function to call That is should 88 be converted into a char or unsigned char Both are valid conversions Another way you can cause ambiguity is by using default arguments in an overloaded function To see how examine this program 31 C A Beginner s Guide by Herbert Schildt More function overloading ambiguity include lt iostream gt using namespace std int myfunc int i int myfunc int i int j 1 int main cout lt lt myfunc 4 5 lt lt unambiguous cout lt lt myfunc 10 Error ambiguous return 0 Here is defaulting or is the single parameter version of mytunc being invoked int myfunc int i return i In the first call to myfunc two arguments are specified therefore no ambiguity is introduced and myfunc int i int j is called However the second call to myfunc results in ambiguity because the compiler does not know whether to call the version of myfunc that takes one argument or to apply the default to the version that takes two arguments As you continue to writ
119. message by XORing the characters in that message To encode the XOR operation is applied the first time yielding the ciphertext To decode the XOR is applied a second time yielding the plaintext Here is a simple example that uses this approach to encode and decode a short message Use XOR to encode and decode a message include lt iostream gt using namespace std int main char msg This is a test 20 C A Beginner s Guide by Herbert Schildt char key 88 cout lt lt Original message lt lt msg lt lt n for int i 0 i lt strlen msgq i msg i msg i key ___ _ _ This constructs the encoded string cout lt lt Encoded message lt lt msg lt lt n for int i 0 i lt strlen msq i msg i msg i key io This constructs a decoded string cout lt lt Decoded message lt lt msg lt lt n return OQ Here is the output Original message This is a test Encoded message O1 x1 x9x Decoded message This is a test As the output proves the result of two XORs using the same key produces the decoded message The unary one s complement NOT operator reverses the state of all the bits of the operand For example if some integer called A has the bit pattern 1001 0110 then A produces a result with the bit pattern 0110 1001 The following program demonstrates the NOT operator by displaying a number and its complement
120. n n cout lt lt continue n break case B cout lt lt The goto n n cout lt lt goto label n break cout lt lt n Show the help menu 13 C A Beginner s Guide by Herbert Schildt void Help cout lt lt cout lt lt cout lt lt cout lt lt cout lt lt cout lt lt cout lt lt cout lt lt cout lt lt cout lt lt Return bool Help i1f ch lt Showmenu Help on n 1 if n switch n for n while n do while n break n continue n B goto n Choose one q to quit om ie W bo true if a selection is valid sisvalid char ch 1 ch gt 8 amp amp ch q return false else return true int main char choice Help hlpob create an instance of the Help class Use the Help object to display information for f do hilpob showmenu cin gt gt choice while hlpob isvalid choice 1f choice q break cout lt lt n hlpob helpon choice return 0 When you try the program you will find that it is functionally the same as in Module 3 The advantage to this approach is that you now have a help system component that can be reused whenever it is needed CRITICAL SKILL 8 4 Constructors and Destructors In the preceding examples the instance variables of each Vehicle object had to be set manually by use of a sequence of stateme
121. not reinvent those elements The separation of interface and implementation also allows the creation of class libraries which can be provided by a third party If these libraries are implemented correctly they will provide a common interface that you can use to derive classes of your own that meet your specific needs For example both the Microsoft Foundation Classes MFC and the newer NET Framework Windows Forms class library support Windows programming By using these classes your program can inherit much of the 33 C A Beginner s Guide by Herbert Schildt functionality required by a Windows program You need add only the features unique to your application This is a major benefit when programming complex systems Applying Virtual Functions To better understand the power of virtual functions we will apply it to the TwoDShape class In the preceding examples each class derived from TwoDShape defines a function called area This suggests that it might be better to make area a virtual function of the TwoDShape class allowing each derived class to override it defining how the area is calculated for the type of shape that the class encapsulates The following program does this For convenience it also adds a name field to TwoDShape This makes it easier to demonstrate the classes Use virtual functions and polymorphism tinclude lt iostream gt include lt cstring gt using namespace std A class for two di
122. of code in which they are declared is executing A local variable is created when its declaration statement is encountered within its block and destroyed when the block is left Because a local variable is destroyed upon exit from its block its value is lost The most common code block in which variables are declared is the function Each function defines a block of code that begins with the function s opening curly brace and ends with its closing curly brace A function s code and data are private to that function and cannot be accessed by any statement in any other function except through a call to that function It is not possible for instance to use a goto statement to jump into the middle of another function 11 C A Beginner s Guide by Herbert Schildt The body of a function is hidden from the rest of the program and it can neither affect nor be affected by other parts of the program Thus the contents of one function are completely separate from the contents of another Stated another way the code and data that are defined within one function cannot interact with the code or data defined in another function because the two functions have a different scope Because each function defines its own scope the variables declared within one function have no effect on those declared in another even if those variables share the same name For example consider the following program include lt iostream gt using namespace std 4
123. of the I O class hierarchies one for 8 bit characters and one for wide characters This book discusses only the 8 bit character classes since they are by far the most frequently used Here is a list of the mapping of template class names to their character based versions Template Class Name Equivalent Character Based Class Name basic_streambutf streambut basic_ios ios basic_istream istream basic_ostream ostream basic_iostream lostream basic_fstream fstream basic_ifstream itstream basic_ofstream ofstream The character based names will be used throughout the remainder of this book since they are the names that you will use in your programs They are also the same names that were used by the old I O library This is why the old and the new I O library are compatible at the source code level One last point The ios class contains many member functions and variables that control or monitor the fundamental operation of a stream It will be referred to frequently Just remember that if you include lt iostream gt in your program you will have access to this important class Progress Check 1 What is a stream What is a file 2 What stream is connected to standard output 3 C I O is supported by a sophisticated set of class hierarchies True or false CRITICAL SKILL 11 3 Overloading the I O Operators In the preceding modules when a program needed to output or input the data associated with a class member functions were cre
124. pow returns the value of base raised to the exp power The arguments to pow are double values and pow returns a value of type double Step by Step 1 Create a new file called RegPay cpp 2 Here are the variables that will be used by the program double Principal original principal double IntRate interest rate such as 0 075 double PayPerYear number of payments per year double NumYears number of years double Payment the regular payment double numer denom temporary work variables double b e base and exponent for call to pow Notice how each variable declaration is followed by a comment that describes its use This helps anyone reading your program understand the purpose of each variable Although we won t include 29 C A Beginner s Guide by Herbert Schildt such detailed comments for most of the short programs in this book it is a good practice to follow as your programs become longer and more complicated Add the following lines of code which input the loan information cout lt lt Enter principal Gin gt gt Principa cout lt lt Enter interest rate 1 e 0 075 Cin gt gt IntRate cout lt lt Enter number of payments per year Cin gt gt PayPeryYear cout lt lt Enter number of years Cin gt gt NumYears Add the lines that perform the financial calculation numer IntRate Principal PayPerYear e PayPerYear NumYears b
125. precision Table 2 1 All Numeric Data Types Defined by C and Their Minimum Guaranteed Ranges as Specified by the ANSI ISO C Standard It is important to understand that minimum ranges shown in Table 2 1 are just that minimum ranges A C compiler is free to exceed one or more of these minimums and most compilers do Thus the ranges of the C data types are implementation dependent For example on computers that use two s complement arithmetic which is nearly all an integer will have a range of at least 32 768 to 32 767 In all cases however the range of a short int will be a subrange of an int which will be a subrange of a long int The same applies to float double and long double In this usage the term subrange means a range narrower than or equal to Thus an int and long int can have the same range but an int cannot be larger than a long int Since C specifies only the minimum range a data type must support you should check your compiler s documentation for the actual ranges supported For example Table 2 2 shows typical bit widths and ranges for the C data types in a 32 bit environment such as that used by Windows XP Let s now take a closer look at each data type 3 C A Beginner s Guide by Herbert Schildt Type Bit Width Typical Range char 128 to 127 unsigned char O fo 255 siqned char 128 to 127 int 147 483 648 to 27 147 483 6547 unsigned int 147 483 448 to 2 1 47 483 647 signed int O
126. program does not allow lines longer than 80 characters The test for a permissible number of periods is performed inside the loop s conditional expression not outside of it 20 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std int main int len cout lt lt Enter length 1 to 79 cin gt gt len while len gt 0 amp amp len lt 80 cout lt lt png len return 0 If len is out of range then the while loop will not execute even once Otherwise the loop executes until len reaches zero There need not be any statements at all in the body of the while loop Here is an example while rand 100 This loop iterates until the random number generated by rand equals 100 CRITICAL SKILL 3 5 The do while Loop The last of C s loops is the do while Unlike the for and the while loops in which the condition is tested at the top of the loop the do while loop checks its condition at the bottom of the loop This means that a do while loop will always execute at least once The general form of the do while loop is do statements while condition Although the braces are not necessary when only one statement is present they are often used to improve readability of the do while construct thus preventing confusion with the while The do while loop executes as long as the conditional expression is true The following program loops until the number 1
127. range cout lt lt i lt 2 lt lt 7 of a signed short int Thus it will be interpreted as a negative value when assigned to i return The output from this program is shown here 5536 60000 These values are displayed because the bit pattern that represents 60 000 as a short unsigned integer is interpreted as 5 536 as short signed integer assuming 16 bit short integers C allows a shorthand notation for declaring unsigned short or long integers You can simply use the word unsigned short or long without the int The int is implied For example the following two statements both declare unsigned integer variables unsigned x unsigned int y 5 C A Beginner s Guide by Herbert Schildt Characters Variables of type char hold 8 bit ASCII characters such as A z or G or any other 8 bit quantity To specify a character you must enclose it between single quotes Thus this assigns X to the variable ch char ch ch X You can output a char value using a cout statement For example this line outputs the value in ch Cout lt lt This 18 che lt lt ch This results in the following output This is Gh X The char type can be modified with signed or unsigned Technically whether char is signed or unsigned by default is implementation defined However for most compilers char is signed In these environments the use of signed on char is also redundant For the rest of this book it will be ass
128. return 1 out lt lt 10 lt lt lt lt 123 23 lt lt n lt Output to the file out lt lt This is a short text file out close Close the file return OQ The following program reads an integer a float a character and a string from the file created by the previous program 23 C A Beginner s Guide by Herbert Schildt Read from file include lt iostream gt include lt fstream gt using namespace std int main char ch int i Float f char str 80 1fstream in test lt Open a file for text input i1f in f cout lt lt Cannot open file n return 1 in gt gt i in gt gt f in ss dhi Read from the file in gt gt str cout lt lt 1 lt lt lt lt lt lt lt lt ch lt lt n cout lt lt str in close Close the file return Keep in mind that when the gt gt operator is used for reading text files certain character translations occur For example whitespace characters are omitted If you want to prevent any character translations you must open a file for binary access Also remember that when gt gt is used to read a string input stops when the first whitespace character is encountered Ask the Expert Q As you explained in Module 1 C is a superset of C know that C defines an I O system of its own Is the C I O system available to C programmers If so shou
129. returned Thus getloc always indicates the location of the last element retrieved 6 Here is the entire Queue cpp program p Project 8 32 A queue class for characters include lt iostream gt using namespace std const int maxQsize 100 class Queue char q maxQsize this array holds the queue int size Maximum number of elements the queue can store int putloc getloc the put and get indices public Construct a queue of a specific length Queue int len Queue must be less than max and positive 1f len gt maxQOsize len maxQsize else if len lt 0 len 1 size len putloc getloc 0 Put a character into the queue void put char ch f 1f putloc size cout lt lt Queue is full n return putloc qgiputloc ch 29 C A Beginner s Guide by Herbert Schildt Get a character from the queue char get if getloc putloc cout lt lt Queue is empty n return getloc return q getloc Demonstrate the Queue class int main Queue bigd 100 Queue smallQ 4 char ch int i cout lt lt Using bigO to store the alphabet n put some numbers into big for i 0 i lt 26 i bigQ put A i retrieve and display elements from big cout lt lt Contents of bigQ for i 0 i lt 26 i ch bigQ get if ch 0 cout lt lt ch cout lt lt n n cout lt lt
130. same as the previous version An Initialization Alternative If a constructor takes only one parameter then you can use an alternative method to initialize it Consider the following program An alternate initialization method tinclude lt iostream gt using namespace std class MyClass public int x Declare constructor and destructor MyClass int i constructor MyClass destructor a Implement a parameterized constructor MyClass MyClass int i f xX 1 f Implement MyClass destructor MyClass MyClass cout lt lt Destructing object whose x value is lt lt x lt lt n int main MyClass ob 5 calls MyClass 5 lla uc initializing an object cout lt lt ob x lt lt n return OQ Here the constructor for MyClass takes one parameter Pay special attention to how ob is declared in main It uses this declaration MyClass ob 5 In this form of initialization 5 is automatically passed to the i parameter in the MyClass constructor That is the declaration statement is handled by the compiler as if it were written like this MyClass ob 5 71 C A Beginner s Guide by Herbert Schildt In general any time that you have a constructor that requires only one argument you can use either ob x or ob x to initialize an object The reason is that whenever you create a constructor that takes one argument you are also implicitly creating
131. set union Set operator Set ob2 set difference i Return the index of the element specified by ch or 1 if not found int Set find char ch int i for 1i1 0 1 lt len i if members i ch return i return l1 Show the set void Set showset cout c m for int i 0 i lt len i 50 C A Beginner s Guide by Herbert Schildt cout lt lt members i lt lt 3 cout lt lt n Return true if ch is a member of the set Return false otherwise bool Set isMember char ch 1f find ch 1 return true return false Add a unique element to a set Set Set operator char ch Set newset 1f len MaxSize f cout lt lt Set is full n return this return existing set newset this duplicate the existing set see if element already exists 1 f find ch 1 if not found then add add new element to new set newset members newset len ch newset len return newset return updated set Remove an element from the set Set Set operator char ch Set newset int i fFind ch 1 will be 1 if element not found copy and compress the remaining elements for int j 0 j lt len j 1f j i newset newset members return newset Set union 51 C A Beginner s Guide by Herbert Schildt Set S et operator Set ob2 Set newset this copy the first set Badd unique
132. set x y and z to 100 This fragment sets the variables x y and z to 100 using a single statement This works because the is an operator that yields the value of the right hand expression Thus the value of z 100 is 100 which is then assigned to y which in turn is assigned to x Using a chain of assignment is an easy way to seta group of variables to a common value CRITICAL SKILL 2 7 Compound Assignments C provides special compound assignment operators that simplify the coding of certain assignment statements Let s begin with an example The assignment statement shown here x x 10 can be written using a compound assignment as x 10 The operator pair tells the compiler to assign to x the value of x plus 10 Here is another example The statement 25 C A Beginner s Guide by Herbert Schildt is the same as x 100 Both statements assign to x the value of x minus 100 There are compound assignment operators for most of the binary operators that is those that require two operands Thus statements of the form var var op expression can be converted into this compound form var op expression Because the compound assignment statements are shorter than their noncompound equivalents the compound assignment operators are also sometimes called the shorthand assignment operators The compound assignment operators provide two benefits First they are more compact than their longhand equivale
133. short value f short is invoked and the automatic conversion to int does not occur 19 C A Beginner s Guide by Herbert Schildt Progress Check 1 When a function is overloaded what condition must be met 2 Why should overloaded functions perform related actions 3 Does the return type of a function participate in overload resolution Create Overloaded Output Functions In this project you will create a collection of overloaded functions that output various data types to the screen Although using cout statements is quite convenient such a collection of output functions offers an alternative that might appeal to some programmers In fact both Java and C use output functions rather than output operators By creating overloaded output functions you can use either method and have the best of both worlds Furthermore you can tailor your output functions to meet your specific needs For example you can make the Boolean values display true or false rather than 1 and O You will be creating two sets of functions called printIn and print The printIn function displays its argument followed by a newline The print function will display its argument but does not append a newline For example print 1 printin X print Function overloading is powerful print 18 22 displays 1X Function overloading is powerful 18 22 In this project print and println will be overloaded for data o
134. short or float value In the case of short C automatically converts it to int Thus f int is invoked In the case of float the value is converted to double and f double is called It is important to understand however that the automatic conversions apply only if there is no direct match between a parameter and an argument For example here is the preceding program with the addition of a version of f that specifies a short parameter 18 C A Beginner s Guide by Herbert Schildt Now add short include lt iostream gt using namespace std void f int x void f short x fishort has void f double x been added int main f int i 10 double d 10 1 short s 99 float r 11 5F E i calls int f d calls f double f s now calls f short Now no type conversion occurs because f short is available E r calls f double type conversion return 0 void f int x f cout lt lt Inside E int lt lt x lt lt n void short x cout lt lt Inside f short lt lt x lt lt n void f double x cout lt lt Inside f double lt lt x lt lt n Now when the program is run the following output is produced Inside f int 10 Inside f double 10 1 Inside f short 99 Inside f double 11 5 In this version since there is a version of f that takes a short argument when f is called with a
135. takes one parameter assigning its value to both x and y The third constructor takes two parameters initializing x and y individually 2 C A Beginner s Guide by Herbert Schildt Overloaded constructors are beneficial for several reasons First they add flexibility to the classes that you create allowing an object to be constructed in a variety of ways Second they offer convenience to the user of your class by allowing an object to be constructed in the most natural way for the given task Third by defining both a default constructor and a parameterized constructor you allow both initialized and uninitialized objects to be created CRITICAL SKILL 9 2 Assigning Objects If both objects are of the same type that is both are objects of the same class then one object can be assigned to another It is not sufficient for the two classes to simply be physically similar their type names must be the same By default when one object is assigned to another a bitwise copy of the first object s data is assigned to the second Thus after the assignment the two objects will be identical but separate The following program demonstrates object assignment Demonstrate object assignment include lt iostream gt using namespace std class Test int a b public void setab int i int j a i b qj void showab cout lt lt a is lt lt a lt lt n cout lt lt bis lt lt b lt lt n If in
136. template lt class X gt void gs X items int left int righ int X X Mo H lol do i J Yi left J right items left right 2 while items i lt x amp amp 1 lt right i while x lt items j amp amp J gt left j if i lt j y items i items i items j items j y i j while i lt jJ if left lt j gs items left J if i lt right gqs items 1i right int main i sort characters char str jfmckldoelazlkper cout lt lt quicksort str strlen str cout lt lt Original order lt lt str lt lt n Sorted order lt lt str lt lt n sort integers int nums 4 3 7 5 9 8 1 3 5 4 cout lt lt for int i 0 i lt 10 i Original order cout lt lt nums i lt lt Ns cout lt lt endl C A Beginner s Guide by Herbert Schildt quicksort nums 10 cout lt lt Sorted order for int i 0 i lt 10 i cout lt lt nums i lt lt cout lt lt endl return 0 7 Here is one way to store Sample objects in a Queue Use Project 12 1 to store Sample objects A template queue class f include lt iostream gt using namespace std class Sample int id public Sample id 0 Sample int x id x void show cout lt lt id lt lt endl I const int max size 100 This
137. terminated strings are widely used because they offer a high level of efficiency and give the programmer detailed control over string operations When a C programmer uses the term string he or she is usually referring to a null terminated string The second type of string defined by C is the string class which is part of the C class library Thus string is not a built in type It provides an object oriented approach to string handling but is not as widely used as the null terminated string Here null terminated strings are examined String Fundamentals When declaring a character array that will hold a null terminated string you need to declare it one character longer than the largest string that it will hold For example if you want to declare an array str that could hold a 10 character string here is what you would write char str 11 Specifying the size as 11 makes room for the null at the end of the string As you learned earlier in this book C allows you to define string constants A string constant is a list of characters enclosed in double quotes Here are some examples hello there like C Mars It is not necessary to manually add the null terminator onto the end of string constants the C compiler does this for you automatically Therefore the string Mars will appear in memory like this EsEIESESED The last string shown is This is called a null string It contains only the null
138. terminator and no other characters Null strings are useful because they represent the empty string Reading a String from the Keyboard The easiest way to read a string entered from the keyboard is to use a char array in a cin statement For example the following program reads a string entered by the user 11 C A Beginner s Guide by Herbert Schildt Using cin to read a string from the keyboard include lt iostream gt using namespace std int main char str 80 cout lt lt Enter a string cin gt gt str read string from keyboard 4 Read a string using cin cout lt lt Here is your string cout lt lt str return OQ Here is asample run Enter a string testing Here is your string testing Although this program is technically correct it will not always work the way that you expect To see why run the program and try entering the string This is a test Here is what you will see Enter a string This is a test Here is your string This When the program redisplays your string it shows only the word This not the entire sentence The reason for this is that the C I O system stops reading a string when the first whitespace character is encountered Whitespace characters include spaces tabs and newlines One way to solve the whitespace problem is to use another of C s library functions gets The general form of a call to gets is gets array name To rea
139. that allows one function to be implemented two or more different ways each performing a separate task Function overloading is one way that C supports polymorphism Using a default argument it is possible to specify a value for a parameter that will be automatically used when no corresponding argument is specified We will begin with an explanation of the two ways that arguments can be passed to functions and the implications of both methods An understanding of argument passing is needed in order to understand the reference 1 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 6 1 Know the two approaches to argument passing In general there are two ways that a computer language can pass an argument to a subroutine The first is call by value This method copies the value of an argument into the parameter of the subroutine Therefore changes made to the parameter of the subroutine have no effect on the argument used to call it Call by reference is the second way a subroutine can be passed arguments In this method the address of an argument not its value is copied into the parameter Inside the subroutine this address is used to access the actual argument specified in the call This means that changes made to the parameter will affect the argument used to call the subroutine CRITICAL SKILL 6 2 How C Passes Arguments By default C uses call by value for passing arguments This means that the code inside a function ca
140. that it contains and the code that operates on that data While very simple classes might contain only code or only data most real world classes contain both 1 C A Beginner s Guide by Herbert Schildt Data is contained in instance variables defined by the class and code is contained in functions The code and data that constitute a class are called members of the class CRITICAL SKILL 8 1 The General Form of a Class A class is created by use of the keyword class The general form of a simple class declaration is class class name private data and functions public public data and functions object list Here class name specifies the name of the class This name becomes a new type name that can be used to create objects of the class You can also create objects of the class by specifying them immediately after the class declaration in object list but this is optional Once a class has been declared objects can be created where needed A class can contain private as well as public members By default all items defined in a class are private This means that they can be accessed only by other members of their class and not by any other part of your program This is one way encapsulation is achieved you can tightly control access to certain items of data by keeping them private To make parts of a class public that is accessible to other parts of your program you must declare them after the public keyword All variab
141. that might prevent the compiler from complying with the request Here are some examples e Some compilers will not generate inline code if a function contains a loop a switch ora goto 23 C A Beginner s Guide by Herbert Schildt e Often you cannot have inline recursive functions e Inline functions that contain static variables are frequently disallowed Remember Inline restrictions are implementation dependent so you must check your compiler s documentation to find out about any restrictions that may apply in your situation Creating Inline Functions Inside a Class The second way to create an inline function is by defining the code to a member function inside a class definition Any function that is defined inside a class definition is automatically made into an inline function It is not necessary to precede its declaration with the keyword inline For example the preceding program can be rewritten as shown here include lt iostream gt using namespace std class cl int i private by default public Automatic inline functions int get_i return i Define get_i and void put_i int j i 4 _ put if inside their class j int main cl s s put_i 10 cout lt lt s get_i return OQ Notice the way the function code is arranged For very short functions this arrangement reflects common C style However you could write them as shown here 24 C A Beginner s G
142. the following Vehicle minivan create a Vehicle object called minivan After this statement executes minivan will be an instance of Vehicle Thus it will have physical reality Each time you create an instance of a class you are creating an object that contains its own copy of each instance variable defined by the class Thus every Vehicle object will contain its own copies of the instance variables passengers fuelcap and mpg To access these variables you will use the dot operator The dot operator links the name of an object with the name of a member The general form of the dot operator is shown here object member Thus the object is specified on the left and the member is put on the right For example to assign the fuelcap variable of minivan the value 16 use the following statement minivan fuelcap 16 In general you can use the dot operator to access instance variables and call functions Here is a complete program that uses the Vehicle class 3 C A Beginner s Guide by Herbert Schildt A program that uses the Vehicle class include lt iostream gt using namespace std Declare the Vehicle class class Vehicle Declare the Vehicle class public int passengers number of passengers int fuelcap fuel capacity in gallons int mpg Euel consumption in miles per gallon Create an instance of Vehicle called minivan int main Vehicle minivan create a Vehicle t
143. the plus operator This means that the operation is first performed on the 1 and that the result is added to 9 which of course does not equal 0 This causes the EVEN macro to improperly report the value of 9 1 as odd To fix the problem there must be parentheses around a in the macro definition of EVEN as is shown in this corrected version of the program This program is now fixed include lt iostream gt using namespace std define EVEN a a 2 0 P 1 0 int main L EVEN 941 cout lt lt is even else cout lt lt is odd return 0 Now the 9 1 is evaluated prior to the modulus operation and the resulting value is properly reported as even In general it is a good idea to surround macro parameters with parentheses to avoid unforeseen troubles like the one just described The use of macro substitutions in place of real functions has one major benefit Because macro substitution code is expanded inline no overhead of a function call is incurred so the speed of your program increases However this increased speed might be paid for with an increase in the size of the program due to duplicated code Although still commonly seen in C code the use of function like macros has been rendered completely redundant by the inline specifier which accomplishes the same goal better and more safely Remember inline causes a function to be expanded inline rather than called Also inline functions do not requi
144. the program stop when the user enters a period At the end have the program display the number of case changes that have taken place 12 What is C s unconditional jump statement 37 C A Beginner s Guide by Herbert Schildt Module 4 Arrays Strings and Pointers Table of Contents CRITICAL SKILL 4 1 Use one dimensional arrays CRITICAL SKILL 4 2 Two Dimensional Arrays CRITICAL SKILL 4 3 Multidimensional Arrays CRITICAL SKILL 4 4 Strings CRITICAL SKILL 4 5 Some String Library Functions CRITICAL SKILL 4 6 Array Initialization CRITICAL SKILL 4 7 Arrays of Strings CRITICAL SKILL 4 8 Pointers CRITICAL SKILL 4 9 The Pointer Operators CRITICAL SKILL 4 10 Pointer Expressions CRITICAL SKILL 4 11 Pointers and Arrays CRITICAL SKILL 4 12 Multiple Indirection This module discusses arrays strings and pointers Although these may seem to be three disconnected topics they aren t In C they are intertwined and an understanding of one aids in the understanding of the others An array is a collection of variables of the same type that are referred to by a common name Arrays may have from one to several dimensions although the one dimensional array is the most common Arrays offer a convenient means of creating lists of related variables The array that you will probably use most often is the character array because it is used to hold a character string The C language does not define a built in string data type In
145. their parameter declarations are different In this situation the functions that share the same name are said to be overloaded and the process is referred to as function overloading Function overloading is one way that C achieves polymorphism In general to overload a function simply declare different versions of it The compiler takes care of the rest You must observe one important restriction the type and or number of the parameters of each overloaded function must differ It is not sufficient for two functions to differ only in their return types They must differ in the types or number of their parameters Return types do not provide sufficient information in all cases for C to decide which function to use Of course overloaded functions may differ in their return types too When an overloaded function is called the version of the function whose parameters match the arguments is executed 13 C A Beginner s Guide by Herbert Schildt Let s begin with a short sample program Overload a function three times include lt iostream gt using namespace std void f int i integer parameter void f int i int j two integer parameters void f double k one double parameter A separate prototype Is needed for each version of int main 0 an overloaded function 10 f call int 10 20 gf call f int int f 12 23 call double return QQ void int i cout lt lt In f int
146. this result is true then at least one of the operands is true Next p is ANDed with q This result is true if both operands are true This result is then inverted using the NOT operator Thus the outcome of p amp amp q will be true when either p q or both are false Finally this result is ANDed with the result of p q Thus the entire expression will be true when one but not both operands is true 3 Here is the entire XOR cpp program listing It demonstrates the XOR operation for all four possible combinations of true false values Project 2 2 Create an XOR using the C logical operators ae include lt iostream gt include lt cmath gt using namespace std int main DoOol p G7 p true 23 C A Beginner s Guide by Herbert Schildt g Crue COUL lt lt p lt lt KOR T lt G lt lt T ae T ax p I q amp amp p amp amp q lt lt n p false q true Gout lt lt gt lt lt M KOR T lt Oo mc as M xe p Il q amp amp p amp amp q lt lt n D Crue q false COUL lt lt D lt lt T XOR M lt lt g lt lt T ae T as p Il q amp amp p amp amp g lt lt n p false q false Cout lt lt P a E OR m lt a g LL T ing U a lt p TI q amp amp p amp amp q lt lt Tmn return 0 4 Compile and run the program The following output is produced XOR 1 185 XOR 1 15 XOR O 1s XOR 0 18
147. to count and finally assigns var the value produced by the entire comma expression which is 20 The parentheses are necessary because the comma operator has a lower precedence than the assignment operator To actually see the effects of the comma operator try running the following program 31 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std int main int i j 10 Lja II i j j 100 999 j The comma means do this and this and this cout lt lt i return 0 This program prints 1010 on the screen Here is why j starts with the value 10 j is then incremented to 11 Next j is added to 100 Finally j still containing 11 is added to 999 which yields the result 1010 Essentially the comma s effect is to cause a sequence of operations to be performed When it is used on the right side of an assignment statement the value assigned is the value of the last expression in the comma separated list You can in some ways think of the comma operator as having the same meaning that the word and has in English when used in the phrase do this and this and this Progress Check 1 Given this expression x 10 gt 11 1 0 what is the value of x after the expression evaluates 2 The operator is called a ternary operator because it has operands 3 What does the comma do Multiple Assignments C allows a convenient method of
148. total originally had the value 3 200 then val will have the value 3 200 because that is the value stored at location 100 the memory address that was assigned to ptr The operation of can be remembered as at address In this case then the statement could be read as val receives the value at address ptr The following program executes the sequence of the operations just described include lt iostream gt using namespace std int main int total int ptr int val total 3200 assign 3 200 to total ptr amp total get address of total val ptr get value at that address cout lt lt Total is lt lt val lt lt n return 0 I 24 C A Beginner s Guide by Herbert Schildt It is unfortunate that the multiplication symbol and the at address symbol are the same This fact sometimes confuses newcomers to the C language These operators have no relationship to each other Keep in mind that both amp and have a higher precedence than any of the arithmetic operators except the unary minus with which they have equal precedence The act of using a pointer is often called indirection because you are accessing one variable indirectly through another variable Progress Check 1 What is a pointer 2 Show how to declare a long int pointer called valPtr 3 As they relate to pointers what do the and amp operators do The Base Type of a Pointer Is Important In the preced
149. types in order for one to be assigned to another you can override this restriction at your own risk using a cast For example the following fragment is now technically correct 25 C A Beginner s Guide by Herbert Schildt int p double f p int amp f Now technically OK The cast to int causes the double pointer to be converted to an integer pointer However to use a cast for this purpose is questionable practice The reason is that the base type of a pointer determines how the compiler treats the data it points to In this case even though p is actually pointing to a floating point value the compiler still thinks that p is pointing to an int because p is an int pointer To better understand why using a cast to assign one type of pointer to another is not usually a good idea consider the following short program This program will not work right include lt iostream gt using namespace std int main double x y int p x 123 23 p int amp x use cast to assign double to int y p What will this do These statements won t cout lt lt y What will this print yield the desired results return OQ Here is the output produced by the program You might see a different value 1 37439e 009 This value is clearly not 123 23 Here is why In the program p which is an integer pointer has been assigned the address of x which is a double Thus when
150. typically store format information along with text This format information will confuse the C compiler If you are using a Windows platform then you can use WordPad or any other programming editor that you like The name of the file that holds the source code for the program is technically arbitrary However C programs are normally contained in files that use the file extension cpp Thus you can call a C program file by any name but it should use the cpp extension For this first example name the source file Sample cpp so that you can follow along For most of the other programs in this book simply use a name of your own choosing Compiling the Program How you will compile Sample cpp depends upon your compiler and what options you are using Furthermore many compilers such as Microsoft s Visual C Express Edition which you can download for free provide two different ways for compiling a program the command line compiler and the Integrated Development Environment IDE Thus it is not possible to give generalized instructions for compiling a C program You must consult your compiler s instructions The preceding paragraph notwithstanding if you are using Visual C then the easiest way to compile and run the programs in this book is to use the command line compilers offered by these environments For example to compile Sample cpp using Visual C you will use this command line C gt cl GX Sample cpp The GX opt
151. use parentheses to make clear the exact order of evaluation both for yourself and for others who may have to figure out your program later For example which of the following two expressions is easier to read 23 C A Beginner s Guide by Herbert Schildt y 3 34 tempt 127 y 3 34 temp 127 x x Project 2 3 Compute the Regular Payments on a Loan In this project you will create a program that computes the regular payments on a loan such as a car loan Given the principal the length of time number of payments per year and the interest rate the program will compute the payment Since this is a financial calculation you will need to use floating point data types for the computations Since double is the most commonly used floating point type we will use it in this project This project also demonstrates another C library function pow To compute the payments you will use the following formula IntRate Principal PayPer Year Payment iiss nA EE EA iol IntRate PayPerYear 1 Naters where IntRate specifies the interest rate Principal contains the starting balance PayPerYear specifies the number of payments per year and NumYears specifies the length of the loan in years Notice that in the denominator of the formula you must raise one value to the power of another To do this you will use pow Here is how you will call it result pow base exp
152. used to assign i the value 10 i 10 In actuality the preceding statement is shorthand for this one this gt i 10 To see the this pointer in action examine the following short program Use the this pointer include lt iostream gt using namespace std class Test f int i public void load i int val this gt i val Same as i val int get_ij return this gt 1 Same as return i 3 int main Test o o load_i 100 cout lt lt o get_i return 0 This program displays the number 100 This example is of course trivial and no one would actually use the this pointer in this way Soon however you will see why the this pointer is important to C programming One other point Friend functions do not have a this pointer because friends are not members of a class Only member functions have a this pointer 27 C A Beginner s Guide by Herbert Schildt Progress Check 1 Can a struct contain member functions 2 What is the defining characteristic of a union 3 To what does this refer CRITICAL SKILL 9 9 Operator Overloading The remainder of this module explores one of C s most exciting and powerful features operator overloading In C operators can be overloaded relative to class types that you create The principal advantage to overloading operators is that it allows you to seamlessly integrate new data types into your pr
153. user enters a q as a menu selection Step by Step 1 Copy Help2 cpp to a new file called Help3 cpp 2 Surround all of the program code with an infinite for loop Break out of this loop using break when a q is entered Since this loop surrounds all of the program code breaking out of this loop causes the program to terminate 3 Change the menu loop as shown here do cout lt lt Help on n 30 C A Beginner s Guide by Herbert Schildt cout lt lt 1 if n cout lt lt 2 switch n cout lt lt 3 forno cout lt lt 4 while n cout lt lt 5 do while n cout lt lt 6 break n cout lt lt 7 continuen cout lt lt 8 goto n cout lt lt Choose one q to quit cin gt gt choice while choice lt 1 choice gt 8 amp amp choice q Notice that this loop now includes the break continue and goto statements It also accepts aq asa valid choice 4 Expand the switch statement to include the break continue and goto statements as shown here case 6 cout lt lt The break n n cout lt lt break n break case J cout lt lt The continue n n cout lt lt continue n break case S cout lt lt The goto n n cout lt lt goto label n break 5 Here is the entire Help3 cpp program listing Project 3 3 The finished Help system that processes multiple requests ai include lt iostream gt
154. will learn how to create a function You will also learn about passing arguments returning values local and global variables function prototypes and recursion Function Fundamentals A function is a subroutine that contains one or more C statements and performs a specific task Every program that you have written so far has used one function main They are called the building blocks of C because a program is a collection of functions All of the action statements of a program are found within functions Thus a function contains the statements that you typically think of as being the executable part of a program Although very simple programs such as many of those shown in this book will have only a main function most programs will contain several functions In fact a large commercial program will define hundreds of functions 1 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 5 1 Know the general form of a function All C functions share a common form which is shown here return type name parameter list body of function Here return type specifies the type of data returned by the function This can be any valid type except an array If the function does not return a value its return type must be void The name of the function is specified by name This can be any legal identifier that is not already in use The parameter list is a sequence of type and identifier pairs separated by commas Para
155. will be compiled otherwise it will be skipped For example A simple if example include lt iostream gt using namespace std define MAX 100 int main if MAX gt 10 cout lt lt Extra memory required n endif ff return 0 This program will display the message on the screen because as defined in the program MAX is greater than 10 This example illustrates an important point The expression that follows the if is evaluated at compile time Therefore it must contain only identifiers that have been previously defined and constants No variables can be used The else directive works in much the same way as the else statement that forms part of the C language it establishes an alternative if the if directive fails The previous example can be expanded to include the else directive as shown here A simple if else example include lt iostream gt using namespace std define MAX 6 int main if MAX gt 10 cout lt lt Extra memory required n else cout lt lt Current memory OK n endif f return 0 6 C A Beginner s Guide by Herbert Schildt In this program MAX is defined to be less than 10 so the if portion of the code is not compiled but the else alternative is Therefore the message Current memory OK is displayed Notice that the else is used to mark both the end of the if block and the beginning of the else block This is necessary bec
156. will not be able to declare it inside the for loop NOTE Whether a variable declared within the initialization portion of a for loop is restricted to that loop or not has changed over time Originally the variable was available after the for but this was changed during the C standardization process Today the ANSI ISO Standard C restricts the variable to the scope of the for loop Some compilers however do not You will need to check this feature in the environment you are using Before moving on you might want to experiment with your own variations on the for loop As you will find it is a fascinating loop Progress Check l Can portions of a for statement be empty 2 Show how to create an infinite loop using for 3 What is the scope of a variable declared within a for statement CRITICAL SKILL 3 4 The while Loop Another loop is the while The general form of the while loop is while expression statement where statement may be a single statement or a block of statements The expression defines the condition that controls the loop and it can be any valid expression The statement is performed while the condition is true When the condition becomes false program control passes to the line immediately following the loop 19 C A Beginner s Guide by Herbert Schildt The next program illustrates the while in a short but sometimes fascinating program Virtually all computers support an extended character set beyond tha
157. will take a closer look at them As you learned variables are declared using this form of statement 15 C A Beginner s Guide by Herbert Schildt type var name where type is the data type of the variable and var name is its name You can declare a variable of any valid type When you create a variable you are creating an instance of its type Thus the capabilities of a variable are determined by its type For example a variable of type bool stores Boolean values It cannot be used to store floating point values Furthermore the type of a variable cannot change during its lifetime An int variable cannot turn into a double variable for example Initializing a Variable You can assign a value to a variable at the same time that it is declared To do this follow the variable s name with an equal sign and the value being assigned This is called a variable initialization Its general form is shown here type var value Here value is the value that is given to var when var is created Here are some examples int count 10 give count an initial value of 10 char ch X s 7 7 initialize ch with the letter X float 1 2F 7 7 f i initialized with 1 2 When declaring two or more variables of the same type using a comma separated list you can give one or more of those variables an initial value For example int a b 8 c 19 d b and c have initializations In this case only b and c are initialized Dynamic In
158. y is assigned the value pointed to by p y receives only four bytes of data and not the eight required for a double value because p is an integer pointer Therefore the cout statement displays not 123 23 but a garbage value instead Assigning Values through a Pointer You can use a pointer on the left hand side of an assignment statement to assign a value to the location pointed to by the pointer Assuming that p is an int pointer this assigns the value 101 to the location pointed to by p p 101 You can verbalize this assignment like this At the location pointed to by p assign the value 101 To increment or decrement the value at the location pointed to by a pointer you can use a statement like this 26 C A Beginner s Guide by Herbert Schildt p The parentheses are necessary because the operator has lower precedence than does the operator The following program demonstrates an assignment through a pointer include lt iostream gt using namespace std int main int p num p num p 100 Assign num the value 100 through p cout lt lt num lt lt p 4 Increment num through p cout lt lt num lt lt p 4 Decrement num through p cout lt lt num lt lt n return 0 The output from the program is shown here 100 101 100 CRITICAL SKILL 4 10 Pointer Expressions Pointers can be used in most C expressions Howe
159. you like in a single call For example by ORing together scientific and showpos as shown next you can change the program so that only one call is made to setf cout setf ios scientific ios showpos To turn off a flag use the unsetf function whose prototype is shown here void unsetf fmtflags flags The flags specified by flags are cleared All other flags are unaffected Sometimes it is useful to know the current flag settings You can retrieve the current flag values using the flags function whose prototype is shown here fmtflags flags This function returns the current value of the flags relative to the invoking stream The following form of flags sets the flag values to those specified by flags and returns the previous flag values fmtflags flags fmtflags flags The following program demonstrates flags and unsetf 12 C A Beginner s Guide by Herbert Schildt Demonstrate flags and unsetf include lt iostream gt using namespace std int main ios fmtflags f f cout flags Get the format flags 1f f amp 1os showpos cout lt lt showpos is set for cout n else cout lt lt showpos is cleared for cout n cout lt lt nSetting showpos for cout n cout setf ios showpos f cout flags Set the showpos flag 1f f amp ios showpos cout lt lt showpos is set for cout n else cout lt lt showpos is cleared for cout n co
160. 0 0101000 1 1010001 0 0100010 1 10001010 000103101 0010101 0 01010100 CRITICAL SKILL 7 9 The Operator One of C s most fascinating operators is the The operator is often used to replace if else statements of this general form 29 C A Beginner s Guide by Herbert Schildt if condition var expression1 else var expression2 Here the value assigned to var depends upon the outcome of the condition controlling the if The is called a ternary operator because it requires three operands It takes the general form Exp1 Exp2 Exp3 where Exp1 Exp2 and Exp3 are expressions Notice the use and placement of the colon The value of a expression is determined like this Exp1 is evaluated If it is true then Exp2 is evaluated and becomes the value of the entire expression If Exp1 is false then Exp3 is evaluated and its value becomes the value of the expression Consider this example which assigns absval the absolute value of val absval val lt 0 val val get absolute value of val Here absval will be assigned the value of val if val is zero or greater If val is negative then absval will be assigned the negative of that value which yields a positive value The same code written using an if else statement would look like this if val lt 0 absval val else absval val Here is another example of the operator This program divides two numbers but will not allow a division by zero
161. 00 379 7 On your own have the program display the total amount of interest paid over the life of the loan Module 2 Mastery Check 1 What type of integers are supported by C 2 By default what type is 12 2 31 C A Beginner s Guide by Herbert Schildt 3 What values can a bool variable have 4 What is the long integer data type 5 What escape sequence produces a tab What escape sequence rings the bell 6 A string is surrounded by double quotes True or false 7 What are the hexadecimal digits 8 Show the general form for initializing a variable when it is declared 9 What does the do Can it be used on floating point values 10 Explain the difference between the prefix and postfix forms of the increment operator 11 Which of the following are logical operators in C a amp amp b C d G e 12 How can x x 12 be rewritten 13 What is a cast 14 Write a program that finds all of the prime numbers between 1 and 100 32 C A Beginner s Guide by Herbert Schildt Module3 Program Control Statements Table of Contents CRITICAL SKILL 3 1 The if Statement CRITICAL SKILL 3 2 The switch Statement CRITICAL SKILL 3 3 The for Loop CRITICAL SKILL 3 4 The while Loop CRITICAL SKILL 3 5 The do while Loop CRITICAL SKILL 3 6 Using break to Exit a Loop CRITICAL SKILL 3 7 Using continue CRITICAL SKILL 3 8 Nested Loops CRITICAL SKILL 3 9 Using the goto Statement Th
162. 00 is entered 71 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std int main int num A do while loop always executes at least once do cout lt lt Enter a number 100 to stop cin gt gt num while num 100 return 0 Using a do while loop we can further improve the Magic Number program This time the program loops until you guess the number Magic Number program 3rd improvement include lt iostream gt include lt cestdlib gt using namespace std int main int magic magic number int guess user s guess magic rand get a random number do f cout lt lt Enter your guess cin gt gt guess if guess magic cout lt lt Right cout lt lt magic lt lt is the magic number n else cout lt lt Serry you re wrong if guess gt magic cout lt lt Your guess is too high n else cout lt lt Your guess is too low n while guess magic return 0 22 C A Beginner s Guide by Herbert Schildt Here is asample run Enter your guess 10 a a Orry you re wrong Your guess is too low Enter your guess 100 50rry you re wrong Your guess is too high Enter your guess 50 Sorry you re wrong Your guess is too high Enter your guess 41 Right 41 is the magic number One last point Like the for and while the body of the do while loop can
163. 10 10b put 20 10b put 30 cout lt lt Contents of integer queue i a for int 1 0 i lt 3 i this will underflow cout lt lt i10a get lt lt cout lt lt endl cout lt lt Contents of integer queue i0b for int 1 0 1 lt 3 i cout lt lt i0b get lt lt cout lt lt endl C A Beginner s Guide by Herbert Schildt Queue lt double gt dQa 10 dOb 10 create two double queues dQa put 1 01 dQa put 2 02 dQa put 3 03 dOb put 10 01 dQb put 20 02 dOb put 30 03 cout lt lt Contents of double queue dOa for int 1 0 1 lt 3 i cout lt lt dOa get lt lt cout lt lt endl cout lt lt Contents of double queue dOb for int i 0 i lt 3 i cout lt lt dOb get lt lt cout lt lt endl catch QExcpt exc cout lt lt exc msqd return 0 5 Ageneric function defines the general form of a routine but does not specify the precise type of data upon which it operates It is created using the keyword template 6 Here is one way to make quicksort and qs into generic functions f A generic Quicksort include lt iostream gt include lt cstring gt using namespace std Set up a call to the actual sorting function template lt class X gt void quicksort X items int len qs items 0 len 1 37 C A Beginner s Guide by Herbert Schildt 38 A generic version of Quicksort
164. 123 lt lt lt lt 123 23 return O The program shown next uses ws to skip any leading whitespace when inputting a string into s Skip leading whitespace include lt iostream gt using namespace std int mair char s 80 cin gt gt wS gt gt g 4 e ws cout lt lt s return 0 CRITICAL SKILL 11 6 Creating Your Own Manipulator Functions You can create your own manipulator functions There are two types of manipulator functions those that take arguments and those that don t The creation of parameterized manipulators requires the use of techniques beyond the scope of this book However the creation of parameterless manipulators is quite easy and is described here All parameterless manipulator output functions have this skeleton ostream amp manip name ostream amp stream your code here return stream Here manip name is the name of the manipulator It is important to understand that even though the manipulator has as its single argument a pointer to the stream upon which it is operating no argument is specified when the manipulator is used in an output expression The following program creates a manipulator called setup that turns on left justification sets the field width to 10 and specifies that the dollar sign will be the fill character 18 C A Beginner s Guide by Herbert Schildt Create an output manipulator include lt iostream gt include lt iomanip gt
165. 1n void ofstream open const char i ename ios openmode mode 1os out 1os trunc void fstream open const char ilename 1os openmode mode ios in 108 o0ut Here filename is the name of the file it can include a path specifier The value of mode determines how the file is opened It must be one or more of the values defined by openmode which is an enumeration defined by ios through its base class ios_ base The values are shown here los app 10s ate ios binary 10s2 1n 10s out 10s trunc You can combine two or more of these values by ORing them together Including ios app causes all output to that file to be appended to the end This value can be used only with files capable of output Including ios ate causes a seek to the end of the file to occur when the file is opened Although ios ate causes an initial seek to end of file I O operations can still occur anywhere within the file The ios in value specifies that the file is capable of input The ios out value specifies that the file is capable of output The ios binary value causes a file to be opened in binary mode By default all files are opened in text mode In text mode various character translations may take place such as carriage return linefeed sequences being converted into newlines However when a file is opened in binary mode no such character translations will occur Understand that any file whether it contains formatted text or raw dat
166. 2 lt lt Hypotenuse of tl hypot cx n E a lt lt Area of tl lt lt area lt lt n lt lt Hypotenuse of t2 hypot ex ie Fee lt lt Area of t2 lt lt area lt lt n return 0 25 lt lt lt C A Beginner s Guide by Herbert Schildt j Enhanced Project 8 1 Add user ID to Help class y include lt iostream gt using namespace std A class that encapsulates a help system class Help int userID public Help int id userID id Help cout lt lt Terminating help for lt lt userID lt lt n int getID return userID void helpon char what void showmenu bool isvalid char ch Le Display help information void Help helpon char what switch what ease l cout lt lt The if n n cout lt lt 1f condition statement n 26 C A Beginner s Guide by Herbert Schildt 27 cout lt lt else statement n break case 2 cout lt lt The switch n n cout lt lt switch expression n cout lt lt case constant n cout lt lt statement sequence n cout lt lt break n cout lt lt ms ae cout lt lt n break case 3 cout lt lt The for n n cout lt lt for init condition increment cout lt lt statement n break case 4 cout lt lt The while n n cout lt lt while condition statement n
167. 3 Are index21 and Index21 the same identifier Answer Key 1 The keyword is for In C all keywords are in lowercase 2 A C identifier can contain letters digits and the underscore 3 No C is case sensitive Module 1 Mastery Check 1 It has been said that C sits at the center of the modern programming universe Explain this statement 2 AC compiler produces object code that is directly executed by the computer True or false 3 What are the three main principles of object oriented programming 4 Where do C programs begin execution 5 What is a header 6 What is lt iostream gt What does the following code do include lt iostream gt 7 What is a namespace 8 What is a variable 9 Which of the following variable names is are invalid 40 C A Beginner s Guide by Herbert Schildt 10 TA 12 13 14 15 16 as COUNRL De COUNT Ca COUEI d 67 Counc e if How do you create a single line comment How do you create a multiline comment Show the general form of the if statement Show the general form of the for loop How do you create a block of code The moon s gravity is about 17 percent that of Earth s Write a program that displays a table that shows Earth pounds and their equivalent moon weight Have the table run from 1 to 100 pounds Output a newline every 25 pounds A year on Jupiter the time it takes for Jupiter to make one full circuit around the Sun takes a
168. 4 cout lt lt 4 is even n 1f isEven 3 cout lt lt this won t display return 0 Here the function isEven is defined before it is used in main Thus its definition can also serve as its prototype and no separate prototype is needed In general it is usually easier and better to simply declare a prototype for each function used by a program rather than trying to make sure that each function is defined before it is used This is especially true for large programs in which it is hard to keep track of which functions use what other functions Furthermore it is possible to have two functions that call each other In this case prototypes must be used Headers Contain Prototypes Earlier in this book you were introduced to the standard C headers You have learned that these headers contain information needed by your programs While this partial explanation is true it does not tell the whole story C s headers contain the prototypes for the functions in the standard library They also contain various values and definitions used by those functions Like functions that you write the standard library functions must be prototyped before they are used For this reason any program that uses a library function must also include the header containing the prototype of that function To find out which header a library function requires look in your compiler s library documentation Along with a description of each function
169. 4 16 5 25 6 36 7 49 8 64 9 81 10 100 k The advantage to this declaration over the sized version is that the table may be lengthened or shortened without changing the array dimensions CRITICAL SKILL 4 7 Arrays of Strings A special form of a two dimensional array is an array of strings It is not uncommon in programming to use an array of strings The input processor to a database for instance may verify user commands against a string array of valid commands To create an array of strings a two dimensional character array is used with the size of the left index determining the number of strings and the size of the right index specifying the maximum length of each string including the null terminator For example the following declares an array of 30 strings each having a maximum length of 79 characters plus the null terminator char str_array 30 80 Accessing an individual string is quite easy you simply specify only the left index For example the following statement calls gets with the third string in str_array gets str_array 2 To access an individual character within the third string you will use a statement like this cout lt lt str_array 2 3 This displays the fourth character of the third string The following program demonstrates a string array by implementing a very simple computerized telephone directory The two dimensional array numbers holds pairs of names and numbers To find a number you
170. 4 Given ifix lt 10 if y gt 100 1 done x Z else y Z else cout lt lt error what if to what if does the last else associate 5 Show the for statement for a loop that counts from 1000 to O by 2 6 Is the following fragment valid for int i O 1 lt num i sum i count i 7 Explain what break does 8 Inthe following fragment after the break statement executes what is displayed 36 C A Beginner s Guide by Herbert Schildt For i 0 i lt 10 i while running f if x lt y break cout lt lt after while n cout lt lt After forn 9 What does the following fragment print for int 1 0 1 lt 10 i cout lt lt i lt lt 1 1 2 continue cout lt lt n 10 The increment expression in a for loop need not always alter the loop control variable by a fixed amount Instead the loop control variable can change in any arbitrary way Using this concept write a program that uses a for loop to generate and display the progression 1 2 4 8 16 32 and so on 11 The ASCII lowercase letters are separated from the uppercase letters by 32 Thus to convert a lowercase letter to uppercase subtract 32 from it Use this information to write a program that reads characters from the keyboard Have it convert all lowercase letters to uppercase and all uppercase letters to lowercase displaying the result Make no changes to any other character Have
171. 8 Pointers to Derived Types CRITICAL SKILL 10 9 Virtual Functions and Polymorphism CRITICAL SKILL 10 10 Pure Virtual Functions and Abstract Classes This module discusses three features of C that directly relate to object oriented programming inheritance virtual functions and polymorphism Inheritance is the feature that allows one class to inherit the characteristics of another Using inheritance you can create a general class that defines traits common to a set of related items This class can then be inherited by other more specific classes each adding those things that are unique to it Built on the foundation of inheritance is the virtual function The virtual function supports polymorphism the one interface multiple methods philosophy of object oriented programming 1 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 10 1 Inheritance Fundamentals In the language of C a class that is inherited is called a base class The class that does the inheriting is called a derived class Therefore a derived class is a specialized version of a base class A derived class inherits all of the members defined by the base class and adds its own unique elements C implements inheritance by allowing one class to incorporate another class into its declaration This is done by specifying a base class when a derived class is declared Let s begin with a short example that illustrates several of the key features of inheri
172. Add the isMember function shown here which determines if a character is a member of a set Return true if ch is a member of the set Return false otherwise bool Set isMember char ch 1 find ch 1 return true return false This function calls find to determine if ch is a member of the invoking set If it is isMember returns true Otherwise it returns false 6 Begin adding the set operators beginning with set addition To do this overload for objects of type Set as shown here This version adds an element to a set Add a unique element to a set Set Set operator char ch Set newset 1f len MaxSize cout lt lt Set is full n return this return existing set newset this duplicate the existing set see if element already exists 1f find ch 1 if not found then add add new element to new set newset members newset len ch newset len return newset return updated set 47 C A Beginner s Guide by Herbert Schildt This function bears some close examination First a new set is created which will hold the contents of the original set plus the character specified by ch Before the character in ch is added a check is made to see if there is enough room in the set to hold another character If there is room for the new element the original set is assigned to newset Next the find function is called to determine if ch is already part of
173. Herbert Schildt string handling When you use a library function the C compiler automatically links the object code for that function to the object code of your program Because the C standard library is so large it already contains many of the functions that you will need to use in your programs The library functions act as building blocks that you simply assemble You should explore your compiler s library documentation You may be surprised at how varied the library functions are If you write a function that you will use again and again it too can be stored in a library In addition to providing library functions every C compiler also contains a class library which is an object oriented library However you will need to wait until you learn about classes and objects before you can make use of the class library Progress Check 1 What is a function 2 A function is called by using its name True or false 3 What is the C standard function library Answer Key 1 A function is a subroutine that contains one or more C statements 2 True 3 The C standard function library is a collection of functions supplied by all C compilers CRITICAL SKILL 1 11 The C Keywords There are 63 keywords currently defined for Standard C These are shown in Table 1 1 Together with the formal C syntax they form the C programming language Also early versions of C defined the overload keyword but it is obsolet
174. IntRate PayPerYear 1 denom 1 pow b e Payment numer denom Finish the program by outputting the regular payment as shown here cout lt lt Payment is lt lt Payment Here is the entire RegPay cpp program listing Project 2 3 Compute the regular payments for a loan Call this file RegPay cpp ag tinclade lt Lostream gt include lt cmath gt using namespace std int main 4 double Principal original principal double IntRate interest rate such as 0 075 double PayPerYear number of payments per year double NumYears number of years 30 C A Beginner s Guide by Herbert Schildt double Payment the regular payment double numer denom temporary work variables double b e base and exponent for call to pow Cour lt lt Enter principal Gin gt gt Principal cout lt lt Enter interest rate i e 0 075 cin gt gt IntRate cout lt lt Enter number of payments per year cin gt gt PayPerYear cout lt lt Enter number of years Cin gt gt NumYears numer IntRate Principal PayPerYear e PayPerYear NumYears b IntRate PayPerYear 1 denom 1 pow b e Payment numer denom cout lt lt Payment is lt lt Payment return 0 Here is asample run Enter principal 10000 Enter interest rate 1 e 0 07 75 0 075 Enter number of payments per year 12 Enter number of years 5 Payment is 2
175. La El H a a g This val is local to maint int main o int val 10 cout lt lt val in main lt lt val lt lt n Flip cout lt lt val in main lt lt val lt lt n return 0 void 1 int val 88 lAo_o This val is local to fli cout lt lt val in 1 lt lt val lt lt n Here is the output val in main 10 val in f1 88 val in main 10 An integer called val is declared twice once in main and once in f1 The val in main has no bearing on or relationship to the one in f1 The reason for this is that each val is known only to the function in which it is declared As the output shows even though the val declared in f1 is set to 88 the content of val in main remains 10 Because a local variable is created and destroyed with each entry and exit from the block in which it is declared a local variable will not hold its value between activations of its block This is especially important to remember in terms of a function call When a function is called its local variables are created Upon its return they are destroyed This means that local variables cannot retain their values between calls 12 C A Beginner s Guide by Herbert Schildt If a local variable declaration includes an initializer then the variable is initialized each time the block is entered For example A local variable is initialized each
176. Loop Control Variables Inside the for Loop Often the variable that controls a for loop is needed only for the purposes of the loop and is not used elsewhere When this is the case it is possible to declare the variable inside the initialization portion of the for For example the following program computes both the summation and the factorial of the numbers 1 through 5 It declares its loop control variable i inside the for Declare loop control variable inside the for include lt iostream gt using namespace std int main int sum 0 int fact 1 compute the factorial of the numbers through 5 for int i 1 i lt 5 i Here i is declared inside sum i i is known throughout the loop the for loop fact i 18 C A Beginner s Guide by Herbert Schildt but 1 is not known here cout lt lt Sum is lt lt sum lt lt n cout lt lt Factorial is lt lt fact return 0 Here is the output produced by the program Sum is 15 Factorial is 120 When you declare a variable inside a for loop there is one important point to remember the variable is known only within the for statement Thus in the language of programming the scope of the variable is limited to the for loop Outside the for loop the variable will cease to exist Therefore in the preceding example i is not accessible outside the for loop If you need to use the loop control variable elsewhere in your program you
177. O O H D a a E 5 Notice the outer parentheses surrounding the XOR operation inside the cout statements They are necessary because of the precedence of C s operators The lt lt operator is higher in precedence than the logical operators To prove this try removing the outer parentheses and then attempt to compile the program As you will see an error will be reported Progress Check 1 What does the operator do To what types can it be applied 24 C A Beginner s Guide by Herbert Schildt 2 How do you declare an int variable called index with an initial value of 10 3 Of what type is the outcome of a relational or logical expression Answer Key 1 The is the modulus operator which returns the remainder of an integer division It can be applied to integer types 2 int index 10 3 The result of a relational or logical expression is of type bool CRITICAL SKILL 2 6 The Assignment Operator You have been using the assignment operator since Module 1 Now it is time to take a formal look at it The assignment operator is the single equal sign The assignment operator works in C much as it does in any other computer language It has this general form var expression Here the value of the expression is given to var The assignment operator does have one interesting attribute it allows you to create a chain of assignments For example consider this fragment Ii hy Wy Be x y z 100
178. Schildt Each of the other specifiers is examined here auto The auto specifier declares a local variable However it is rarely if ever used because local variables are auto by default It is extremely rare to see this keyword used in a program It is a holdover from the C language CRITICAL SKILL 7 2 extern All the programs that you have worked with so far have been quite small However in reality computer programs tend to be much larger As a program file grows the compilation time eventually becomes long enough to be annoying When this happens you should break your program into two or more separate files Then changes to one file will not require that the entire program be recompiled Instead you can simply recompile the file that changed and link the existing object code for the other files The multiple file approach can yield a substantial time savings with large projects The extern keyword helps support this approach Let s see how In programs that consist of two or more files each file must know the names and types of the global variables used by the program However you cannot simply declare copies of the global variables in each file The reason is that your program can only have one copy of each global variable Therefore if you try to declare the global variables needed by your program in each file an error will occur when the linker tries to link the files It will find the duplicated global variables and will not
179. The do while n n cout lt lt do n cout lt lt statement n cout lt lt while condition n break return Q Ask the Expert Q Can variables be declared inside any other C control statement 26 Earlier you showed how a variable could be declared in the initialization portion of the for loop C A Beginner s Guide by Herbert Schildt A Yes In C it is possible to declare a variable within the conditional expression of an if or switch within the conditional expression of a while loop or within the initialization portion of a for loop A variable declared in one of these places has its scope limited to the block of code controlled by that statement You have already seen an example of declaring a variable within a for loop Here is an example that declares a variable within an if if int x 20 x x y if x gt 10 y 0 The if declares x and assigns it the value 20 Since this is a true value the target of the if executes Because variables declared within a conditional statement have their scope limited to the block of code controlled by that statement x is not known outside the if As mentioned in the discussion of the for loop whether a variable declared within a control statement is known only to that statement or is available after that statement may vary between compilers You should check the compiler that you are using before assuming a specific behavior in this regard Of co
180. This program uses the operator to prevent a division by zero include lt iostream gt using namespace std int div zero 30 C A Beginner s Guide by Herbert Schildt int main int i j result cout lt lt Enter dividend and divisor cin gt gt i gt gt j This statement prevents a divide by zero error result j i j div_zero 7 Use the to prevent a cout lt lt Result lt lt result ad oe divide by zero error return 0 int div_zero cout lt lt Cannot divide by zero n return 0 Here if j is non zero then i is divided by j and the outcome is assigned to result Otherwise the div_zero error handler is called and zero is assigned to result CRITICAL SKILL 7 10 The Comma Operator Another interesting C operator is the comma You have seen some examples of the comma operator in the for loop where it has been used to allow multiple initialization or increment statements However the comma can be used as a part of any expression It strings together several expressions The value of a comma separated list of expressions is the value of the right most expression The values of the other expressions will be discarded This means that the expression on the right side will become the value of the total comma separated expression For example var count 19 incr 10 count 1 first assigns count the value 19 assigns incr the value 10 then adds 1
181. This statement causes a compile time error because there is no automatic conversion from integer to transport You can fix the preceding statement by using a cast as shown here how transport 1 now OK but probably poor style This causes how to contain the value truck because it is the transport constant associated with the value 1 As the comment suggests although this statement is now correct it would be considered to be poor style except in unusual circumstances It is possible to specify the value of one or more of the enumerated constants by using an initializer This is done car 0 by truck 1 airplane 10 train 11 boat 12 following the symbol with an equal sign and an integer value When an initializer is used each symbol that appears after it is assigned a value 1 greater than the previous initialization value For example the following statement assigns the value of 10 to airplane enum transport car truck airplane 10 train boat Now the values of these symbols are as follows 13 C A Beginner s Guide by Herbert Schildt One common but erroneous assumption sometimes made about enumerations is that the symbols can be input and output as a string This is not the case For example the following code fragment will not perform as desired This will not print train on the screen how train cout lt lt how Remember the symbol train is simply a name for an integer
182. ThreeD class Overload the postfix version of ThreeD ThreeD operator int notused Notice the notused parameter ThreeD temp this save original value X increment x y and z tt Z i return temp return original value Notice that this function saves the current state of the operand using the statement ThreeD temp this and then returns temp Keep in mind that the normal meaning of a postfix increment is to first obtain the value of the operand and then to increment the operand Therefore it is necessary to save the current state of the operand and return its original value before it is incremented rather than its modified value The following program implements both forms of the operator 34 C A Beginner s Guide by Herbert Schildt Demonstrate prefix and postfix include lt iostream gt using namespace std class ThreeD int x Y Z 3 D coordinates public ThreeD x y a2z2 0 ThreeD int i int j int k x i y j Z k ThreeD operator prefix version of ThreeD operator int notused postfix version of void show Overload the prefix version of ThreeD ThreeD operator X increment x y and z Yt Z f return this return altered value Overload the postfix version of ThreeD ThreeD operator int notused ThreeD temp this save original va
183. You can still specify a throw clause but such a clause is informational only The following program shows how to specify the types of exceptions that can be thrown from a function Restricting function throw types include lt iostream gt using namespace std This function can only throw ints chars and doubles void Xhandler int test throwfint char double Lo if test 0 throw test throw int Specify the exceptions if test 1 throw a throw char that can be thrown by if test 2 throw 123 23 throw double Xhandler int main cout lt lt start n try Mhandler 0 also try passing 1 and 2 to Xhandler 11 C A Beginner s Guide by Herbert Schildt catch int 1 cout lt lt Caught int n eatech char c f cout lt lt Caught char n catch double d cout lt lt Caught doublen cout lt lt end return OQ In this program the function Xhandler can only throw integer character and double exceptions If it attempts to throw any other type of exception then an abnormal program termination will occur To see an example of this remove int from the list and retry the program An error will result As mentioned currently Visual C does not restrict the exceptions that a function can throw It is important to understand that a function can only be restricted in what types of exceptions it throws back to the try block that has called it
184. _nameN The use of parameter names in a prototype is optional However their use does let the compiler identify any type mismatches by name when an error occurs so it is a good idea to include them To better understand the usefulness of function prototypes consider the following program If you try to compile it an error message will be issued because the program attempts to call sqr_it with an integer argument instead of the integer pointer required There is no automatic conversion from integer to pointer This program uses a function prototype to enforce strong type checking afi void sqr_it int i prototype a Prototype prevents parameter type mismatches Here sqr_it is expecting a pointer but is called with an integer x 10 aqr_it x Error Type mismatch return 0 int x void sqr_it int 1 i j j It is possible for a function definition to also serve as its prototype if the definition occurs prior to the function s first use in the program For example this is a valid program 30 C A Beginner s Guide by Herbert Schildt Use a function s definition as its prototype include lt iostream gt Because isEven is defined before using namespace std it is used its definition also serves as its prototype Determine if a number is even bool isEven int num 1 num 2 return true num is even return false int main if isEven
185. a can be opened in either binary or text mode The only difference is whether character translations take place 71 C A Beginner s Guide by Herbert Schildt The ios trunc value causes the contents of a preexisting file by the same name to be destroyed and the file to be truncated to zero length When creating an output stream using ofstream any preexisting file by that name is automatically truncated The following fragment opens a text file for output ofstream mystream mystream open test Since the mode parameter to open defaults to a value appropriate to the type of stream being opened there is often no need to specify its value in the preceding example Some compilers do not default the mode parameter for fstream open to in out so you might need to specify this explicitly If open fails the stream will evaluate to false when used in a Boolean expression You can make use of this fact to confirm that the open operation succeeded by using a statement like this if Imystream cout lt lt Cannot open file n handle error In general you should always check the result of a call to open before attempting to access the file You can also check to see if you have successfully opened a file by using the is_open function which is a member of fstream ifstream and ofstream It has this prototype bool is open It returns true if the stream is linked to an open file and false otherwise For examp
186. a temporary object Here is an example that illustrates passing an object by reference Constructors destructors and passing objects include lt iostream gt using namespace std class MyClass int val public MyClass int i val i cout lt lt Inside constructor n MyClass cout lt lt Destructing n int getval return val void setval int i val 1 iz void display MyClass amp o0b Here the MyClass object f is passed by reference cout lt lt ob getval lt lt n void change MyClass amp ob ob setval 100 int main MyClass a 10 cout lt lt Before calling display n display a cout lt lt After display returns n change a cout lt lt After calling change n display a return 0 The output is g C A Beginner s Guide by Herbert Schildt Inside constructor Before calling display 10 After display returns After calling change 100 Destructing In this program both display and change use reference parameters Thus the address of the argument not a copy of the argument is passed and the functions operate directly on the argument For example when change is called a is passed by reference Thus changes made to the parameter ob in change affect a in main Also notice that only one call to the constructor and one call to the destructor is made This is because only
187. a consideration in programming the use of pointers to access array elements is very common in C programs Also you can sometimes write tighter code by using pointers instead of array indexing Here is an example that demonstrates the difference between using array indexing and pointer arithmetic to access the elements of an array We will create two versions of a program that reverse the case of letters within a string The first version uses array indexing The second uses pointer arithmetic The first version is shown here Reverse case using array indexing include lt iostream gt include lt cctype gt using namespace std int main int i char str 80 This Is A Test cout lt lt Original string lt lt str lt lt n for i 0 str i i if isupper str i str i tolower str i else if islower str i str i toupper str i cout lt lt Inverted case string lt lt str return O 30 C A Beginner s Guide by Herbert Schildt I The output from the program is shown here Original string This Is A Test Inverted case string tHIS iS a tEST Notice that the program uses the isupper and islower library functions to determine the case of a letter The isupper function returns true when its argument is an uppercase letter islower returns true when its argument is a lowercase letter Inside the for loop str is indexed and the case of each letter is checked and changed
188. a conversion from the type of that argument to the type of the class Remember that the alternative shown here applies only to constructors that have exactly one parameter Progress Check 1 Assuming a class called Test show how to declare a constructor that takes one int parameter called count 2 How can this statement be rewritten Test ob Test 10 3 How else can the declaration in the second question be rewritten CRITICAL SKILL 8 6 Inline Functions Before we continue exploring the class a small but important digression is in order Although it does not pertain specifically to object oriented programming one very useful feature of C called an inline function is frequently used in class definitions An inline function is a function that is expanded inline at the point at which it is invoked instead of actually being called There are two ways to create an inline function The first is to use the inline modifier Ask the Expert Q Can one class be declared within another That is can classes be nested A Yes it is possible to define one class within another Doing so creates a nested class Since a class declaration does in fact define a scope a nested class is valid only within the scope of the enclosing class Frankly because of the richness and flexibility of C s other features such as inheritance discussed later in this book the need to create a nested class is virtually nonexistent For example to
189. a parameter In fact functions that take arguments are called parameterized functions 4 C A Beginner s Guide by Herbert Schildt Progress Check 1 When a function is called what happens to program execution 2 What is the difference between an argument and a parameter 3 Ifa function requires a parameter where is it declared CRITICAL SKILL 5 4 Using return In the preceding examples the function returned to its caller when its closing curly brace was encountered While this is acceptable for many functions it won t work for all Often you will want to control precisely how and when a function returns To do this you will use the return statement The return statement has two forms one that returns a value and one that does not We will begin with the version of return that does not return a value If a function has a void return type that is if the function does not return a value then it can use this form of return return When return is encountered execution returns immediately to the caller Any code remaining in the function is ignored For example consider this program void int main cout lt lt Before callin cout lt lt After call n return 0Q A void function that uses return void f cout lt lt Inside n return return to caller lt This causes an immediate return bypassing the cout lt lt This won t display n remaining cout statement
190. a string void strinvertCase char str while str invert case if isupper str str Colower str else if islower str str toupper str str move on to next char Here is the output tHIS iS a tEST Progress Check 1 Show how to declare a void function called count that has one long int pointer parameter called ptr 2 When a pointer is passed to a function can the function alter the contents of the object pointed to by the pointer 3 Can an array be passed to a function Explain CRITICAL SKILL 5 9 Returning Pointers Functions can return pointers Pointers are returned like any other data type and pose no special problem However because the pointer is one of C s more confusing features a short discussion of pointer return types is warranted To return a pointer a function must declare its return type to be a pointer For example here the return type of f is declared to be an int pointer int f If a function s return type is a pointer then the value used in its return statement must also be a pointer As with all functions the return value must be compatible with the return type The following program demonstrates the use of a pointer return type The function get_substr searches a string for a substring It returns a pointer to the first matching substring If no match is found 24 C A Beginner s Guide by Herbert Schildt a null pointer is returned For
191. a wrong answer too return O The Conditional Expression Sometimes newcomers to C are confused by the fact that any valid C expression can be used to control the if That is the conditional expression need not be restricted to only those involving the relational and logical operators or to operands of type bool All that is required is that the controlling expression evaluate to either a true or false result As you should recall from the previous module a value of 0 is automatically converted into false and all non zero values are converted to true Thus any expression that results in a O or non zero value can be used to control the if For example this program reads two integers from the keyboard and displays the quotient To avoid a divide by zero error an if statement controlled by the second Use an int value to control the if include lt iostream gt using namespace std int main int a b cout lt lt Enter numerator cin gt gt a cout lt lt Enter denominator cin gt gt b 3 C A Beginner s Guide by Herbert Schildt if b cout lt lt Result lt lt a b lt lt n t Notice that b alone is else cout lt lt Cannot divide by zero n sufficient to control this if statement No relational return 0 operator is needed Here are two sample runs Enter numerator 12 Enter denominator 2 Result 6 Enter numerator 12 Enter denominator 0 Cannot divide by zer
192. ace are separate from elements declared in another Namespaces help in the organization of large programs The using statement informs the compiler that you want to use the std namespace This is the namespace in which the entire Standard C library is declared By using the std namespace you simplify access to the standard library Since namespaces are relatively new an older compiler may not support them If you are using an older compiler see Appendix B which describes an easy work around The next line in the program is A C program begins at main This line shows you the second type of comment available in C the single line comment Single line comments begin with and stop at the end of the line Typically C programmers use multiline comments when writing larger more detailed commentaries and single line comments when short remarks are needed This is of course a matter of personal style The next line as the preceding comment indicates is where program execution begins int main All C programs are composed of one or more functions As explained earlier a function is a subroutine Every C function must have a name and the only function that any C program must include is the one shown here called main The main function is where program execution begins and most commonly ends Technically speaking a C program begins with a call to main and in most cases ends when main returns The openi
193. ace std int main int t count for t 0 t10 t count 1 for 7 cout lt lt count lt lt count if count 10 break cout lt lt n return OQ Here is the output produced by this program 23 C A Beginner s Guide by Herbert Schildt 12345 67 8 9 1234567 8 9 1234567 8 9 1234567 8 9 1234567 8 9 12345 67 8 9 L 2345367893 1234567 8 9 12345367 8 9 l2345 67 8 9 As you can see this program prints the numbers 1 through 9 on the screen ten times Each time the break is encountered in the inner for loop control is passed back to the outer for loop Notice that the inner for is an infinite loop that uses the break statement to terminate The break statement can be used with any loop statement It is most appropriate when a special condition can cause immediate termination One common use is to terminate infinite loops as the foregoing example illustrates One other point A break used in a switch statement will affect only that switch and not any loop the switch happens to be in CRITICAL SKILL 3 7 Using continue It is possible to force an early iteration of a loop bypassing the loop s normal control structure This is accomplished using continue The continue statement forces the next iteration of the loop to take place skipping any code between itself and the conditional expression that controls the loop For example the following program prints the even numbers betwee
194. air of operands will be of the same type and the result of each operation will be the same as the type of both operands Converting to and from bool As mentioned earlier values of type bool are automatically converted into the integers O or 1 when used in an integer expression When an integer result is converted to type bool O becomes false and nonzero becomes true Although bool is a fairly recent addition to C the automatic conversions to and from integers mean that it has virtually no impact on older code Furthermore the automatic conversions allow C to maintain its original definition of true and false as zero and nonzero CRITICAL SKILL 2 10 Casts It is possible to force an expression to be of a specific type by using a construct called a cast A cast is an explicit type conversion C defines five types of casts Four allow detailed and sophisticated control over casting and are described later in this book after objects have been explained However there is one type of cast that you can use now It is C s most general cast because it can transform any type into any other type It was also the only type of cast that early versions of C supported The general form of this cast is type expression where type is the target type into which you want to convert the expression For example if you wish to make sure the expression x 2 is evaluated to type float you can write float x 2 Casts are considered operators A
195. alue of a after calling change display a return 0 The output is shown here Value of a before calling change 10 5 C A Beginner s Guide by Herbert Schildt Value of ob inside change 100 Value of a after calling change 10 As the output shows changing the value of ob inside change has no effect on a inside main Constructors Destructors and Passing Objects Although passing simple objects as arguments to functions is a straightforward procedure some rather unexpected events occur that relate to constructors and destructors To understand why consider this short program Constructors destructors and passing objects include lt iostream gt using namespace std class MyClass int val public MyClass int i val i cout lt lt Inside constructor n MyClass cout lt lt Destructing n int getval return val void display MyClass ob cout lt lt ob getval lt lt n int main MyClass a 10 cout lt lt Before calling display n display a cout lt lt After display returns n return OQ This program produces the following unexpected output 6 C A Beginner s Guide by Herbert Schildt Inside constructor Before calling display 10 Destructing Notice the second Destructing message After display returns Destructing As you can see there is one call to the constructor which occurs whe
196. always use the long form of initialization even if the object takes only one argument It s just that the short form is more convenient when only one argument is required The program displays the following output JX OI Uw e L CO OD FW ND 9 10 1i 12 Lo 14 1o 16 CRITICAL SKILL 8 9 Pointers to Objects You can access an object either directly as has been the case in all preceding examples or by using a pointer to that object To access a specific element of an object when using a pointer to the object you must use the arrow operator gt It is formed by using the minus sign followed by a greater than sign 34 C A Beginner s Guide by Herbert Schildt To declare an object pointer you use the same declaration syntax that you would use to declare a pointer for any other type of data The next program creates a simple class called P_example defines an object of that class called ob and defines a pointer to an object of type P_example called p It then illustrates how to access ob directly and how to use a pointer to access it indirectly A simple example using an object pointer include lt iostream gt using namespace std class P_example int num public void set_num int val num val void show _num cout lt lt num lt lt n int main P example ob p declare an object and pointer to it ob set_num 1 call functions directly on ob Pointers to objects are used g
197. ame function names The compiler knows which function belongs to which class because of the scope resolution operator and the class name The body of range consists solely of this line return mpg fuelcap This statement returns the range of the vehicle by multiplying fuelcap by mpg Since each object of type Vehicle has its own copy of fuelcap and mpg when range is called the range computation uses the calling object s copies of those variables Inside range the instance variables fuelcap and mpg are referred to directly without preceding them with an object name or the dot operator When a member function uses an instance variable that is defined by its class it does so directly without explicit reference to an object and without use of the dot operator This is easy to understand if you think about it A member function is always invoked relative to some object of its class Once this invocation has occurred the object is known Thus within a member function there is no need to specify the object a second time This means that fuelcap and mpg inside range implicitly refer to the copies of those variables found in the object that invokes range Of course code outside Vehicle must refer to fuelcap and mpg through an object and by using the dot Operator A member function must be called relative to a specific object There are two ways that this can happen First a member function can be called by code that is outside
198. ames you like However argc and argv have been used by convention for several years and it is best that you use these names so that anyone reading your program can quickly identify them as the command line parameters The argc parameter is an integer that holds the number of arguments on the command line It will always be at least 1 because the name of the program qualifies as the first argument The argv parameter is a pointer to an array of character pointers Each pointer in the argv array points to a string containing a command line argument The program s name is pointed to by argv 0 argv 1 will point to the first argument argv 2 to the second argument and so on All command line arguments are passed to the program as strings so numeric arguments will have to be converted by your program into their proper internal format It is important that you declare argv properly The most common method is 26 C A Beginner s Guide by Herbert Schildt char argv You can access the individual arguments by indexing argv The following program demonstrates how to access the command line arguments It displays all of the command line arguments that are present when it is executed Display command line arguments Introducing Functions Display command line arguments include lt iostream gt using namespace std int main int argc char argv for int 1 0 i lt argc i cout lt lt argv i lt lt n
199. amp a X amp b arguments Here X is the t generic data type X temp temp a a z b b temp int main int i 10 j 20 Float x 10 1 y 23 3 char a x b z cout lt lt Original i j lt lt i lt lt lt lt j lt lt n cout lt lt Original x y lt lt x lt lt e lt y lt lt n cout lt lt Original a b lt lt a lt lt lt lt b lt lt n swapargs i j swap integers The compiler automatically creates versions swapargs x y swap floats of swapargs that use the type of data swapargs a b swap chars specified by its arguments cout lt lt Swapped i j lt lt i lt lt lt lt j lt lt n cout lt lt Swapped x y lt lt x lt lt lt lt y lt lt n cout lt lt Swapped a b e lt a lt lt lt lt b lt lt n return 0 Let s look closely at this program The line template lt class X gt void swapargs X amp a X amp b tells the compiler two things that a template is being created and that a generic definition is beginning Here X is a generic type that is used as a placeholder After the template portion the function swapargs is declared using X as the data type of the values that will be swapped In main the swapargs function is called using three different types of data ints floats and chars Because swapargs is a generic function the compiler auto
200. an enumeration value into a string can be applied to any type of enumeration as long as that enumeration does not contain initializers To properly index the array of strings the enumerated constants must begin at zero and be in strictly ascending order each precisely one greater than the previous Given the fact that enumeration values must be converted manually to their human readable string values they find their greatest use in routines that do not make such conversions It is common to see an enumeration used to define a compiler s symbol table for example 15 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 7 6 typedef C allows you to define new data type names with the typedef keyword When you use typedef you are not actually creating a new data type but rather defining a new name for an existing type This process can help make machine dependent programs more portable only the typedef statements have to be changed It also helps you self document your code by allowing descriptive names for the standard data types The general form of the typedef statement is typedef type name where type is any valid data type and name is the new name for this type The new name you define is in addition to not a replacement for the existing type name For example you could create a new name for float using typedef float balance This statement would tell the compiler to recognize balance as another name for float Next you c
201. ance Progress Check 1 A static local variable its value between function calls 11 C A Beginner s Guide by Herbert Schildt 2 You use extern to declare a variable without defining that variable True or false 3 What specifier requests that the compiler optimize a variable for speed Ask the Expert Q When tried adding the register specifier to a program saw no change in performance Why not A Because of advances in compiler technology most compilers today will automatically optimize your code Thus in many cases adding the register specifier to a declaration might not result in any performance increase because that variable is already optimized However in some cases using register is still beneficial because it lets you tell the compiler which variables you think are the most important to optimize This can be valuable for functions that use a large number of variables all of which cannot be optimized Thus register still fulfills an important role despite advances in compiler design CRITICAL SKILL 7 5 Enumerations In C you can define a list of named integer constants Such a list is called an enumeration These constants can then be used anywhere that an integer can Enumerations are defined using the keyword enum and have this general format enum type name value list variable list Here type name is the type name of the enumeration The value list is a comma separated list of names that represent
202. and S2 are the same then S3 will be the null set The Set class will also include a function called isMember which determines if a specified element is a member of a given set Of course there are several other operations that can be performed on sets Some are developed in the Mastery Check Others you might find fun to try adding on your own For the sake of simplicity the Set class stores sets of characters but the same basic principles could be used to create a Set class capable of storing other types of elements Step by Step 1 Create a new file called Set cpp 2 Begin creating Set by specifying its class declaration as shown here 45 C A Beginner s Guide by Herbert Schildt const int MaxSize 100 class Set int len number of members char members MaxSize this array holds the set The find function is private because it is not used outside the Set class int find char ch find an element public Construct a null set Set len QO Return the number of elements in the set int getLength return len void showset display the set bool isMember char ch check for membership eet operator char ch add an element set operator char ch remove an element Set operator Set ob2 set union Set operator Set ob2 set difference IF Each set is stored in a char array referred to by members The number of members actually in the set is store
203. and be enclosed between parentheses For example this statement accomplishes the same thing as the previous declaration MyClass 0b1 101 This is the most common way that parameterized objects are declared Using this method the general form of passing arguments to a constructor is class type var arg list Here arg list is a comma separated list of arguments that are passed to the constructor 17 C A Beginner s Guide by Herbert Schildt NOTE Technically there is a small difference between the two initialization forms which you will learn about later in this book However this difference does not affect the programs in this module or most programs that you will write Here is a complete program that demonstrates the MyClass parameterized constructor A parameterized constructor include lt iostream gt using namespace std class MyClass public int x Declare constructor and destructor MyClass int i constructor lt Adda parameter MyClass destructor to MyClass Implement a parameterized constructor MyClass MyClass int i x 1 Implement MyClass destructor MyClass MyClass cout lt lt Destructing object whose x value is lt lt w ea n int main MyClass t1 5 Pass arguments to MyClass ta 19 MyClass constructor cout lt lt tl x lt lt lt lt 2 x lt lt n f return 0 The output from this pro
204. and long respectively when the compiler generates the specific instances of myfunc within main Explicitly Overloading a Generic Function Even though a generic function overloads itself as needed you can explicitly overload one too This is formally called explicit specialization If you overload a generic function then that overloaded function overrides or hides the generic function relative to that specific version For example consider the following revised version of the argument swapping example shown earlier 16 C A Beginner s Guide by Herbert Schildt Specializing a template function include lt iostream gt using namespace std template lt class X gt void swapargs X amp a X amp b x temp 17 C A Beginner s Guide by Herbert Schildt temp a a b b temp cout lt lt Inside This overrides void swapargs int int temp temp a a b b temp cout lt lt Inside int main int i 10 j 20 template swapargs n the generic version of swapargs for ints amp a int amp b 7 Explicit overload of swapargs swapargs int specialization n Float x 10 1 y 23 3 char a x b z cout lt lt Original i j lt lt i lt lt g lt j lt lt n cout lt lt Original x y lt lt mx lt lt lt lt y lt lt n cout lt lt Original a b swapargs 1 J swapargs x Yy Swapargs a b
205. and the contents of these can differ between the two objects The following program demonstrates this fact 4 C A Beginner s Guide by Herbert Schildt This program creates two Vehicle objects include lt iostream gt using namespace std Declare the Vehicle class class Vehicle public int passengers number of passengers int fuelcap fuel capacity in gallons int mpg fuel consumption in miles per gallon F int main TEMLEAR minivan create a Vehicle POISE minivan and sportscar Vehicle sportscar create another object each have their own copies of Vehicle s int rangel range2 instance variables Assign values to fields in minivan minivan passengers 7 minivan fuelcap 16 minivan mpg 21 Assign values to fields in sportscar sportscar passengers 2 sportscar fuelcap 14 sportscar mpg 12 Compute the ranges assuming a full tank of gas rangel minivan fuelcap minivan mpg range2z sportscar fuelcap sportscar mpg cout lt lt Minivan can carry lt lt minivan passengers lt lt m m with a range of lt lt rangel lt lt n cout lt lt Sportscar can carry lt lt sportscar passengers lt lt with a range of lt lt range2 lt lt n return 0 The output produced by this program is shown here Minivan can carry 7 with a range of 336 Sportscar can carry 2 with a range of 168 As you Can see minivan s data is complete
206. and the copy of the object used as an argument is destroyed the destructor function is called This is necessary because the object has gone out of scope This is why the preceding program had two calls to the destructor The first was when the parameter to display went out of scope The second is when a inside main was destroyed when the program ended To summarize When a copy of an object is created to be used as an argument to a function the normal constructor is not called Instead the default copy constructor makes a bit by bit identical copy However when the copy is destroyed usually by going out of scope when the function returns the destructor is called Passing Objects by Reference Another way that you can pass an object to a function is by reference In this case a reference to the object is passed and the function operates directly on the object used as an argument Thus changes made to the parameter will affect the argument and passing an object by reference is not applicable to all situations However in the cases in which it is two benefits result First because only an address to the object is being passed rather than the entire object passing an object by reference can be much faster and more efficient than passing an object by value Second when an object is passed by 7 C A Beginner s Guide by Herbert Schildt reference no new object comes into existence so no time is wasted constructing or destructing
207. andj cout lt lt 1 lt lt lt lt j lt lt n min min _swap j 1 cout lt lt Swapped values of 1 andj cout lt lt 1 lt lt lt lt j lt lt n cout lt lt Minimum value is lt lt min lt lt n return O Swap args and return minimum int amp min_swap int amp x int amp y int temp use references to exchange the values of the arguments temp X x Vr y temp return reference to minimum arg 1f x lt y return x else return y 6 A function should not return a reference to a local variable because that variable will go out of scope that is cease to exist when the function returns 7 Overloaded functions must differ in the type and or number of their parameters 15 C A Beginner s Guide by Herbert Schildt j Project 6 1 updated for Mastery Check Create overloaded println functions that display various types of data This version includes an indentation parameter a include lt iostream gt using namespace std These output a newline int ident 0 int ident 0 int ident 0 int ident 0 void println bool b void println int i void printlin long i void println char ch void printlin char str void println double d int ident 0 int ident 0 These functions do not output a newline int ident 0 int ident 0 int ident 0 int ident 0 int ident 0 int ident 0 void pri
208. andled by C cout lt lt strlen Xanadu The answer is that when the compiler encounters a string constant it stores it in the program s string table and generates a pointer to the string Thus Xanadu yields a pointer to its entry in the string table Therefore the following program is perfectly valid and prints the phrase Pointers add power to C include lt iostream gt using namespace std int main char ptr ptr Pointers add power to C n 4 pris assigned the address of this string constant cout lt lt ptr return OQ In this program the characters that make up a string constant are stored in the string table and ptr is assigned a pointer to the string in that table Since a pointer into your program s string table is generated automatically whenever a string constant is used you might be tempted to use this fact to modify the contents of the string table However this is usually not a good idea because many C compilers create optimized tables in which one string constant may be used at two or more different places in your program Thus changing a string may cause undesired side effects ete ed Reversing a String in Place Earlier it was mentioned that comparing one pointer to another is meaningful only if the two pointers point to a common object such as an array Now that you understand how pointers and arrays relate you Can apply pointer comparisons to streamline
209. ange of 420 miles To go 252 miles pickup needs 16 gallons of fuel 5 Many other types of classes can be derived from Vehicle For example the following skeleton creates an off road class that stores the ground clearance of the vehicle Create an off road vehicle class class OffRoad public Vehicle int groundClearance ground clearance in inches public ff The key point is that once you have created a base class that defines the general aspects of an object that base class can be inherited to form specialized classes Each derived class simply adds its own unique attributes This is the essence of inheritance 71 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 10 5 Creating a Multilevel Hierarchy Up to this point we have been using simple class hierarchies consisting of only a base class and a derived class However you can build hierarchies that contain as many layers of inheritance as you like As mentioned it is perfectly acceptable to use a derived class as a base class of another For example given three classes called A B and C C can be derived from B which can be derived from A When this type of situation occurs each derived class inherits all of the traits found in all of its base classes In this case C inherits all aspects of B and A To see how a multilevel hierarchy can be useful consider the following program In it the derived class Triangle is used as a base class to create the derived
210. apacity and its average fuel consumption in miles per gallon 2 C A Beginner s Guide by Herbert Schildt The first version of Vehicle is shown here It defines three instance variables passengers fuelcap and mpg Notice that Vehicle does not contain any functions Thus it is currently a data only class Subsequent sections will add functions to it class Vehicle public int passengers number of passengers int fuelcap fuel capacity in gallons int mpg fuel consumption in miles per gallon The instance variables defined by Vehicle illustrate the way that instance variables are declared in general The general form for declaring an instance variable is shown here type var name Here type specifies the type of variable and var name is the variable s name Thus you declare an instance variable in the same way that you declare other variables For Vehicle the variables are preceded by the public access specifier As explained this allows them to be accessed by code outside of Vehicle A class definition creates a new data type In this case the new data type is called Vehicle You will use this name to declare objects of type Vehicle Remember that a class declaration is only a type description it does not create an actual object Thus the preceding code does not cause any objects of type Vehicle to come into existence To actually create a Vehicle object simply use a declaration statement such as
211. area can be obtained by calling area The interface to this operation is the same no matter what type of shape is being used Progress Check 1 What is a virtual function Why are virtual functions important 3 When an overridden virtual function is called through a base class pointer which version of the function is executed Ag CRITICAL SKILL 10 10 Pure Virtual Functions and Abstract Classes Sometimes you will want to create a base class that defines only a generalized form that will be shared by all of its derived classes leaving it to each derived class to fill in the details Such a class determines the nature of the functions that the derived classes must implement but does not itself provide an implementation of one or more of these functions One way this situation can occur is when a base class is unable to create a meaningful implementation for a function This is the case with the version of TwoDShape used in the preceding example The definition of area is simply a placeholder It will not compute and display the area of any type of object As you will see as you create your own class libraries it is not uncommon for a function to have no meaningful definition in the context of its base class You can handle this situation two ways One way 37 C A Beginner s Guide by Herbert Schildt as shown in the previous example is to simply have it report a warning message While this approach can be useful in certain
212. ared as protected it can be accessed only by members of its class and by its derived classes Thus protected allows a member to be inherited but to remain private within a class hierarchy When a base class is inherited by use of public its public members become public members of the derived class and its protected members become protected members of the derived class When a base class is inherited by use of protected its public and protected members become protected members of 11 C A Beginner s Guide by Herbert Schildt the derived class When a base class is inherited by use of private its public and protected members become private members of the derived class In all cases private members of a base class remain private to that base class Constructors and Inheritance In a hierarchy it is possible for both base classes and derived classes to have their own constructors This raises an important question what constructor is responsible for building an object of the derived class the one in the base class the one in the derived class or both The answer is this the constructor for the base class constructs the base class portion of the object and the constructor for the derived class constructs the derived class part This makes sense because the base class has no knowledge of or access to any element in a derived class Thus their construction must be separate The preceding examples have relied upon the default constructors cr
213. array element include lt iostream gt using namespace std double amp change_it int 1 return a reference double vals 1 1 2 2 32 3 4 4 5 5 int mair int i cout lt lt Here are the original values for i 0 i lt 5 i cout lt lt vals i lt lt cout lt lt n change _it 1 5298 23 change 2nd element change _it 3 98 8 change 4th element cout lt lt Here are the changed values for i 0 i lt 5 i cout lt lt vals i lt lt cout lt lt n return double amp change_it int i return vals i return a reference to the ith element This program changes the values of the second and fourth elements in the vals array The program displays the following output Here are the original values 1 1 2 2 3 3 4 4 5 5 Here are the changed values 1 1 5298 23 3 3 98 8 5 5 Let s see how this is accomplished The change_it function is declared as returning a reference to a double Specifically it returns a reference to the element of vals that is specified by its parameter i The reference returned by change_it is then used in main to assign a value to that element When returning a reference be careful that the object being referred to does not go out of scope For example consider this function 11 C A Beginner s Guide by Herbert Schildt Error cannot return reference to local var int amp f int i 10
214. ase Remember a base class pointer can point to objects of the base class or of any class derived from that base Thus using typeid you can determine at runtime the type of the object that is being pointed to by a base class pointer The following program demonstrates this principle A7 C A Beginner s Guide by Herbert Schildt An example that uses typeid on a polymorphic tinclude lt iostream gt include lt typeinfo gt using namespace std class Base Virtual void fi class Derivedl public Base ii class Derived2 public Base ei li int main Base p Derivedl baseob obl Derived2 ob2 p amp baseob cout lt lt cout lt lt typeid p name p amp obl1 cout lt lt cout lt lt typeid p name p amp ob2 Cout lt lt cout lt lt typeid p name return 0 class hierarch make Base polymorphic o is pointing to an object of type lt lt endl lt lt endl p is pointing to an object of type lt lt endl The output produced by this program is shown here p is pointing to an object of type p is pointing to an object of type p is pointing to an object of type class Base class Derivedl class Derived2 When typeid is applied to a base class pointer of a polymorphic type the type of object pointed to will be determined at runtime as the output shows 48 C A Beginner s Guide by Herbert Schildt
215. assigning many variables the same value using multiple assignments in a single statement For example this fragment assigns count incr and index the value 10 count incr index 10 In professionally written programs you will often see variables assigned a common value using this format 32 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 7 11 Compound Assignment C has a special compound assignment operator that simplifies the coding of a certain type of assignment statement For example x x 10 can be rewritten using a compound assignment operator as shown next x 10 The operator pair tells the compiler to assign to x the value of x plus 10 Compound assignment operators exist for all the binary operators in C that is those that require two operands Their general form is var Op expression Here is another example x x 100 is the same as x 100 Because it saves you some typing compound assignment is also sometimes referred to as shorthand assignment You will see shorthand notation used widely in professionally written C programs so you should become familiar with it CRITICAL SKILL 7 12 Using sizeof Sometimes it is helpful to know the size in bytes of a type of data Since the sizes of C s built in types can differ between computing environments knowing the size of a variable in advance in all situations is not possible To solve this problem C includes the si
216. ated whose only purpose was to output or input the class data While there is nothing in itself wrong with this approach C allows a much better way of performing I O Operations on classes by overloading the lt lt and the gt gt I O operators In the language of C the lt lt operator is referred to as the insertion operator because it inserts data into a stream Likewise the gt gt operator is called the extraction operator because it extracts data from a 4 C A Beginner s Guide by Herbert Schildt stream The operator functions that overload the insertion and extraction operators are generally called inserters and extractors respectively In lt iostream gt the insertion and extraction operators are overloaded for all of the C built in types Here you will see how to define these operators relative to classes that you create Creating Inserters As a simple first example let s create an inserter for the version of the ThreeD class shown here class ThreeD public int x Yy Z 3 D coordinates ThreeD int a int b int c x a y b Z C The C I O System To create an inserter function for an object of type ThreeD overload the lt lt for it Here is one way to do this Display X Y Z coordinates ThreeD inserter ostream amp operator lt lt ostream amp stream ThreeD obj stream lt lt obj x lt lt stream lt lt obj y lt lt stream lt lt obj z lt
217. ation functions A Yes The C standard library contains several other character manipulation functions For example the complement to toupper is tolower which returns the lowercase equivalent of its character argument You can determine the case of a letter by using isupper which returns true if the letter is uppercase and islower which returns true if the letter is lowercase Other character functions include isalpha isdigit isspace and ispunct These functions each take a character argument and 16 C A Beginner s Guide by Herbert Schildt determine the category of that argument For example isalpha returns true if its argument is a letter of the alphabet Progress Check 1 What does the streat function do 2 What does stremp return when it compares two equivalent strings 3 Show how to obtain the length of a string called mystr CRITICAL SKILL 4 6 Array Initialization C allows arrays to be initialized The general form of array initialization is similar to that of other variables as shown here type specifier array_name size value list The value list is a comma separated list of values that are type compatible with the base type of the array The first value will be placed in the first position of the array the second value in the second position and so on Notice that a semicolon follows the In the following example a ten element integer array is initialized wit
218. ation list is shorthand for this longer form MyClass obs 4 MyClass 1 MyClass 2 Another way to MyClass 3 MyClass 4 initialize the array As explained earlier when a constructor takes only one argument there is an implicit conversion from the type of that argument to the type of the class The longer form simply calls the constructor directly When initializing an array of objects whose constructor takes more than one argument you must use the longer form of initialization For example 33 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std class MyClass int x Y public MyClass int i int j x i y j int get_x return x int get_y return y int main MyClass obs 4 2 MyClass 1 2 MyClass 3 4 MyClass 5 6 MyClass 7 8 4 The long initialization MyClass 9 10 MyClass 11 12 form must be used when MyClass 13 14 MyClass 15 16 lwo or more arguments are required by the E object s constructor int i for i 0 i lt 4 i cout lt lt obs i 0 get_x lt lt cout lt lt obs i 0 get_y lt lt n cout lt lt obs i 1 get_x lt lt cout lt lt obs i 1 get_y lt lt n return 0 In this example MyClass constructor takes two arguments In main the array obs is declared and initialized using direct calls to MyClass constructor When initializing arrays you can
219. ations The following program demonstrates this A customized version of strceat include lt iostream gt include lt cstring gt using namespace std void mystrcat char sl char s2 int len 0 Here len defaults to zero int mair char stri 80 This is a test char str2 80 0123456789 mystreat strl str2 5 concatenate 5 chars lt lt lt lt n l i cout strl n j Here len is specified ee and only 5 characters strepy strl this 1s a test reset stril are copied mystreat strl str2 concatenate entire string cout lt lt stri lt lt n Here len defaults to zero and the entire return 0 string is concatenated A custom version of streat void mystrcat char sl char s2 int len Eind end of sl while sl sl14 1 len 0 len strlen s2 while s2 amp amp len s1 s2 copy chars sl si len s1 O null terminate s1 The output from the program is shown here 23 C A Beginner s Guide by Herbert Schildt This is a test01234 this is a test0123456789 As the program illustrates mystrcat concatenates up to len characters from the string pointed to by s2 onto the end of the string pointed to by s1 However if len is zero as it will be when it is allowed to default mystrcat concatenates the entire string pointed to by s2 onto s1 Thus when len is zero the function operates like the standard strca
220. ause a base pointer can always point to a derived object But a dynamic_cast can cast a B pointer into a D pointer only if the object being pointed to actually is a D object In general dynamic_cast will succeed if the pointer or reference being cast is pointing to or referring to either an object of the target type or an object derived from the target type Otherwise the cast will fail If the cast fails then dynamic_cast evaluates to null if the cast involves pointers If a dynamic_cast on reference types fails a bad_cast exception is thrown Here is a simple example Assume that Base is a polymorphic class and that Derived is derived from Base Base bp b_ob Derived dp d_ob bp amp d_ob base pointer points to Derived object dp adynamic_cast lt Derived gt bp cast to derived pointer OF 1f dp cout lt lt Cast OK Here the cast from the base pointer bp to the derived pointer dp works because bp is actually pointing to a Derived object Thus this fragment displays Cast OK But in the next fragment the cast fails because bp is pointing to a Base object and it is illegal to cast a base object into a derived object bp amp b_ob base pointer points to Base object dp dynamic _cast lt Derived gt bp error 1f dp cout lt lt Cast Fails Because the cast fails this fragment displays Cast Fails const_cast The const_cast operator is used to explicitly override const and or volatile in a
221. ause there can only be one endif associated with any if The elif means else if and is used to establish an if else if ladder for multiple compilation options The elif is followed by a constant expression If the expression is true then that block of code is compiled and no other elif expressions are tested or compiled Otherwise the next in the series is checked The general form is if expression statement sequence elif expression statement sequence elif expression 2 statement sequence elif expression 3 statement sequence fi aes elif expression N statement sequence endif For example this fragment uses the value of COMPILED_BY to define who compiled the program define JOHN O0 define BOB 1 define TOM 2 define COMPILED BY JOHN if COMPILED BY JOHN char who Jobn elif COMPILED BY BOB char who Bob else char who Tom endif ifs and elifs can be nested In this case the endif else or elif associate with the nearest if or elif For example the following is perfectly valid 7 C A Beginner s Guide by Herbert Schildt i COMPILED BY BOB if DEBUG FULL int port 198 elif DEBUG PARTIAL int port 200 endif else cout lt lt Bob must compile for debug output n endif H ifdef and ifndef Another method of conditional compilation uses the directives ifdef and ifndef which mean if defined and if not defined respec
222. ax and positive 1f len gt maxOsize len maxQsize else if len lt 0 len 1 size len putloc getloc 0 If the requested queue size is greater than maxQsize then the maximum size queue is created If the requested queue size is zero or less a queue of length 1 is created The size of the queue is stored in the size field The put and get indices are initially set to zero 4 The put function which stores elements is shown next Put a character into the queue void put char ch 1f putloc size cout lt lt Queue is full n return putloc gq putlec ch The function begins by checking for a queue full condition If putloc is equal to the size of the queue then there is no more room in which to store elements Otherwise putloc is incremented and the new element is stored at that location Thus putloc is always the index of the last element stored 5 To retrieve elements use the get function shown next Get a character from the queues char get 1f getloc putloc cout lt lt Queue is empty n return 0 getloc return q qgetloc 28 C A Beginner s Guide by Herbert Schildt Notice first the check for queue empty If getloc and putloc both index the same element then the queue is assumed to be empty This is why getloc and putloc were both initialized to zero by the Queue constructor Next getloc is incremented and the next element is
223. be empty but this is seldom the case in practice Progress Check 1 What is the main difference between the while and the do while loops 2 Can the body of a while loop be empty Ask the Expert Q Given the flexibility inherent in all of C s loops what criteria should use when selecting a loop That is how do choose the right loop for a specific job A Use a for loop when performing a known number of iterations Use the do while when you need a loop that will always perform at least one iteration The while is best used when the loop will repeat an unknown number of times The while checks its condition at the top of the loop The do while checks its condition at the bottom of the loop Thus a do while will always execute at least once Yes the body of a while loop or any other C loop can be empty Improve the C Help System This project expands on the C help system that was created in Project 3 1 Thisversion adds the syntax for the for while and do while loops It also checks the user s menu selection looping until a valid response is entered To do this it uses a do while loop In general using a do while loop to handle menu selection is common because you will always want the loop to execute at least once Step by Step 1 Copy Help cpp to a new file called Help2 cpp 23 C A Beginner s Guide by Herbert Schildt 2 Change the portion of the program that displays the choices so that it
224. binary data to or from a file First you can write a byte using the member function put and read a byte using the member function get The second way uses the block I O functions read and write Each is examined here Using get and put The get function has many forms but the most commonly used version is shown next along with that of put istream amp get char amp ch ostream amp put char ch The get function reads a single character from the associated stream and puts that value in ch It returns a reference to the stream This value will be null if the end of the file is reached The put function writes ch to the stream and returns a reference to the stream The following program will display the contents of any file on the screen It uses the get function 25 C A Beginner s Guide by Herbert Schildt Display a file using get tinclude lt iostream gt include lt fstream gt using namespace std int main int argc char argv char ch if arge 2 cout lt lt Usage PR lt filename gt n return 1 Open the file for binary operations ifstream in argv 1 ios in oss binary _l if in cout lt lt Cannot open fFile n return 1 Read data until the end of the file is reached while in in will be false when eof is neachea _ in get ch if in cout lt lt ch in close return 0 Look closely at the while
225. ble to control when the increment or decrement operation takes place The precedence of the arithmetic operators is shown here Highest unary minus R Lowest Operators on the same precedence level are evaluated by the compiler from left to right Of course parentheses may be used to alter the order of evaluation Parentheses are treated by C in the same way that they are by virtually all other computer languages they force an operation or a set of operations to have a higher precedence level 19 C A Beginner s Guide by Herbert Schildt Ask the Expert Q Does the increment operator have anything to do with the name C A Yes As you know C is built upon the C language C adds to C several enhancements most of which support object oriented programming Thus C represents an incremental improvement to C and the addition of the which is of course the increment operator to the name C is a fitting way to describe C Stroustrup initially named C C with Classes but at the suggestion of Rick Mascitti he later changed the name to C While the new language was already destined for success the adoption of the name C virtually guaranteed its place in history because it was a name that every C programmer would instantly recognize CRITICAL SKILL 2 5 Relational and Logical Operators In the terms relational operator and logical operator relational refers to the relationships that va
226. blic void set_x int i x i int get_x return x int main MyClass obs 4 Create an array of objects int i for i 0 i lt 4 i obs i set_x i for i 0 1 lt 4 i cout lt lt obs lt lt i lt lt get_x obs i get_x lt lt n return OQ This program produces the following output obs 0 lt geu x U Obs Li lt Get x 1 ObslZ lt G6l x 2 Obs 3 egt x 3 CRITICAL SKILL 8 8 Initializing Object Arrays If a class includes a parameterized constructor an array of objects can be initialized For example here MyClass is a parameterized class and obs is an initialized array of objects of that class Initialize an array of objects include lt iostream gt using namespace std class MyClass int x public MyClass int i x i int get_x return x 32 C A Beginner s Guide by Herbert Schildt int main MyClass obs 4 l 2 3 4 One way to initialize int i an array of objects for i 0 i lt 4 i cout lt lt obs lt lt 1 lt lt get_x lt lt obs i get_x lt lt n return In this example the values 1 through 4 are passed to the MyClass constructor function This program displays the following output Obs Olegi xt Obs 1 l lt GEe 20 s 2 Obs lZi lt Geu_x 2 3 obs 3 get x 4 Actually the syntax shown in the initializ
227. bout 12 Earth years Write a program that converts Jovian years to Earth years Have the user specify the number of Jovian years Allow fractional years When a function is called what happens to program control Write a program that averages the absolute value of five values entered by the user Display the result 41 C A Beginner s Guide by Herbert Schildt Module 2 Introducing Data Types and Operators Table of Contents CRITICAL SKILL 2 1 The C Data Types Project 2 1 Talking to Mars CRITICAL SKILL 2 2 Literals CRITICAL SKILL 2 3 A Closer Look at Variables CRITICAL SKILL 2 4 Arithmetic Operators CRITICAL SKILL 2 5 Relational and Logical Operators Project 2 2 Construct an XOR Logical Operation CRITICAL SKILL 2 6 The Assignment Operator CRITICAL SKILL 2 7 Compound Assignments CRITICAL SKILL 2 8 Type Conversion in Assignments CRITICAL SKILL 2 9 Type Conversion in Expressions CRITICAL SKILL 2 10 Casts CRITICAL SKILL 2 11 Spacing and Parentheses Project 2 3 Compute the Regular Payments on a Loan At the core of a programming language are its data types and operators These elements define the limits of a language and determine the kind of tasks to which it can be applied As you might expect C supports a rich assortment of both data types and operators making it suitable for a wide range of programming Data types and operators are a large subject We will begin here with an examination of C s foundati
228. break case 5 cout lt lt The do while n n cout lt lt do n cout lt lt statement n cout lt lt while condition n break case 6 cout lt lt The break n n cout lt lt break n break case 7 cout lt lt The continue n n cout lt lt continue n break case S8 cout lt lt The goto n n cout lt lt goto label n break cout lt lt n Show the help menu void Help showmenu C A Beginner s Guide by Herbert Schildt cout lt lt Help on n cout lt lt 1 if n cout lt lt 2 switch n cout lt lt 3 Eor n cout lt lt 4 while n cout lt lt 5 do while n cout lt lt 6 break n cout lt lt 7 continue n cout lt lt 8 goto n cout lt lt Choose one q to quit Return true if a selection is valid bool Help isvalid char ch if ch lt 1 ch gt 8 amp amp ch q return false else return true int main char choice Help hlpob 27 create an instance of the Help class cout lt lt User ID is lt lt hlpob getID lt lt n Use the Help object to display information Fore 4 do hlpob showmenu cin gt gt choice while hlpob isvalid choice if choice q break cout lt lt n hlpob helpon choice return O 28 C A Beginner s Guide by Herbert Schildt Module 9 A Closer Look at Class
229. but before it has been assigned it will contain an arbitrary value Should you try to use the pointer prior to giving it a value you will probably crash your program While there is no sure way to avoid using an uninitialized pointer C programmers have adopted a procedure that helps prevent some errors By convention if a pointer contains the null zero value it is assumed to point to nothing Thus if all unused pointers are given the null value and you avoid the use of a null pointer you can avoid the accidental misuse of an uninitialized pointer This is a good practice to follow 39 C A Beginner s Guide by Herbert Schildt Any type of pointer can be initialized to null when it is declared For example the following initializes p to null float p 0 p is now a null pointer To check for a null pointer use an if statement like one of these if p succeeds if p is not null if p succeeds if p is null Progress Check 1 String constants used in a program are stored ina 2 What does this declaration create float fpa 18 3 By convention a pointer containing null is assumed to be unused True or false CRITICAL SKILL 4 12 Multiple Indirection A pointer to a pointer is a form of multiple indirection or a chain of pointers Consider Figure 4 2 As you can see in the case of a normal pointer the value of the pointer is the address of a value In the case of a pointer to a pointer the first pointer contains th
230. c throw MyExcpt Here is one way to add an exception to Queue It is one of many solutions Add an exception to Project 12 1 A template queue class include lt iostream gt include lt cstring gt using namespace std This is the exception thrown by Queue on error class QOExcpt public char msg 80 const int maxOsize 100 This creates a generic queue class template lt class OType gt class Queue OType q maxQsize this array holds the queue int size maximum number of elements that the queue can store int putloc getloc the put and get indices OExcpt Qerr add an exception field public Construct a queue of a specific length Queue int len Queue must be less than max and positive if len gt maxQsize len maxQsize else if len lt 0 len 1 size len putloc getloc 0 35 C A Beginner s Guide by Herbert Schildt 36 Put data into the queue void put QOType data 1f putloc size strepy Qerr msg Queue is full n throw Oerr putloc q putloc data Get data from the queue OType get 1f getloc putloc strepy Qerr msg Queue is empty n throw Oerr getloct return g getloc 1 Demonstrate the generic Queue int main notice that 10a is only 2 elements long Queue lt int gt 10a 2 10b 10 try 1Q0a put 1 1Q0a put 2 iQ0a put 3 this will overflow 10b put
231. c principles before you write even a simple C program Object oriented programming took the best ideas of structured programming and combined them with several new concepts The result was a different and better way of organizing a program In the most general sense a program can be organized in one of two ways around its code what is happening or around its data who is being affected Using only structured programming techniques programs are typically organized around code This approach can be thought of as code acting on data Object oriented programs work the other way around They are organized around data with the key principle being data controlling access to code In an object oriented language you define the data and the routines that are permitted to act on that data Thus a data type defines precisely what sort of operations can be applied to that data To support the principles of object oriented programming all OOP languages including C have three traits in common encapsulation polymorphism and inheritance Let s examine each Encapsulation Encapsulation is a programming mechanism that binds together code and the data it manipulates and that keeps both safe from outside interference and misuse In an object oriented language code and data can be bound together in such a way that a self contained black box is created Within the box are all necessary data and code When code and data are linked togethe
232. cannot begin with a digit or be the same as a C keyword 10 A single line comment begins with and ends at the end of the line A multiline comment begins with and ends with 11 The general form of the if if condition statement The general form of the for for initialization condition increment statement 12 A block of code is started with a and ended with a 13 Show a table of Earth to Moon weights include lt iostream gt using namespace std int main 1 C A Beginner s Guide by Herbert Schildt double earthweight weight on earth double moonweight weight on moon int counter counter 0 for earthweight 1 0 earthweight lt 100 0 earthweight moonweight earthweight 0 17 cout lt lt earthweight lt lt earth pounds is equivalent to lt lt moonweight lt lt moon pounds n counter 1i counter 25 cout lt lt n counter 0 return 0 14 Convert Jovian years to Earth years include lt iostream gt using namespace std int main double e years earth years double j_years Jovian years cout lt lt Enter number of Jovian years cin gt gt j_years e years j_years 12 0 cout lt lt Equivalent Earth years lt lt e years return 0 15 When a function is called program control transfers to that function 16 Average the absolute values of 5 numbers 2 C A Beginner s Guide by He
233. cast The target type must be the same as the source type except for the alteration of its const or volatile attributes The most common use of const_cast is to remove const ness The general form of const_cast is shown here const_cast lt type gt expr 50 C A Beginner s Guide by Herbert Schildt Here type specifies the target type of the cast and expr is the expression being cast into the new type It must be stressed that the use of const_cast to cast away const ness is a potentially dangerous feature Use it with care One other point Only const_cast can cast away const ness That is dynamic_cast static_cast and reinterpret_cast cannot alter the const ness of an object Static_cast The static_cast operator performs a non polymorphic cast It can be used for any standard conversion No runtime checks are performed Thus the static_cast operator is essentially a substitute for the original cast operator Its general form is static_cast lt type gt expr Here type specifies the target type of the cast and expr is the expression being cast into the new type reinterpret_cast The reinterpret_cast operator converts one type into a fundamentally different type For example it can change a pointer into an integer and an integer into a pointer It can also be used for casting inherently incompatible pointer types Its general form is reinterpret_cast lt type gt expr Here type specifies the target type of the cast an
234. cation for one purpose or another is an important part of nearly all real world programs Memory to satisfy a dynamic allocation request is taken from the heap As you might guess it is possible under fairly extreme cases for free memory to become exhausted Therefore while dynamic allocation offers greater flexibility it too is finite High memory Stack Global data Program code Low memory Figure 12 1 A conceptual view of memory usage in a C program C provides two dynamic allocation operators new and delete The new operator allocates memory and returns a pointer to the start of it The delete operator frees memory previously allocated using new The general forms of new and delete are shown here p var new type delete p_var Here p_var is a pointer variable that receives a pointer to memory that is large enough to hold an item of type type Since the heap is finite it can become exhausted If there is insufficient available memory to fill an allocation request then new will fail and a bad_alloc exception will be generated This exception is 27 C A Beginner s Guide by Herbert Schildt defined in the header lt new gt Your program should handle this exception and take appropriate action if a failure occurs If this exception is not handled by your program then your program will be terminated The actions of new on failure as just described are specified by Standard C The trouble is that some older comp
235. ccess to the private members of MyClass Specifically it can access x a and x b Notice also that comDenom is called normally that is not in conjunction with an object and the dot operator Since it is nota member function it does not need to be qualified with an object s name In fact it cannot be qualified with an object Typically a friend function is passed one or more objects of the class for which it is a friend as is the case with comDenom While there is nothing gained by making comDenom a friend rather than a member function of MyClass there are some circumstances in which friend functions are quite valuable First friends can be useful for overloading certain types of operators as described later in this module Second friend functions simplify the creation of some types of I O functions as described in Module 11 The third reason that friend functions may be desirable is that in some cases two or more classes can contain members that are interrelated relative to other parts of your program For example imagine 17 C A Beginner s Guide by Herbert Schildt two different classes called Cube and Cylinder that define the characteristics of a cube and cylinder of which one of these characteristics is the color of the object To enable the color of a cube and cylinder to be easily compared you can define a friend function that compares the color component of each object returning true if the colors match and false
236. ch as stacks and queues A stack is a list in which elements can be accessed in first in last out FILO order only A queue is a list in which elements can be accessed in first in first out FIFO order only Thus a stack is like a stack of plates on a table the first down is the last to be used A queue is like a line at a bank the first in line is the first served What makes data structures such as stacks and queues interesting is that they combine storage for information with the functions that access that information Thus stacks and queues are data engines in which storage and retrieval is provided by the data structure itself and not manually by your program Such a combination is obviously an excellent choice for a class and in this project you will create a simple queue class In general queues support two basic operations put and get Each put operation places a new element on the end of the queue Each get operation retrieves the next element from the front of the queue Queue operations are consumptive Once an element has been retrieved it cannot be retrieved again The queue can also become full if there is no space available to store an item and it can become empty if all of the elements have been removed One last point there are two basic types of queues circular and non circular A circular queue reuses locations in the underlying array when elements are removed A non circular queue does not and eventually becomes exhaus
237. constructor that is automatically invoked when a copy of an object is required To begin let s review why you might need to explicitly define a copy constructor By default when an object is passed to a function a bitwise that is exact copy of that object is made and given to the function parameter that receives the object However there are cases in which this identical copy is not desirable For example if the object uses a resource such as an open file then the copy will use the Same resource as does the original object Therefore if the copy makes a change to that resource it will be changed for the original object too Furthermore when the function terminates the copy will be destroyed thus causing its destructor to be called This may cause the release of a resource that is still needed by the original object A similar situation occurs when an object is returned by a function The compiler will generate a temporary object that holds a copy of the value returned by the function This is done automatically and is beyond your control This temporary object goes out of scope once the value is returned to the calling routine causing the temporary object s destructor to be called However if the destructor destroys something needed by the calling code trouble will follow At the core of these problems is the creation of a bitwise copy of the object To prevent them you need to define precisely what occurs when a copy of an obj
238. coordinates void ThreeD show cout lt lt x lt lt cout lt lt y lt lt cout lt lt z lt lt n int main ThreeD a 1 2 3 m cout lt lt Original value of a a show a f increment a cout lt lt Value after a e a show return 0 The output is shown here Original value of a 1 2 3 Value after ta 2 3 4 33 C A Beginner s Guide by Herbert Schildt As the output verifies operator increments each coordinate in the object and returns the modified object Again this is in keeping with the traditional meaning of the operator As you know the and have both a prefix and a postfix form For example both x and A Closer Look at Classes X are valid uses of the increment operator As the comments in the preceding program state the operator function defines the prefix form of relative to the ThreeD class However it is possible to overload the postfix form as well The prototype for the postfix form of the operator relative to the ThreeD class is shown here ThreeD operator int notused The parameter notused is not used by the function and should be ignored This parameter is simply a way for the compiler to distinguish between the prefix and postfix forms of the increment operator The postfix decrement uses the same approach Here is one way to implement a postfix version of relative to the
239. copy constructor let s look at another related situation that can also benefit from a copy constructor CRITICAL SKILL 9 4 Returning Objects Just as objects can be passed to functions functions can return objects To return an object first declare the function as returning a class type Second return an object of that type using the normal return statement The following program has a member function called mkBigger It returns an object that gives val a value twice as large as the invoking object 9 C A Beginner s Guide by Herbert Schildt Returning objects include lt iostream gt using namespace std class MyClass int val 10 C A Beginner s Guide by Herbert Schildt public Normal constructor MyClass int i val i cout lt lt Inside constructor n MyClass cout lt lt Destructing n int getval return val Return an object MyClass mkBigger mkBigger returns a MyClass object MyClass o val 2 return o i void display MyClass ob cout lt lt ob getval lt lt n int main cout lt lt Before constructing a n MyClass a 10 cout lt lt After constructing a n n cout lt lt Before call to display n display la cout lt lt After display returns n n cout lt lt Before call to mkBigger n a a mkBigger cout lt lt After mkBigger returns n n cout lt lt Befo
240. countered The array pointed to by buf will be null terminated by get If the delimiter character is encountered in the input stream it is not extracted Instead it remains in the stream until the next input operation The third overloaded form of get returns the next character from the stream It returns EOF a value that indicates end of file if the end of the file is encountered EOF is defined by lt iostream gt One good use for get is to read a string that contains spaces As you know when you use gt gt to read a string it stops reading when the first whitespace character is encountered This makes gt gt useless for reading a string containing spaces However you can overcome this problem by using get buf num as illustrated in this program 29 C A Beginner s Guide by Herbert Schildt Use get to read a string that contains spaces include lt iostream gt include lt fstream gt using namespace std int main char str 80 cout lt lt Enter your name i cin get str 79 4 Use get to read a string that contains whitespace cout lt lt str lt lt n return 0 Here the delimiter to get is allowed to default to a newline This makes get act much like the standard gets function getline Another function that performs input is getline It isa member of each input stream class Its prototypes are shown here istream amp getline char buf strea
241. cout lt lt n cout lt lt Info for tz n t2 showstyle t2 showDim cout lt lt Area is lt lt t2 area lt lt n return 0 Here Triangle calls TwoDShape with the parameters w and h which initializes width and height using these values Triangle no longer initializes these values itself It need only initialize the value unique to it style This leaves TwoDShape free to construct its subobject in any manner that it so chooses Furthermore TwoDShape can add functionality about which existing derived classes have no knowledge thus preventing existing code from breaking Any form of constructor defined by the base class can be called by the derived class constructor The constructor executed will be the one that matches the arguments For example here are expanded versions of both TwoDShape and Triangle that include additional constructors Add a constructor to TwoDbDShape include lt iostream gt include lt cstring gt using namespace std A class for two dimensional objects class TwoDShape these are private double width double height public 16 C A Beginner s Guide by Herbert Schildt Default constructor TwobsShape width height 0 0 Constructor for TwoDsShape TwobShape double w double h width w height h Construct object with equal width and height TwobDshape double x width height x void showDim cout lt lt
242. cout setf ios showpos cout setf los scientific cout lt lt 123 lt lt lt lt 1233 23 lt lt n F Set the precision cout precision 2 two digits after decimal inea cout width 10 in a field of 10 characters cout lt lt 123 lt lt T cout width 10 set width to 10 Set field width cout lt lt 123 23 lt lt n cout fill1 fill using lt Set the fill character cout width 10 in a field of 10 characters cout lt lt 123 lt lt cout width 10 set width to 10 cout lt lt 123 23 return OC The program displays this output 4123 41 2332300e4 002 123 41 24304 002 HHHRHHY123 1 23e 002 As mentioned in some implementations it is necessary to reset the field width before each output operation This is why width is called repeatedly in the preceding program There are overloaded forms of width precision and fill that obtain but do not change the current setting These forms are shown here char fill streamsize width streamsize precision Progress Check 1 What does boolalpha do 2 What does setf do 3 What function is used to set the fill character 15 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 10 5 Using I O Manipulators The C I O system includes a second way in which you can alter the format parameters of a stream This method uses special functions called manipulators tha
243. create an inline function called f that returns an int and takes no parameters you declare it like this inline int f a The inline modifier precedes all other aspects of a function s declaration 22 C A Beginner s Guide by Herbert Schildt The reason for inline functions is efficiency Every time a function is called a series of instructions must be executed both to set up the function call including pushing any arguments onto the stack and to return from the function In some cases many CPU cycles are used to perform these procedures However when a function is expanded inline no such overhead exists and the overall speed of your program will increase Even so in cases where the inline function is large the overall size of your program will also increase For this reason the best inline functions are those that are small Most large functions should be left as normal functions The following program demonstrates inline Demonstrate inline include lt iostream gt using namespace std class cl int i private by default public int get_i void put_i int j 3 inline int cl get_i return i get_i and put_if are expanded inline inline void cl put_ifint j _ S put_i 10Q cout lt lt s get_i return It is important to understand that technically inline is a request not a command that the compiler generate inline code There are various situations
244. create another object int rangel range2 Assign values to fields in minivan Minivan passengers 7 minivan fuelcap 16 minivan mpg 21 Assign values to fields in sportscar sportscar passengers 2 sportscar fuelcap 14 sportscar mpg 12 g C A Beginner s Guide by Herbert Schildt Compute the ranges assuming a full tank of gas rangel minivan range Call rangel on Vehicle objects rangez sportscar range cout lt lt Minivan can carry lt lt Mminivan passengers lt lt with a range of lt lt rangel lt lt n cout lt lt Sportscar can carry lt lt sportscar passengers lt lt with a range of lt lt range2 lt lt n return 0 This program displays the following output Minivan can carry 7 with a range of 336 Sportscar can carry 2 with a range of 168 Progress Check 1 What is the operator called 2 What does do 3 Ifa member function is called from outside its class it must be called through an object using the dot operator True or false Project 8 1 Creating a Help Class If one were to try to summarize the essence of the class in one sentence it might be this A class encapsulates functionality Of course sometimes the trick is knowing where one functionality ends and another begins As a general rule you will want your classes to be the building blocks of your larger application To do this each class must represent a
245. creates a generic queue class template lt class OType gt class Queue OType gq maxQOsize this array holds the queue int size maximum number of elements that the queue can store int putloc getloc the put and get indices public Construct a queue of a specific length Queue int len Queue must be less than max and positive 1f len gt maxQOsize len maxQOsize else if len lt 0 len 1 size len putloc getloc 0 39 C A Beginner s Guide by Herbert Schildt Put data into the queue void put OType data 1f putloc size cout lt lt Queue is full n return putloc qlputloc data Get data from the queue OType get t 1f getloc putloc cout lt lt Queue is empty n return OQ getloct return q getloc Demonstrate the generic Queue int main Queue lt Sample gt sampQO 3 Sample ol 1 o2 2 o3 3 sampQ put ol samp put o2 sampQ put 03 cout lt lt Contents of sampQ n for int i 0 1 lt 3 itt sampQO get show cout lt lt endl return 0 8 Here the Sample objects are allocated 40 C A Beginner s Guide by Herbert Schildt 41 Use Project 12 1 to store Sample objects Allocate the Sample objects dynamically A template queue class ai include lt iostream gt using namespace std class Sample int id public Sample id 0 Sample int x i
246. creating too many specializations then you are probably better off not using a template class in the first place Progress Check 1 What keyword is used to declare a generic function or class 2 Cana generic function be explicitly overloaded 3 Ina generic class are all of its member functions also automatically generic ORIA Creating a Generic Queue Class In Project 8 2 you created a Queue class that maintained a queue of characters In this project you will convert Queue into a generic class that can operate on any type of data Queue is a good choice for conversion to a generic class because its logic is separate from the data upon which it functions The same mechanism that stores integers for example can also store floating point values or even objects of classes that you create Once you have defined a generic Queue class you can use it whenever you need a queue Step by Step 1 Begin by copying the Queue class from Project 8 2 into a file called GenericQ cpp 2 Change the Queue declaration into a template as shown here template lt class QType gt class Queue Here the generic data type is called QType 3 Change the data type of the q array to QType as shown next 23 C A Beginner s Guide by Herbert Schildt QType q maxQsize this array holds the queue Because q is now generic it can be used to hold whatever type of data an object of Queue declares 4 Change the data type of the parameter to the put
247. ct If not why not int f int x 10 double b CRITICAL SKILL 6 9 Function Overloading and Ambiguity Before concluding this module it is necessary to discuss a type of error unique to C ambiguity It is possible to create a situation in which the compiler is unable to choose between two or more correctly overloaded functions When this happens the situation is said to be ambiguous Ambiguous statements are errors and programs containing ambiguity will not compile By far the main cause of ambiguity involves C s automatic type conversions C automatically attempts to convert the type of the arguments used to call a function into the type of the parameters defined by the function Here is an example 29 C A Beginner s Guide by Herbert Schildt int myfunc double d fi cout lt lt myfunc c not an error conversion applied As the comment indicates this is not an error because C automatically converts the character c into its double equivalent Actually in C very few type conversions of this sort are disallowed While automatic type conversions are convenient they are also a prime cause of ambiguity Consider the following program Overloading ambiguity include lt iostream gt using namespace std Float myfunc float i double myfunc double 1 int main unambiguous calls myfunc double cout lt lt myfunc 10 1 lt lt ambiguous cout lt lt myfunc 10 Er
248. cts are pointed to through a base class pointer different versions of the virtual 28 C A Beginner s Guide by Herbert Schildt function are executed The same effect occurs when a virtual function is called through a base class reference You declare a virtual function as virtual inside a base class by preceding its declaration with the keyword virtual When a virtual function is redefined by a derived class the keyword virtual need not be repeated although it is not an error to do so A class that includes a virtual function is called a polymorphic class This term also applies to a class that inherits a base class containing a virtual function The following program demonstrates a virtual function 29 C A Beginner s Guide by Herbert Schildt A short example that uses a virtual function include lt iostream gt using namespace std class B Declare a virtual function public Virtual void who specify a virtual function cout lt lt Base n F class D1 public B public void who redefine who for Dl Redefine the virtual function for D1 cout lt lt First derivation n t3 class D2 public B public void who redefine who for D2 Redefine the virtual function a cout lt lt Second derivation n second time for D2 F int mairi E base_obj E p D1 Dl_obj D2 D2 obj p amp base_obj p who access E s who p amp
249. d int main f int x 19 x is known to all code 1f x 19 int y 20 y is local to the if block cout lt lt xX y is lt lt x y lt lt n y 100 Error y not known here return OQ The variable x is declared at the start of main s scope and is accessible to all subsequent code within main Within the if block y is declared Since a block defines a scope y is visible only to other code within its block This is why outside of its block the line y 100 is commented out If you remove the leading comment symbol a compile time error will occur because y is not visible outside of its block Within the if block x can be used because code within a block has access to variables declared by an enclosing block Although local variables are typically declared at the beginning of their block they need not be A local variable can be declared anywhere within a block as long as it is declared before it is used For example this is a perfectly valid program 14 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std int main cout lt lt Enter a number int a declare one variable cin gt gt a cout lt lt Enter a second number int b declare another variable cin gt gt b cout lt lt Product return g lt a b lt lt n Here a and bare declared as needed
250. d amp str len 1 Notice that end points to the last character in the string not the null terminator 4 Add the code that reverses the string 35 C A Beginner s Guide by Herbert Schildt while start lt end swap chars t start start end end t advance pointers start end The process works like this As long as the start pointer points to a memory location that is less than the end pointer the loop iterates Inside the loop the characters being pointed to by start and end are swapped Then start is incremented and end is decremented When end is greater than or equal to start all of the characters in the string have been reversed Since both start and end point into the same array their comparison is meaningful 5 Here is the complete StrRev cpp program 36 C A Beginner s Guide by Herbert Schildt i Project 4 32 Reverse a string in place include lt iostream gt include lt cstring gt using namespace std int main char str this is a test char start end int len char t cout lt lt Original lt lt str lt lt n len strlen str start str end amp str len 1 while start lt end swap chars t start start end and t advance pointers atart 4 end cout lt lt Reversed lt lt str lt lt n return OQ The output from the program is shown here Original this is a test Rev
251. d float fp In this case the base type of fp is float which means that it can be used to point to a float value 23 C A Beginner s Guide by Herbert Schildt In general in a declaration statement preceding a variable name with an causes that variable to become a pointer CRITICAL SKILL 4 9 The Pointer Operators There are two special operators that are used with pointers and amp The amp is a unary operator that returns the memory address of its operand Recall that a unary operator requires only one operand For example ptr amp total puts into ptr the memory address of the variable total This address is the location of total in the computer s internal memory It has nothing to do with the value of total The operation of amp can be remembered as returning the address of the variable it precedes Therefore the preceding assignment statement could be verbalized as ptr receives the address of total To better understand this assignment assume that the variable total is located at address 100 Then after the assignment takes place ptr has the value 100 The second operator is and it is the complement of amp It is a unary operator that returns the value of the variable located at the address specified by its operand Continuing with the same example if ptr contains the memory address of the variable total then val ptr will place the value of total into val For example if
252. d x void show cout lt lt id lt lt endl hi const int maxOsize 100 This creates a generic queue class template lt class OType gt class Queue OType q maxQOsize this array holds the queue int size maximum number of elements that the queue can store int putloc getloc the put and get indices public Construct a queue of a specific length Queue int len Queue must be less than max and positive 1f len gt maxOsize len maxQsize else if len lt 0 len 1 size len putloc getloc 0 C A Beginner s Guide by Herbert Schildt 42 Put data into the queue void put Type data 1f putloc size cout lt lt Queue is full n return putloc q putloc data Get data from the queue OType get 1f getloc putloc cout lt lt Queue is empty n return 0 getloct return gq getloc Demonstrate the generic Queue int main i Queue lt Sample gt samp 3 Sample pl p2 p3 pl new Sample l1 p2 new Sample 2 p3 new Sample 3 sampQ put p1 sampQ put p2 sampQ put p3 cout lt lt Contents of sampQ n for int 1 0 i lt 3 i t sampO get show cout lt lt endl delete p1 delete p2 delete p3 return 0 C A Beginner s Guide by Herbert Schildt 9 To declare a namespace called RobotMotion use namespace RobotMotion
253. d To create a forward declaration to a class simply use the form shown in this program A friend of one class can be a member of another For example here is the preceding program rewritten so that sameColor is a member of Cube Notice the use of the scope resolution operator when declaring sameColor to be a friend of Cylinder 19 C A Beginner s Guide by Herbert Schildt A function can be a member of one class and a friend of another include lt iostream gt using namespace std class Cylinder a forward declaration enum colors red green yellow class Cube colors color public Cube colors c color c bool sameColor Cylinder y q _ _ sameColor is now ff tax a member of Cube class Cylinder colors color public Cylinder colors c color c friend bool Cube sameColor Cylinder y Cube sameColor is If sae a friend of Cylinder bool Cube sameColor Cylinder y i1f color y color return true else return false int main Cube cubel red Cube cube green Cylinder cyl green 1f cubel sameColor cyl cout lt lt cubel and cyl are the same color n else cout lt lt cubel and cyl are different colors n i cube2 sameColor cyl cout lt lt cubes and cyl are the same color n else cout lt lt cube2 and cyl are different colors n return 0 20 C A Beginner s Guide by Herbert Schildt S
254. d a string call gets with the name of the array without any index as its argument Upon return from gets the array will hold the string input from the keyboard The gets function will continue to read characters including whitespace until you enter a carriage return The header used by gets is lt cstdio gt This version of the preceding program uses gets to allow the entry of strings containing spaces 12 C A Beginner s Guide by Herbert Schildt Using gets to read a string from the keyboard include lt iostream gt include lt cstdio gt using namespace std int mair char str 80 i Read a string using gets cout lt lt Enter a string gets str read a string using gets P cout lt lt Here is your string cout lt lt str return OQ Here is asample run Enter a string This is a test Here is your string This is a test Now spaces are read and included in the string One other point Notice that in a cout statement str can be used directly In general the name of a character array that holds a string can be used any place that a string constant can be used Keep in mind that neither cin nor gets performs any bounds checking on the array that receives input Therefore if the user enters a string longer than the size of the array the array will be overwritten Later you will learn an alternative to gets that avoids this problem Progress Check
255. d expr is the expression being cast into the new type What Next The purpose of this book is to teach the core elements of the language These are the features and techniques of C that are used in everyday programming With the knowledge you now have you can begin writing real world professional quality programs However C is a very rich language and it contains many advanced features that you will still want to master including e The Standard Template Library STL e Explicit constructors e Conversion functions e const member functions and the mutable keyword e The asm keyword e Overloading the array indexing operator the function call operator and the dynamic allocation operators new and delete Of the preceding perhaps the most important is the Standard Template Library It is a library of template classes that provide off the shelf solutions to a variety of common data storage tasks For 51 C A Beginner s Guide by Herbert Schildt example the STL defines generic data structures such as queues stacks and lists which you can use in your programs You will also want to study the C function library It contains a wide array of routines that will simplify the creation of your programs To continue your study of C suggest reading my book C The Complete Reference published by Osborne McGraw Hill Berkeley California It covers all of the preceding and much much more You now have sufficient kno
256. d for its most common usage Thus when the default arguments apply you need to remember and specify only the arguments that are meaningful to the exact situation not all those needed for the most general case Default Arguments Versus Overloading One application of default arguments is as a shorthand form of function overloading To see why this is the case imagine that you want to create two customized versions of the standard strcat function One version will operate like strcat and concatenate the entire contents of one string to the end of another The other version will take a third argument that specifies the number of characters to concatenate That is this second version will concatenate only a specified number of characters from one string to the end of another Thus assuming that you call your customized functions mystrcat they will have the following prototypes void mystrcat char s1 char s2 int len void mystrcat char s1 char s2 27 C A Beginner s Guide by Herbert Schildt The first version will copy len characters from s2 to the end of s1 The second version will copy the entire string pointed to by s2 onto the end of the string pointed to by s1 and will operate like strcat While it would not be wrong to implement two versions of mystrcat to create the two versions that you desire there is an easier way Using a default argument you can create only one version of mystrcat that performs both oper
257. d in len The maximum size of a set is MaxSize which is set to 100 You can increase this value if you work with larger sets The Set constructor creates a null set which is a set with no members There is no need to create any other constructors or to define an explicit copy constructor for the Set class because the default bitwise copy is sufficient The getLength function returns the value of len which is the number of elements currently in the set 3 Begin defining the member functions starting with the private function find as shown here Return the index of the element specified by ch or 1 if not found int Set find char ch int i for i 0 1 lt len i if members i ch return i return l1 This function determines if the element passed in ch is a member of the set It returns the index of the element if it is found and 1 if the element is not part of the set This function is private because it is not 46 C A Beginner s Guide by Herbert Schildt used outside the Set class As explained earlier in this book member functions can be private to their class A private member function can be called only by other member functions in the class 4 Add the showset function as shown here Show the set void Set showset cout lt lt for int i 0 i lt lenm i cout lt lt members i lt lt cout lt lt n This function displays the contents of a set 5
258. d on 8 or 16 instead of 10 The number system based on 8 is called octal and it uses the digits O through 7 In octal the number 10 is the same as 8 in decimal The base 16 number system is called hexadecimal and uses the digits O through 9 plus the letters A through F which stand for 10 11 12 13 14 and 15 For example the hexadecimal number 10 is 16 in decimal Because of the frequency with which these two number systems are used C allows you to specify integer literals in hexadecimal or octal instead of decimal A hexadecimal literal must begin with Ox a zero followed by an x An octal literal begins with a zero Here are some examples hex OxFF 255 in decimal oct 011 9 in decimal String Literals C supports one other type of literal in addition to those of the predefined data types the string A string is a set of characters enclosed by double quotes For example this is a test is a string You have seen examples of strings in some of the cout statements in the preceding sample programs Keep in mind one important fact although C allows you to define string constants it does not have a built in string data type Instead as you will see a little later in this book strings are supported in C as character arrays C does however provide a string type in its class library Ask the Expert Q You showed how to specify a char literal Is a wchar_t literal specified in the same way A No A wide characte
259. de by Herbert Schildt Even in this case however Quicksort still performs correctly The version of Quicksort that we will develop selects the middle element of the array as the comparand One other thing The C library contains a function called qsort which also performs a Quicksort You might find it interesting to compare it to the version shown here Step By Step 1 Create a file called QSDemo cpp 2 The Quicksort will be implemented by a pair of functions The first called quicksort provides a convenient interface for the user and sets up a call to the actual sorting function called qs First create the quicksort function as shown here Set up a call to the actual sorting function void quicksort char items int len qs items 0 len 1 Here items points to the array to be sorted and len specifies the number of elements in the array As shown in the next step qs requires an initial partition which quicksort supplies The advantage of using quicksort is that it can be called with just a pointer to the array to be sorted and the number of elements in the array It then provides the beginning and ending indices of the region to be sorted 3 Add the actual Quicksort function called qs shown here A recursive version of Quicksort for sorting characters void qs char items int left int right int i j char xX Y i left j right x items left right 2 do
260. default Since the class keyword is expressly designed to support encapsulation it makes sense that its members are private by default Thus to avoid incompatibility with C on this issue the structure default could not be altered so a new keyword was added However in the long term there is a more important reason for the separation of structures and classes Because class is an entity syntactically separate from struct the definition of a class is free to evolve in ways that may not be syntactically compatible with C like structures Since the two are separated the future direction of C will not be encumbered by concerns of compatibility with C like structures For the most part C programmers will use a class to define the form of an object that contains member functions and will use a struct in its more traditional role to create objects that contain only data members Sometimes the acronym POD is used to describe a structure that does not contain member functions It stands for plain old data Unions A union is a memory location that is shared by two or more different variables A union is created using the keyword union and its declaration is similar to that of a structure as shown in this example union utype short int i char ch P This defines a union in which a short int value and a char value share the same location Be clear on one point It is not possible to have this union hold both an integer and a charact
261. derived class any initialization it needs to perform is separate from and possibly prerequisite to any initialization performed by the derived class Therefore the base class constructor must be executed first Likewise it is quite sensible that destructors be executed in reverse order of derivation Since the base class underlies a derived class the destruction of the base class implies the destruction of the derived class Therefore the derived destructor must be called before the object is fully destroyed CRITICAL SKILL 10 8 Pointers to Derived Types Before moving on to virtual functions and polymorphism it is necessary to discuss an important aspect of pointers Pointers to base classes and derived classes are related in ways that other types of pointers are not In general a pointer of one type cannot point to an object of another type However base class pointers and derived objects are the exceptions to this rule In C a base class pointer can also be used to point to an object of any class derived from that base For example assume that you have a base class called B and a class called D which is derived from B Any pointer declared as a pointer to B can also be used to point to an object of type D Therefore given B p pointer to object of type B E B_ob object of type B D D_ob object of type D both of the following statements are perfectly valid amp B ob p points to object of type E amp D_ob p p
262. dress of D2_ obj the version of who declared inside D2 is executed To review When a virtual function is called through a base class pointer the version of the virtual function actually executed is determined at runtime by the type of object being pointed to Although virtual functions are normally called through base class pointers a virtual function can also be called normally using the standard dot operator syntax This means that in the preceding example it would have been syntactically correct to access who using this statement D1_obj who However calling a virtual function in this manner ignores its polymorphic attributes It is only when a virtual function is accessed through a base class pointer or reference that runtime polymorphism is achieved At first the redefinition of a virtual function in a derived class seems to be a special form of function overloading However this is not the case In fact the two processes are fundamentally different First an overloaded function must differ in its type and or number of parameters while a redefined virtual function must have exactly the same type and number of parameters In fact the prototypes for a virtual function and its redefinitions must be exactly the same If the prototypes differ then the function is Simply considered to be overloaded and its virtual nature is lost Another restriction is that a virtual function must be a member not a friend of the class for w
263. e 19 A C A Beginner s Guide by Herbert Schildt Maximum value 100 Notice how the program cycles through the elements in the nums array Storing the values in an array makes this process easy As the program illustrates the loop control variable of a for loop is used as an index Loops such as this are very common when working with arrays There is an array restriction that you must be aware of In C you cannot assign one array to another For example the following is illegal int a 10 b 10 IE srs a b error illegal To transfer the contents of one array into another you must assign each value individually like this for i 0 i lt 10 i a i b i No Bounds Checking C performs no bounds checking on arrays This means that there is nothing that stops you from overrunning the end of an array In other words you can index an array of size N beyond N without generating any compile time or runtime error messages even though doing so will often cause catastrophic program failure For example the compiler will compile and run the following code without issuing any error messages even though the array crash is being overrun int crash 10 i for i 0 i lt 100 i crash i i In this case the loop will iterate 100 times even though crash is only ten elements long This causes memory that is not part of crash to be overwritten Ask the Expert Q Since overrunning an array can lead to catastrophic
264. e Keep in mind that C is a case sensitive language and it requires that all keywords be in lowercase 38 C A Beginner s Guide by Herbert Schildt asm auto bool break const continue default delete dynamic_cast a static_cast template ao i volatile wehar_t while Table 1 1 The C Keywords CRITICAL SKILL 1 12 Identifiers In C an identifier is a name assigned to a function variable or any other user defined item Identifiers can be from one to several characters long Variable names can start with any letter of the alphabet or an underscore Next comes a letter a digit or an underscore The underscore can be used to enhance the readability of a variable name as in line_count Uppercase and lowercase are seen as different that is to C myvar and MyVar are separate names There is one important identifier restriction you cannot use any of the C keywords as identifier names In addition predefined identifiers such as cout are also off limits Here are some examples of valid identifiers Test x y2 Maxlner up _top my_var simplelnterest23 Remember you cannot start an identifier with a digit Thus 980K is invalid Good programming practice dictates that you use identifier names that reflect the meaning or usage of the items being named 39 C A Beginner s Guide by Herbert Schildt Progress Check 1 Which is the keyword for For or FOR 2 A C identifier can contain what type of characters
265. e and a local variable have the same name all references to that variable name inside the function in which the local variable is declared will refer to the local variable and have no effect on the global variable Thus a local variable hides a global variable of the same name Global variables are initialized at program startup If a global variable declaration includes an initializer then the variable is initialized to that value If a global variable does not include an initializer then its value is set to zero Storage for global variables is in a fixed region of memory set aside for this purpose by your program Global variables are helpful when the same data is used by several functions in your program or when a variable must hold its value throughout the duration of the program You should avoid using unnecessary global variables however for three reasons They take up memory the entire time your program is executing not just when they are needed Using a global variable where a local variable will do makes a function less general because it relies on something that must be defined outside itself Using a large number of global variables can lead to program errors because of unknown and unwanted side effects A major problem in developing large programs is the accidental modification of a variable s value due to its use elsewhere in a program This can happen in C if you use too many global variables in your programs Progre
266. e here is how to overload the minus for the ThreeD class Overload subtraction ThreeD ThreeD operator ThreeD op2 ThreeD temp temp x X op2a x temp y Y op2 y temp Z Z op2 zZ return temp Remember it is the operand on the left that invokes the operator function The operand on the right is passed explicitly Using Member Functions to Overload Unary Operators You can also overload unary operators such as or the unary or As stated earlier when a unary operator is overloaded by means of a member function no object is explicitly passed to the operator function Instead the operation is performed on the object that generates the call to the function through the implicitly passed this pointer For example here is a program that defines the increment operation for objects of type ThreeD 32 C A Beginner s Guide by Herbert Schildt Overload the unary operator include lt iostream gt using namespace std class ThreeD int x Yy Z 3 D coordinates public ThreeD x y zZ OQ ThreeD int i int j int k x i y Jj Z k ThreeD operator prefix version of void show Overload the prefix version of ThreeD ThreeD operator Overload for ThreeD X increment x y and z yet Zt f return this lt Retum the incremented object Show X Y Z
267. e lt iostream gt using namespace std A try catch is reset each time a function is enter void Xhandler int test try a This try block is local to Xhandler 1f test throw test catch int i cout lt lt Caught One Ex lt lt i lt lt n int main cout lt lt start n Ahandler 1 Ahandler 2 0 3 handler handler f cout lt lt end return Q This program displays the following output start 6 C A Beginner s Guide by Herbert Schildt Caught One Ex 1 Caught One Ex 2 Caught One Ex 3 end In this example three exceptions are thrown After each exception the function returns When the function is called again the exception handling is reset In general a try block is reset each time it is entered Thus a try block that is part of a loop will be reset each time the loop repeats Progress Check 1 Inthe language of C what is an exception 2 Exception handling is based on what three keywords 3 An exception is caught based on its type True or false Using Multiple catch Statements As stated earlier you can associate more than one catch statement with a try In fact it is common to do so However each catch must catch a different type of exception For example the program shown next catches both integers and character pointers Use multiple catch statements include lt iostream gt using namespace std
268. e r cin gt gt n cout lt lt Enter divisor y Pihis if cin gt gt d 1e target of this I i is the entire bleck the target of this if is a block if d 0 cout lt lt d does not equal zero so division is OF lt lt n result n d 5 il F ul cout lt lt n lt lt F lt lt d g 4s gg result return OU Here is asample run Enter value 10 Enter divisor 2 d does not equal zero so division is OK 10 2 is 5 In this case the target of the if statement is a block of code and not just a single statement If the condition controlling the if is true as it is in the sample run the three statements inside the block will be executed Try entering a zero for the divisor and observe the result In this case the code inside the block is bypassed As you will see later in this book blocks of code have additional properties and uses However the main reason for their existence is to create logically inseparable units of code Ask the Expert Q Does the use of a code block introduce any runtime inefficiencies In other words do the and consume any extra time during the execution of my program 31 C A Beginner s Guide by Herbert Schildt A No Code blocks do not add any overhead whatsoever In fact because of their ability to simplify the coding of certain algorithms their use generally increases speed and efficiency Semicolons and Positioning In C the semicol
269. e the address of a global variable might be passed to an interrupt driven clock routine that updates the variable with each tick of the clock In this situation the contents of the variable are altered without the use of any explicit assignment statement in the program The reason the external alteration of a variable may be important is that a C compiler is permitted to automatically optimize certain expressions on the assumption that the content of a variable is unchanged if it does not occur on the left side of an assignment statement However if factors beyond program control change the value of a variable then problems can occur To prevent such problems you must declare such variables volatile as shown here volatile int current_users Because it is declared as volatile the value of current_users will be obtained each time it is referenced Progress Check 1 Can the value of a const variable be changed by the program 2 Ifa variable has its value changed by events outside the program how should that variable be declared Storage Class Specifiers There are five storage class specifiers supported by C They are auto extern register Static mutable These are used to tell the compiler how a variable should be stored The storage specifier precedes the rest of the variable declaration The mutable specifier applies only to class objects which are discussed later in this book 4 C A Beginner s Guide by Herbert
270. e ways to declare a parameter that is to receive an array pointer First it can be declared as an array of the same type and size as that used to call the function as shown here 20 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std void display int num 10 int main int t 10 i for i 0 i lt 10 i t 1i 1 display t pass array t to a function return OQ Print some numbers void display int num 10 Parameter declared f as a sized array int i for i 0 i lt 10 i cout lt lt num i lt lt Even though the parameter num is declared to be an integer array of ten elements the C compiler will automatically convert it to an int pointer This is necessary because no parameter can actually receive an entire array Since only a pointer to the array will be passed a pointer parameter must be there to receive it A second way to declare an array parameter is to specify it as an unsized array as shown here void display int num Parameter declared as an unsized array int i for i 0 i lt 10 i cout lt lt num i lt lt Here num is declared to be an integer array of unknown size Since C provides no array boundary checks the actual size of the array is irrelevant to the parameter but not to the program of course This method of declaration is also automatically transformed into an int pointer by the compiler
271. e 223 used in the AND statement is the decimal representation of 1101 1111 Thus the AND operation leaves all bits in ch unchanged except for the sixth one which is set to zero The AND operator is also useful when you want to determine whether a bit is on or off For example this statement checks to see if bit 4 in status is set if status amp 8 cout lt lt bit 4 is on The reason 8 is used is that in binary it is represented as 0000 1000 That is the number 8 translated into binary has only the fourth bit set Therefore the if statement can succeed only when bit 4 of status is also on An interesting use of this feature is the show_binary function shown next It displays in binary format the bit pattern of its argument You will use show_binary later in this module to examine the effects of other bitwise operations 18 C A Beginner s Guide by Herbert Schildt Display the bits within a byte void show_binary unsigned int u int t for t 128 t gt 0 t t 2 1f u amp t cout lt lt 1 else cout lt lt O Te i cout lt lt wn The show_binary function works by successively testing each bit in the low order byte of u using the bitwise AND to determine if it is on or off If the bit is on the digit 1 is displayed otherwise O is displayed The bitwise OR as the reverse of AND can be used to turn bits on Any bit that is set to 1 in either operand will cause the corresponding bit i
272. e address of the second pointer which points to the location that contains the desired value Multiple indirection can be carried on to whatever extent desired but there are few cases where more than a pointer to a pointer is needed or indeed even wise to use Excessive indirection is difficult to follow and prone to conceptual errors Pointer Variable Single Indirection Pointer Pointer Variable a Multiple indirection Figure 4 2 Single and multiple indirection 40 C A Beginner s Guide by Herbert Schildt A variable that is a pointer to a pointer must be declared as such This is done by placing an additional asterisk in front of its name For example this declaration tells the compiler that balance is a pointer to a pointer of type int int balance It is important to understand that balance is not a pointer to an integer but rather a pointer to an int pointer When a target value is indirectly pointed to by a pointer to a pointer accessing that value requires that the asterisk operator be applied twice as is shown in this short example include lt iostream gt using namespace std int main int x p q x 10 p amp x Assign p the address of x q amp p Assign q the address of p cout lt lt q prints the value of x 4 Access x s value through q return 0 Notice that two are required Ask the Expert Q Given the power of pointers can see that their m
273. e been placed anywhere as long as it was not in a function Remember though that since you must declare a variable before you use it it is best to declare global variables at the top of the program 16 C A Beginner s Guide by Herbert Schildt Use a global variable tinclude lt iostream gt using namespace std void funcl void func om is global int count This is a global variable int main int i This is a local variable for i 0 i lt 10 i count i 2 lt This refers to the global count func return 0 This also refers to the global count void funcl cout lt lt count lt lt count access global count cout lt lt n output a newline Func void func This count is local to func2 int count this is a local variable for count 0 count lt 3 count4 cout lt lt This refers to the local count The output from the program is shown here count U COUN Z Ccount 4 counts 6 COUNT Count 10 sCOuUme 17 scount 14 count 16 Count e LB 17 C A Beginner s Guide by Herbert Schildt Looking closely at this program it should be clear that both main and func1 use the global variable count In func2 however a local variable called count is declared When func2 uses count it is referring to its local variable not the global one It is important to understand that if a global variabl
274. e contains the keyword auto which can be used to declare local variables However since all local variables are by default assumed to be auto it is virtually never used Thus you will not see it used in any of the examples in this book However if you choose to use it place it immediately before the variable s type as shown here auto char ch Again auto is optional and not used elsewhere in this book CRITICAL SKILL 5 7 Global Scope Since local variables are known only within the function in which they are declared a question may have occurred to you How do you create a variable that can be shared by more than one function The answer is to declare the variable in the global scope The global scope is the declarative region that is outside of all functions Declaring a variable in the global scope creates a global variable Global variables are known throughout the entire program They can be used by any piece of code and they maintain their values during the entire execution of the program Therefore their scope extends to the entire program You can create global variables by declaring them outside of any function Because they are global they can be accessed by any expression regardless of which function contains the expression The following program demonstrates the use of a global variable The variable count has been declared outside of all functions Its declaration is before the main function However it could hav
275. e created you can change the type of data operated upon by MyClass A template class can have more than one generic data type Simply declare all the data types required by the class in a comma separated list within the template specification For instance the following example creates a class that uses two generic data types This example uses two generic data types in a class definition include lt iostream gt using namespace std template lt class Tl class T2 gt class MyClass Tl i T2 J public MyClass T1 a T2 b 1 a j b void show cout lt lt ji ze lt lt J lt lt n int main MyClass lt int double gt ob1 10 0 23 MyClass lt char char gt ob2 X This is a test obl show show int double ob2 show show char char return OQ This program produces the following output 71 C A Beginner s Guide by Herbert Schildt TO 023 X This is a test The program declares two types of objects ob1 uses int and double data ob2 uses a character and a character pointer For both cases the compiler automatically generates the appropriate data and functions to accommodate the way the objects are created Explicit Class Specializations As with template functions you can create a specialization of a generic class To do so use the template lt gt construct as you did when creating explicit function specializations For example Demonstrate
276. e main function code which would in effect cause the entire program to be monitored When an exception is thrown it is caught by its corresponding catch statement which then processes the exception There can be more than one catch statement associated with a try The type of the exception determines which catch statement is used That is if the data type specified by a catch statement matches that of the exception then that catch statement is executed and all others are bypassed When an exception is caught arg will receive its value Any type of data can be caught including classes that you create 2 C A Beginner s Guide by Herbert Schildt The general form of the throw statement is shown here throw exception throw generates the exception specified by exception If this exception is to be caught Exceptions Templates and Other Advanced Topics then throw must be executed either from within a try block itself or from any function called from within the try block directly or indirectly If an exception is thrown for which there is no applicable catch statement an abnormal program termination will occur That is your program will stop abruptly in an uncontrolled manner Thus you will want to catch all exceptions that will be thrown Here is a simple example that shows how C exception handling operates A simple exception handling example include lt iostream gt using namespace std int main c
277. e referenced as if they had been declared as normal local variables In fact relative to your program that is exactly how you will use them Further even though they are defined within a union declaration they are at the same scope level as any other local variable within the same block This implies that the names of the members of an anonymous union must not conflict with other identifiers known within the same scope All restrictions involving unions apply to anonymous ones with these additions First the only elements contained within an anonymous union must be data No member functions are allowed Anonymous unions cannot contain private or protected elements The protected specifier is discussed in Module 10 Finally global anonymous unions must be specified as static CRITICAL SKILL 9 8 The this Keyword Before moving on to operator overloading it is necessary to describe another C keyword this Each time a member function is invoked it is automatically passed a pointer called this to the object on which it is called The this pointer is an implicit parameter to all member functions Therefore inside a member function this can be used to refer to the invoking object As you know a member function can directly access the private data of its class For example given this class 26 C A Beginner s Guide by Herbert Schildt class Test f int i void if inside f the following statement can be
278. e right rotate is slightly more complicated than the left rotate because the value passed in val must be shifted into the second byte of t so that bits being shifted off the right side can be caught Once the rotation is complete the value must be shifted back into the low order byte of t so that the value can be returned Because the bit being shifted out moves to bit 7 the following statement checks whether that value is a 1 26 C A Beginner s Guide by Herbert Schildt if t amp 128 The decimal value 128 has only bit 7 set If it is set then t is ORed with 32768 which is the decimal value in which bit 15 is set and bits 14 through O are cleared This causes bit 15 of t to be set and the other bits to remain unchanged 4 Here is an entire program that demonstrates lrotate and rrotate It uses the show_binary function to display the results of each rotation Project 7 1 Left and right rotate functions for byte values a include lt iostream gt using namespace std unsigned char rrotate unsigned char val int n unsigned char lrotate unsigned char val int n void show_binary unsigned int u int maini char ch T cout lt lt Original value in binary n show_binary ch cout lt lt Rotating right 8 times n for int i 0 i lt B i ch rrotate ch 1 show_binary ch 27 C A Beginner s Guide by Herbert Schildt cout lt lt Rotating left 8 times n for int
279. e source file into object code The __TIME__ macro contains the time at which the program was compiled The time is represented in a string having the form hour minute second The meaning of __STDC__ is implementation defined Generally if STDC __ is defined then the compiler will accept only standard C C code that does not contain any nonstandard extensions A compiler conforming to ANSI ISO Standard C will define _ cplusplus as a value containing at least six digits Nonconforming compilers will use a value with five or fewer digits 11 C A Beginner s Guide by Herbert Schildt
280. e that depends upon the size of the C data types Remember since the sizes of types in C are defined by the implementation it is bad style to make assumptions about their sizes in code that you write Progress Check 1 Show how to assign the variables t1 t2 and t3 the value 10 using one assignment statement 2 Howcan x x 100 be rewritten 3 The sizeof operator returns the size of a variable or type in More Data Types and Operators Precedence Summary Table 7 2 lists the precedence from highest to lowest of all C operators Most operators associate from left to right The unary operators the assignment operators and the operator associate from right to left Note that the table includes a few operators that you have not yet learned about many of which are used in object oriented programming 34 C A Beginner s Guide by Herbert Schildt Precedence Operators Highest gt l amp sizeof new delete typeid type casts oe gt 1 lt lt gt gt lt lt gt gt gt gt lt lt amp Lowest Table 7 2 Precedence of the C Operators Module 7 Mastery Check 1 Show how to declare an int variable called test that can t be changed by the program Give it an initial value of 100 2 The volatile specifier tells the compiler that a variable might be changed by forces outside the
281. e your own C programs be prepared to encounter ambiguity errors Unfortunately until you become more experienced you will find that they are fairly easy to create Module 6 Mastery Check What are the two ways that an argument can be passed to a subroutine In C what is a reference How is a reference parameter created Given this fragment int f char amp c int i H xe char ch x int i 10 show how to call f with the ch and i 4 Create a void function called round that rounds the value of its double argument to the nearest whole value Have round use a reference parameter and return the rounded result in this parameter You can assume that all values to be rounded are positive Demonstrate round ina program To solve this problem you will need to use the modf standard library function which is shown here double modf double num double i 32 C A Beginner s Guide by Herbert Schildt The modf function decomposes num into its integer and fractional parts It returns the fractional portion and places the integer part in the variable pointed to by i It requires the header lt cmath gt 5 Modify the reference version of swap so that in addition to exchanging the values of its arguments it returns a reference to the smaller of its two arguments Call this function min_swap Why can t a function return a reference to a local variable How must the parameter lists of two overloaded functions diffe
282. ea int range Assign values to fields in minivan minivan passengers 7 minivan fuelcap 16 4 Notice the use of the dot mMinivan mpg 21 operator to access a member Compute the range assuming a full tank of gas range minivan fuelcap minivan mpg cout lt lt Minivan can carry lt lt Minivan passengers lt lt with a range of lt lt range lt lt n return 0 Let s look closely at this program The main function creates an instance of Vehicle called minivan Then the code within main accesses the instance variables associated with minivan assigning them values and then using those values The code inside main can access the members of Vehicle because they are declared public If they had not been specified as public their access would have been limited to the Vehicle class and main would not have been able to use them When you run the program you will see the following output Minivan can carry 7 with a range of 336 Before moving on let s review a fundamental principle each object has its own copies of the instance variables defined by its class Thus the contents of the variables in one object can differ from the contents of the variables in another There is no connection between the two objects except for the fact that they are both objects of the same type For example if you have two Vehicle objects each has its own copy of passengers fuelcap and mpg
283. eated automatically by C so this was not an issue However in practice most classes will define constructors Here you will see how to handle this situation When only the derived class defines a constructor the process is straightforward simply construct the derived class object The base class portion of the object is constructed automatically using its default constructor For example here is a reworked version of Triangle that defines a constructor It also makes style private since it is now set by the constructor 12 C A Beginner s Guide by Herbert Schildt Add a constructor to Triangle include lt iostream gt include lt cstring gt using namespace std A class for two dimensional objects class TwoDShape these are private double width double height public void showDim cout lt lt Width and height are lt lt width lt lt and lt lt height lt lt accessor functions double getWidth return width double getHeight return height void setWidth double w width w void setHeight double h height h t Triangle is derived from TwoDShape class Triangle public TwoDShape char style 20 now private public Constructor for Triangle Triangle char str double w double h Initialize the base class portion An ee pk H Initialize the TwoDShape setnelg h portion of Triangle Initialize the derived class portion
284. ect is made so that you can avoid undesired side effects The way you accomplish this is by creating a copy constructor Before we explore the use of the copy constructor it is important for you to understand that C defines two distinct types of situations in which the value of one object is given to another The first situation is assignment The second situation is initialization which can occur three ways When one object explicitly initializes another such as in a declaration When a copy of an object is made to be passed to a function When a temporary object is generated most commonly as a return value 13 C A Beginner s Guide by Herbert Schildt The copy constructor applies only to initializations The copy constructor does not apply to assignments The most common form of copy constructor is shown here classname const classname amp obj body of constructor Here obj is a reference to an object that is being used to initialize another object For example assuming a class called MyClass and y as an object of type MyClass then the following statements would invoke the MyClass copy constructor MyClass x y y explicitly initializing x func1 y y passed as a parameter y func2 y receiving a returned object In the first two cases a reference to y would be passed to the copy constructor In the third a reference to the object returned by func2 would be passed to the copy constructor Thus when an
285. ects In situations like this you may need to bypass the default bitwise copy by defining a custom assignment operator for the class as explained later in this module CRITICAL SKILL 9 3 Passing Objects to Functions 4 C A Beginner s Guide by Herbert Schildt An object can be passed to a function in the same way as any other data type Objects are passed to functions using the normal C call by value parameter passing convention This means that a copy of the object not the actual object itself is passed to the function Therefore changes made to the object inside the function do not affect the object used as the argument to the function The following program illustrates this point Pass an object to a function include lt iostream gt using namespace std class MyClass int val public MyClass int i val i int getval return val void setval int i val i void display MyClass ob display takes a MyClass object as a parameter cout lt lt ob getval lt lt n void change MyClass ob change also takes a MyClass f object as a parameter ob setval 100 no effect on argument cout lt lt Value of ob inside change display ob int main MyClass a 10 cout lt lt Value of a before calling change display a 1 Pass a MyClass object to display and changel change a cout lt lt V
286. ed In some implementations the field width must be set before each output If it isn t the default field width is used The streamsize type is defined as some form of integer by the compiler After you set a minimum field width when a value uses less than the specified width the field will be padded with the current fill character space by default to reach the field width If the size of the value exceeds the minimum field width then the field will be overrun No values are truncated When outputting floating point values in scientific notation you can determine the number of digits to be displayed after the decimal point by using the precision function Its prototype is shown here streamsize precision streamsize p Here the precision is set to p and the old value is returned The default precision is 6 In some implementations the precision must be set before each floating point output If you don t set it the default precision is used By default when a field needs to be filled it is filled with spaces You can specify the fill character by using the fill function Its prototype is char fill char ch After a call to fill ch becomes the new fill character and the old one is returned Here is a program that demonstrates these three functions 14 C A Beginner s Guide by Herbert Schildt Demonstrate width precision and fill include lt iostream gt using namespace std int main
287. ed inserter access the private elements of a class In the preceding program the variables x y and z were made public so that the inserter could access them But hiding data is an important part of OOP and forcing all data to be public is a serious inconsistency However there is a solution an inserter can be a friend of a class As a friend of the class for which it is defined it has access to private data Here the ThreeD class and sample program are reworked with the overloaded inserter declared as a friend Use a friend to overload lt lt include lt iostream gt using namespace std class ThreeD int x y Z 3 D coordinates now private public ThreeD int a int b int c x a y b Z CG friend ostream Soperator lt lt ostream amp stream ThreeD ThreeD inserter is now a friend and has Display X Y 4 coordinates ThreeD inserter access to private data ostream amp operator lt lt ostream amp stream ThreeD obj stream lt lt obj x lt lt stream lt lt obj y lt lt H stream lt lt obj z lt lt n return stream return the stream int main ThreeD a 1 2 3 b 3 4 5 e 5 6 7 cout lt lt a lt lt b lt lt c return Q Notice that the variables x y and z are now private to ThreeD but can still be directly accessed by the inserter Making inserters and extractors friends of the classes for which they are defined preserves the
288. efault constructor TwoDShape width height 0 0 strepy name unknown Constructor for TwoDShape TwoDShape double w double h char n width w height h strepy name n 38 C A Beginner s Guide by Herbert Schildt Construct object with equal width and height TwobShape double x char n width height x strepy name nm void showDim cout lt lt Width and height are lt lt width lt lt and lt lt height lt lt n accessor functions double getWidth return width double getHeight return height void setWidth double w width w void setHeight double h height h char getName return name area is now a pure virtual function _ _ _ ___ area is now a pure Virtual double area 0 virtual function t Triangle is derived from TwoDShape class Triangle public TwoDShape char style 20 now private public KR default constructor This automatically invokes the default constructor of TwoDShape Triangle strepy style unknown Constructor with three parameters Triangle char str double w double h TwoDShape w h triangle strepy style str Construct an isosceles triangle Triangle double x TwoDShape x triangle strepy style isosceles This now overrides area declared in TwoDShape double areal return getWidth getHeig
289. efer 6 What is a friend function 7 Show the general form used for overloading a binary member operator function 8 To allow operations involving a class type and a built in type what must you do 9 Can the be overloaded Can you change the precedence of an operator 10 For the Set class developed in Project 9 1 define lt and gt so that they determine if one set is a subset or a superset of another set Have lt return true if the left set is a subset of the set on the right and false otherwise Have gt return true if the left set is a superset of the set on the right and false otherwise 11 For the Set class define the amp so that it yields the intersection of two sets 12 On your own try adding other Set operators For example try defining so that it yields the symmetric difference between two sets The symmetric difference consists of those elements that the two sets do not have in common 55 C A Beginner s Guide by Herbert Schildt Module 10 Inheritance Virtual Functions and Polymorphism Table of Contents CRITICAL SKILL 10 1 Inheritance Fundamentals CRITICAL SKILL 10 2 Base Class Access Control CRITICAL SKILL 10 3 Using protected Members CRITICAL SKILL 10 4 Calling Base Class Constructors CRITICAL SKILL 10 5 Creating a Multilevel Hierarchy CRITICAL SKILL 10 6 Inheriting Multiple Base Classes CRITICAL SKILL 10 7 When Constructor and Destructor Functions Are Executed CRITICAL SKILL 10
290. elational and logical operators We will also examine the assignment operator The bitwise and other special operators are examined later CRITICAL SKILL 2 4 Arithmetic Operators C defines the following arithmetic operators Operator Meaning Addition Subtraction also unary minus i Multiplication i Division E3 Modulus Increment Decrement The operators and all work the same way in C as they do in algebra These can be applied to any built in numeric data type They can also be applied to values of type char 17 C A Beginner s Guide by Herbert Schildt The modulus operator yields the remainder of an integer division Recall that when is applied to an integer any remainder will be truncated for example 10 3 will equal 3 in integer division You can obtain the remainder of this division by using the operator For example 10 3 is 1 In C the can be applied only to integer operands it cannot be applied to floating point types The following program demonstrates the modulus operator Demonstrate the modulus operator include lt iostream gt using namespace std int main InG Xy y x 10 y 3 Cour ex ea yK Ye YW aR OY ee with a remainder of lt lt x y lt lt n x 1 y 2 COUE lt oe ae YY ey ee Uae Yh ee xe Pe ee OY e xa eM as yee YM ae YY eC Ke return QO The output is shown here 10 3 is 3 with a remainder of 1 L 7
291. elements from second set for int i 0 i lt ob2 len i newset newset ob2 members i return newset return updated set Set difference Set set operator Set ob2 Set newset this copy the first set Subtract elements from second set for int i 0 1 lt ob2 len i newset newset ob2 members i return newset return updated set Demonstrate the set class int main f construct 10 element empty set set sl Set sa Set s3 el sl AT si si B sl sl C cout lt lt sl after adding A B C p sl showset cout lt lt n cout lt lt Testing for membership using isMember n 1 sl isMember B cout lt lt B is a member of sl n else cout lt lt B is not a member of sl1 n tE sl isMember T cout lt lt T is a member of sl1 n 52 C A Beginner s Guide by Herbert Schildt else cout lt lt T is not a member of cout lt lt Nn sl sl B cout lt lt sl after sl sl B sl showset a si A cout lt lt sl after sl sl A sl showset sl sl C cout lt lt sl after al sl C sl showset cout sl s1 sl si s1 si m m n 4 AT B 4 Cl cout lt lt sl after adding A E C sl showset cout lt lt n s2 82 s2 82 S2 ap A f X f l TaT F cout lt lt s3 after adding A X W s2 showset co
292. eles triangle Triangle double x TwoDShape x triangle strcpy style lisosceles This now overrides area declared in TwoDShape double area 4 j Override areal J return getWidth getHeight 2 In Triangle void showStyle cout lt lt Triangle is lt lt style lt lt n 35 C A Beginner s Guide by Herbert Schildt A derived class of TwoDShape for rectangles class Rectangle public TwoDShape public f Construct a rectangle Rectangle double w double H TwoDShape w h rectangle Construct a square Rectangle double x TwoDShape x rectangle bool isSquare if getWidth getHeight return true return false This is another override of areal double area 4 Override areal agair return getWidth getHeight int main declare an array of pointers to TwoDShape objects TwobShape shapes 5 amp Triangle right 8 0 12 0 amp Rectangle 10 amp Rectangle 10 4 amp Triangle 7 0 amp TwoDShape 10 20 generic shapes 0 shapes 1 shapes 2 3 4 shapes shapes for int i 0 i lt 5 i cout lt lt object is lt lt shapes 1 gt getName lt lt n cout lt lt Area is lt lt shapes i gt area lt lt n X The proper version of area for each object is now called cout lt lt yn return QO The output from
293. employed your program automatically invokes an error handling routine when an exception occurs The principal advantage of exception handling is that it automates much of the error handling code that previously had to be entered by hand into any large program Exception Handling Fundamentals C exception handling is built upon three keywords try catch and throw In the most general terms program statements that you want to monitor for exceptions are contained in a try block If an exception that is an error occurs within the try block it is thrown using throw The exception is caught using catch and processed The following discussion elaborates upon this general description Code that you want to monitor for exceptions must have been executed from within a try block A function called from within a try block is also monitored Exceptions that can be thrown by the monitored code are caught by a catch statement that immediately follows the try statement in which the exception was thrown The general forms of try and catch are shown here try lI try block f catch typel arg catch block f catch type2 arg catch block catch fype3 arg catch block catch typeN arg catch block f The try block must contain the portion of your program that you want to monitor for errors This section can be as short as a few statements within one function or as all encompassing as a try block that encloses th
294. en an array allocated by new is released delete must be made aware that an array is being freed by using the As you will see in the next section this is especially important when you are allocating arrays of objects One restriction applies to allocating arrays They may not be given initial values That is you may not specify an initializer when allocating arrays Allocating Objects You can allocate objects dynamically by using new When you do this an object is created and a pointer is returned to it The dynamically created object acts just like any other object When it is created its constructor if it has one is called When the object is freed its destructor is executed Here is a program that creates a class called Rectangle that encapsulates the width and height of a rectangle Inside main an object of type Rectangle is created dynamically This object is destroyed when the program ends Allocate an object include lt iostream gt 31 C A Beginner s Guide by Herbert Schildt include lt new gt using namespace std class Rectangle int width int height public Rectangle int w int h width w height h cout lt lt Constructing lt lt width lt lt by lt lt height lt lt rectangle n Rectangle cout lt lt Destructing lt lt width lt lt by lt lt height lt lt rectangle n int area return width height ti int mai
295. ength by width The result is then output to the screen One more point before we move on It is possible to declare two or more variables using the same declaration statement Just separate their names by commas For example length width and area could have been declared like this int length width area all declared using one statement Declaring two or more variables in a single statement is very common in professionally written C code Progress Check 1 Must a variable be declared before it is used 2 Show how to assign the variable min the value 0O 3 Can more than one variable be declared in a single declaration statement 18 C A Beginner s Guide by Herbert Schildt Answer Key 1 Yes in C variables must be declared before they are used 2 min 0 3 Yes two or more variables can be declared in a single declaration statement CRITICAL SKILL 1 7 Reading Input from the Keyboard The preceding examples have operated on data explicitly specified in the program For example the area program just shown computes the area of a rectangle that is 7 by 5 and these dimensions are part of the program itself Of course the calculation of a rectangle s area is the same no matter what its size so the program would be much more useful if it would prompt the user for the dimensions of the rectangle allowing the user to enter them using the keyboard To enable the user to enter data into a program from t
296. ent exists in isolation Instead the components of the language work together This interrelatedness makes it difficult to discuss one aspect of C without involving others To help overcome this problem this module provides a brief overview of several C features including the general form of a C program some basic control statements and operators It does not go into too many details but rather concentrates on the general concepts common to any C program CRITICAL SKILL 1 1 A Brief History of C The history of C begins with C The reason for this is easy to understand C is built upon the foundation of C Thus C is a superset of C C expanded and enhanced the C language to support object oriented programming which is described later in this module C also added several other improvements to the C language including an extended set of library routines However much of the spirit and flavor of C is directly inherited from C Therefore to fully understand and appreciate C you need to understand the how and why behind C C The Beginning of the Modern Age of Programming The invention of C defines the beginning of the modern age of programming Its impact should not be underestimated because it fundamentally changed the way programming was approached and thought about Its design philosophy and syntax have influenced every major language since C was one of the major revolutionary forces in computing C was inv
297. ented and first implemented by Dennis Ritchie on a DEC PDP 11 using the UNIX operating system C is the result of a development process that started with an older language called BCPL BCPL was developed by Martin Richards BCPL influenced a language called B which was invented by Ken Thompson and which led to the development of C in the 1970s Prior to the invention of C computer languages were generally designed either as academic exercises or by bureaucratic committees C was different It was designed implemented and developed by real working programmers reflecting the way they approached the job of programming Its features were honed tested thought about and rethought by the people who actually used the language As a result C attracted many proponents and quickly became the language of choice of programmers around the world C grew out of the structured programming revolution of the 1960s Prior to structured programming large programs were difficult to write because the program logic tended to degenerate into what is known as spaghetti code a tangled mass of jumps calls and returns that is difficult to follow Structured languages addressed this problem by adding well defined control statements subroutines 2 C A Beginner s Guide by Herbert Schildt with local variables and other improvements Using structured languages it became possible to write moderately large programs Although there were other structured lang
298. enter the name The number is displayed 71 C A Beginner s Guide by Herbert Schildt A simple computerized telephone directory include lt iostream gt include lt cstdio gt using namespace std int main int i char str 80 char numbers 10 0 855 3322 555 8976 555 1037 555 1400 555 8873 Tom Mary Jon Rachel Sherry Enter name cin gt gt str cout lt lt For i 0 i lt 10 i 2 if stremp str numbers i cout lt lt Number is lt lt numbers i 1 lt lt break if i 10 cout lt lt Not found n return 0 Here is asample run Enter name Jon Number is 555 1037 This is an array of 10 strings each capable of holding up to 79 characters n Notice how the for loop increments its loop control variable i by 2 each time through the loop This is necessary because names and numbers alternate in the array 22 C A Beginner s Guide by Herbert Schildt Progress Check 1 Show how to initialize a four element array of int to the values 1 2 3 and 4 2 How can this initialization be rewritten char str 6 H e 1 ll oo O 3 Rewrite the following as an unsized array int nums 4 44 55 66 77 CRITICAL SKILL 4 8 Pointers The pointer is one of C s most powerful features It is also one of its most troublesome Despite their potential fo
299. er s Guide by Herbert Schildt CRITICAL SKILL 9 1 Overloading Constructors Although they perform a unique service constructors are not much different from other types of functions and they too can be overloaded To overload a class constructor simply declare the various forms it will take For example the following program defines three constructors Overload the constructor include lt iostream gt using namespace std class Sample public int x int y Overload the default constructor pample x y 0 Constructor with one parameter Sample int i x y i Overload the Sample constructor Constructor with two parameters Sample int i int j x 1 y j int main cample t invoke default constructor sample ti 5 use Sample int Sample t2 9 10 use Sample int int cout lt lt t r lt lt x lt lt E y T lt lt t y lt lt n cout lt lt tl x lt lt tl x lt lt tl y lt lt tl y lt lt n cout lt lt 2 x lt lt 2 e lt lt t2 y lt lt t2 y lt lt n return 0 The output is shown here Geos Uy eave 0 Cee oy whey o Cask 2y Dy 10 This program creates three constructors The first is a parameterless constructor which initializes both x and y to zero This constructor becomes the default constructor replacing the default constructor supplied automatically by C The second
300. er at the same time because i and ch overlay each other Instead your program can treat the information in the union as an integer or as a character at any time Thus a union gives you two or more ways to view the same piece of data You can declare a union variable by placing its name at the end of the union declaration or by using a separate declaration statement For example to declare a union variable called u_var of type utype you would write utype u_var In u_var both the short integer i and the character ch share the same memory location Of course i occupies two bytes and ch uses only one Figure 9 1 shows how i and ch both share the same address 23 C A Beginner s Guide by Herbert Schildt As far as C is concerned a union is essentially a class in which all elements are stored in the same location In fact a union defines a class type A union can contain constructors and destructors as well as member functions Because the union is inherited from C its members are public not private by default Here is a program that uses a union to display the characters that comprise the low and high order bytes of a short integer assuming short integers are two bytes Demonstrate a union include lt iostream gt using namespace std union u_type u_type short int a 1 a u_type char x char y void showchars cout lt lt ch 0 lt lt T cout lt lt ch 1 lt lt n short in
301. er has been declared it is not necessary to further qualify it or any of its members Thus ob1 run can be called directly the namespace has already been resolved There can be more than one namespace declaration of the same name In this case the namespaces are additive This allows a namespace to be split over several files or even separated within the same file For example namespace NS int i ff ei namespace NS int j I Here NS is split into two pieces but the contents of each piece are still within the same namespace that is NS One last point Namespaces can be nested That is one namespace can be declared within another using If your program includes frequent references to the members of a namespace having to specify the namespace and the scope resolution operator each time you need to refer to one quickly becomes 38 C A Beginner s Guide by Herbert Schildt tedious The using statement was invented to alleviate this problem The using statement has these two general forms using namespace name using name member In the first form name specifies the name of the namespace you want to access All of the members defined within the specified namespace are brought into view that is they become part of the current namespace and may be used without qualification In the second form only a specific member of the namespace is made visible For example assuming CounterNameSpace as just shown the followi
302. erbound which contain the upper and Demonstrate a namespace namespace CounterNameSpace Create a namespace called int upperbound CounterNameSpace int lowerbound class counter int count public counter int n 1f n lt upperbound count ri else count upperbound void reset int n 1f n lt upperbound count ri int run 1f count gt lowerbound return count else return lowerbound Here upperbound lowerbound and the class counter are part of the scope defined by the CounterNameSpace namespace Inside a namespace identifiers declared within that namespace can be referred to directly without any namespace qualification For example within CounterNameSpace the run function can refer directly to lowerbound in the statement if count gt lowerbound return count However since namespace defines a scope you need to use the scope resolution operator to refer to objects declared within a namespace from outside that namespace For example to assign the value 10 to upperbound from code outside CounterNameSpace you must use this statement CounterNameSpace upperbound 10 Or to declare an object of type counter from outside CounterNameSpace you will use a statement like this CounterNameSpace counter ob 36 C A Beginner s Guide by Herbert Schildt In general to access a member of a namespace from outside its namespace precede the member s name
303. ere can be situations in which the type of an object is unknown at compile time because the precise nature of that object is not determined until the program is executed As you know C implements polymorphism through the use of class hierarchies virtual functions and base class pointers A base class pointer can be used to point to objects of the base class or to any object derived from that base Thus it is not always possible to know in advance what type of object will be pointed to by a base pointer at any given moment This determination must be made at runtime using runtime type identification To obtain an object s type use typeid You must include the header lt typeinfo gt in order to use typeid Its most commonly used form is shown here typeid object Here object is the object whose type you will be obtaining It may be of any type including the built in types and class types that you create typeid returns a reference to an object of type type_info that describes the type of object The type_info class defines the following public members bool operator const type_info amp ob bool operator const type_info amp ob bool before const type_info amp ob const char name The overloaded and provide for the comparison of types The before function returns true if the invoking object is before the object used as a parameter in collation order This function is mostly for internal use only Its return value
304. erse is also true In C it is possible to index a pointer as if it were an array Here is an example It is a third version of the case changing program Index a pointer as if it were an array tinclude lt iostream gt include lt cctype gt using namespace std int main char p int i char str 80 This Is A Test cout lt lt Original string lt lt str lt lt n p str assign p the address of the start of the array now index p for i 0 p i i if isupper p i p i tolower p 1 else if islower p i 7 Access p as if it were an array p i toupper p il cout lt lt Inverted case string lt lt str return 0 The program creates a char pointer called p and then assigns to that pointer the address of the first element in str Inside the for loop p is indexed using the normal array indexing syntax This is perfectly valid because in C the statement pli is functionally identical to p i This further illustrates the close relationship between pointers and arrays 32 C A Beginner s Guide by Herbert Schildt Progress Check 1 Can an array be accessed through a pointer 2 Can a pointer be indexed as if it were an array 3 An array name used by itself with no index yields what l Yes an array can be accessed through a pointer 2 Yes a pointer can be indexed as if it Were an array 3 An array name used by itself with no inde
305. ersed tset a si siht Arrays of Pointers Pointers can be arrayed like any other data type For example the declaration for an int pointer array of size 10 is int pi 10 37 C A Beginner s Guide by Herbert Schildt Here pi is an array of ten integer pointers To assign the address of an int variable called var to the third element of the pointer array you would write int var pi 2 amp var Remember pi is an array of int pointers The only thing that the array elements can hold are the addresses of integer values not the values themselves To find the value of var you would write pi 2 Like other arrays arrays of pointers can be initialized A common use for initialized pointer arrays is to hold pointers to strings Here is an example that uses a two dimensional array of character pointers to implement a small dictionary Use a 2 D array of pointers to create a dictionary include lt iostream gt include lt cstring gt using namespace std This is a two dimensional array of char pointers which is used to point to pairs of strings int main char dictionary 2 _ o o pencil A writing instrument keyboard An input device rifle A shoulder fired firearm airplane A fixed wing aircraft network An interconnected group of computers Won nom F Fi char word 80 int i 38 C A Beginner s Guide by Herbert Schildt cout lt lt Enter word
306. es 1 10 A copy constructor makes a copy of an object It is called when one object initializes another Here is the general form classname const classname amp obj ii body of constructor i J When an object is returned by a function a temporary object is created as the return value This object is destroyed by the object s destructor after the value has been returned int sum return this 1i this j A structure is a class in which members are public by default A union is a class in which all data members share the same memory Union members are also public by default this refers to the object on which the function was called A friend function is a nonmember function that is granted access to the private members of the class for which it is a friend type classname operator type op2 l left operand passed via this To allow operations between a class type and a built in type you must use two friend operator functions one with the class type as the first parameter and one with the built in type as the first parameter No the cannot be overloaded No you cannot change the precedence of an operator 29 C A Beginner s Guide by Herbert Schildt Determine if one set is a subset of another bool Set operator lt Set ob2 1f len gt ob2 len return false obl has more elements for int 1 0 1 lt len i 1 ob2 find members i 1 return false return true
307. ess than or equal to Equal to Not equal to Logical Operators Operator Meaning amp amp AND I OR NOT Table 2 4 The Relational and Logical Operators in C The logical operators are used to support the basic logical operations AND OR and NOT according to the following truth table p p AND q p OR q NOT p True False False True False Here is a program that demonstrates several of the relational and logical operators Demonstrate the relational and logical operators include lt iostream gt using namespace std int main int i Jj bool bl b2 1 10 j 11 if i lt j cout lt lt i lt j n et lt Sour a aS an 71 C A Beginner s Guide by Herbert Schildt i j cout lt lt i j n if i j cout lt lt this won t execute n 1 gt J J cout lt lt this won t executen 1 gt J cout lt lt this won t execute n bl true b2 false if bl amp amp b2 cout lt lt this won t execute n if bl amp amp b2 cout lt lt bl amp b2 is true n if bL B2 cout lt lt bi D2 is trusa n return 0 The output from the program is shown here S ee J i lt j i j bl amp amp b2 is true b1 b2 is true Both the relational and logical operators are lower in precedence than the arithmetic operators This means that an expression like 10 gt 1 12 is evaluated as if it were written 10 gt 1 12 The result is o
308. est numObjects lt lt m in existence n n Test p new Test cout lt lt After allocating a Test object lt lt there are now lt lt Test numObjects lt lt m in existence n n delete p cout lt lt After deleting an object lt lt there are now lt lt a numObjects lt lt in existence n n return 0 The output from the program is shown here Constructing object 1 Constructing object 2 Constructing object 3 There are now 3 in existence Constructing object 4 After allocating a Test object there are now 4 in existence Destroying object 4 After deleting an object there are now 3 in existence Destroying object 3 Destroying object 2 Destroying object 1 45 C A Beginner s Guide by Herbert Schildt In the program notice how the static function numObjects is called In the first two calls it is called through its class name using this syntax Test numObjects In the third call it is invoked using the normal dot operator syntax on an object CRITICAL SKILL 12 7 Runtime Type Identification RTTI Runtime type information may be new to you because it is not found in non polymorphic languages such as C or traditional BASIC In non polymorphic languages there is no need for runtime type information because the type of each object is known at compile time that is when the program is written However in polymorphic languages such as C th
309. et feet feet feet feet feet feet feet feet feet feet feet feet feet feet feet feet feet feet feet feet feet feet feet feet feet feet feet is is 1s is is 1s is is is 1s is is rS 1s is is is is is is is is is 1s 1s 15 is 1s 1s 1s is WO WO O O NX N NNNNA A S amp S BSP WWW W O 10 LO 10 11 11 Tle Tee 04878 i 00 sO 0004 20041 20029 sool 8 7805 TE WAC 26097 6707 2120 s203 98934 9902 LOS meters meters meters Meter Meters Mevers meters me Cers 4878 meters 19208 Che wba 40244 nO Oe meters Mecers meters meters sUlz2 Meeere gol iO 62195 920083 ee N al eoa 84146 14634 paz meters meters meters meters meters meters meters meters 561 meters 10 061 meters meters meters meters meters meters meters meters 5 On your own try changing this program so that it prints a blank line every 25 lines CRITICAL SKILL 1 10 Introducing Functions A C program is constructed from building blocks called functions Although we will look at the function in detail in Module 5 a brief overview is useful now Let s begin by defining the term function a function is a subroutine that contains one or more C statements Each function has a name and this name is used to call the function To call a function simply specify its name in the source code of your program followed by parenthe
310. et of bytes If a mismatch is found the files differ If the end of each file is reached at the same time and if no mismatches have been found then the files are the same Step by Step 31 C A Beginner s Guide by Herbert Schildt 1 Create a file called CompFiles cpp Begin by adding these lines to CompFiles cpp tinclude lt iostream gt tinclude lt fstream gt using namespace std int main int argc register int i char argv unsigned char buf1 1024 buf2 1024 if arge 3 cout lt lt Usage return 1 j compfiles lt filel gt lt file2 gt n Notice that the names of the files to compare are specified on the command line 3 Add the code that opens the files for binary input operations as shown here ifstream fl argv 1 ios in 1os binary 1f f1 cout lt lt Cannot open first file n return 1 ifstream f2 argv 2 los in 1os binary 1f 2 cout lt lt Cannot open second file n return 1 The files are opened for binary operations to prevent the character translations that might occur in text mode 4 Add the code that actually compares the files as shown next cout lt lt Comparing files n do fl read char bufl sizeof buftl f2 read char bufz2 Sizeof buf2 1f fl geount 2 geount f cout lt lt Files are of differing sizes n fl close 32 C A Beginner s Guide by Herbert Schildt f2 cl
311. eue of integers will also work for a queue of characters and the same mechanism that maintains a linked list of mailing addresses will also maintain a linked list of auto part information When you create a generic class it can perform the operation you define such as maintaining a queue or a linked list for any type of data The compiler will automatically generate the correct type of object based upon the type you specify when the object is created The general form of a generic class declaration is shown here 19 C A Beginner s Guide by Herbert Schildt template lt class Ttype gt class class name body of class Here Ttype is the placeholder type name which will be specified when a class is instantiated If necessary you can define more than one generic data type using a comma separated list Once you have created a generic class you create a specific instance of that class using the following general form class name lt type gt ob Here type is the type name of the data that the class will be operating upon Member functions of a generic class are themselves automatically generic You need not use template to explicitly specify them as such Here is a simple example of a generic class A simple generic class include lt iostream gt using namespace std template lt class T gt class MyClass Declare a generic class T x Y Here T is the generic type public MyClass T a T b x a
312. ew style library is in the std namespace Recall that the std namespace is used by all of the Standard C libraries Since the old style I O library is now obsolete this book describes only the new I O library but most of the information is applicable to the old I O library as well CRITICAL SKILL 11 1 C Streams The most fundamental point to understand about the C I O system is that it operates on streams A stream is an abstraction that either produces or consumes information A stream is linked to a physical device by the C I O system All streams behave in the same manner even if the actual physical devices they are linked to differ Because all streams act the same the same 1 0 functions and operators can operate on virtually any type of device For example the same method that you use to write to the screen can be used to write to a disk or to the printer In its most common form a stream is a logical interface to a file As C defines the term file it can refer to a disk file the screen the keyboard a port a file on tape and so on Although files differ in form and capabilities all streams are the same The advantage to this approach is that to you the programmer one hardware device will look much like any other The stream provides a consistent interface A stream is linked to a file through an open operation A stream is disassociated from a file through a close operation There are two types of streams text
313. example if the string is I like C and the search string is like then the function returns a pointer to the in like Return a pointer include lt iostream gt using namespace std char get_substr char sub char str int main char substr substr get_substr three one two three four cout lt lt substring found lt lt substr return 0 Return pointer to substring or null if not found char get_substr char sub char ee int t get_substr returns char p p2 start a char pointer for t 0 str t t p amp str t reset pointers start p p2 sub while p2 amp amp p2 p check for substring p F p tt If at end of p2 i e substring then a match has been found if p2 return start return pointer to beginning of substring return 0 no match found Here is the output produced by the program substring found three four 25 C A Beginner s Guide by Herbert Schildt The main Function As you know the main function is special because it is the first function called when your program executes It signifies the beginning of your program Unlike some programming languages that always begin execution at the top of the program C begins every program with a call to the main function no matter where that function is located in the program However it is common for main to be t
314. exceptions rather than error codes For example both the Java and C languages rely heavily on exceptions using them to report most types of common errors such as an error opening a file or an arithmetic overflow Because C is derived from C it uses a blend of error codes and exceptions to report errors Thus many error conditions that relate to C library functions are reported using error return codes However in new code that you write you should consider using exceptions to report errors It is the way modern code is being written CRITICAL SKILL 12 2 Generic Functions A generic function defines a general set of operations that will be applied to various types of data The type of data that the function will operate upon is passed to it as a parameter Through a generic function a single general procedure can be applied to a wide range of data As you probably know many algorithms are logically the same no matter what type of data is being operated upon For example the Quicksort sorting algorithm is the same whether it is applied to an array of integers or an array of floats It is just that the type of data being sorted is different By creating a generic function you can define the nature of the algorithm independent of any data Once you have done this the compiler will automatically generate the correct code for the type of data that is actually used when you execute the function In essence when you create a generic function you
315. ey are mutually compatible This program gives the allocated integer an initial value of 87 29 C A Beginner s Guide by Herbert Schildt Initialize memory include lt iostream gt include lt new gt using namespace std int main int p try p new int 87 catch bad alloc xa cout lt lt Allocation Failure n return 1 cout lt lt At lt lt p lt lt cout lt lt is the value delete p return 0 Allocating Arrays You can allocate arrays using new by using this general form p_ var new array_ type size initialize to Initialize allocated memory Here size specifies the number of elements in the array To free an array use this form of delete delete p_var Here the informs delete that an array is being released For example the next program allocates a ten element integer array Allocate an array include lt iostream gt include lt new gt 30 C A Beginner s Guide by Herbert Schildt using namespace std int main int p i try f p new int 10 allocate 10 integer array catch bad alloc xa cout lt lt Allocation Failure n Allocate an array of int return 1 for i 0 1 lt 10 i pli j 1 for i 0 i lt 10 i cout lt lt p i lt lt delete p release the array 4 Release the array return 0 Notice the delete statement As just mentioned wh
316. ey work on a bit by bit level The exclusive OR XOR operates according to the following truth table P q p q oo b o h oo D 0 1 As the table indicates the outcome of an XOR is true only if exactly one of the operands is true it is false otherwise In terms of its most common usage you can think of the bitwise AND as a way to turn bits off That is any bit that is O in either operand will cause the corresponding bit in the outcome to be set to O For example 101 001l amp LOLOLOLO L000 OOLOD The following program demonstrates the amp by turning any lowercase letter into uppercase by resetting the sixth bit to 0 As the ASCII character set is defined the lowercase letters are the same as the uppercase ones except that the lowercase ones are greater in value by exactly 32 Therefore to transform a lowercase letter to uppercase just turn off the sixth bit as this program illustrates 17 C A Beginner s Guide by Herbert Schildt Uppercase letters using bitwise AND include lt iostream gt using namespace std int mairi char ch for int i 0 i lt 10 i ch a cout lt lt ch i This statement turns off the 6th bit ch ch amp 223 ch is now uppercase 4 Use the bitwise AND to turn off bit 6 cout lt lt ch lt lt cout lt lt n return 0 The output from this program is shown here aA bB cC dD eE fF gG hH il jJ The valu
317. f course false You can link any number of relational operations together using logical operators For example this expression joins three relational operations var gt 15 10 lt count amp amp 3 lt item The following table shows the relative precedence of the relational and logical operators Highest Lowest Project 2 2 Construct an XOR Logical Operation C does not define a logical operator that performs an exclusive OR operation usually referred to as XOR The XOR is a binary operation that yields true when one and only one operand is true It has this truth table 22 C A Beginner s Guide by Herbert Schildt p q p XOR q False False True True False Some programmers have called the omission of the XOR a flaw Others argue that the absence of the XOR logical operator is simply part of C s streamlined design which avoids redundant features They point out that it is easy to create an XOR logical operation using the three logical operators that C does provide In this project you will construct an XOR operation using the amp amp and operators You can decide for yourself if the omission of an XOR logical operator is a design flaw or an elegant feature Step by Step 1 Create a new file called XOR cpp 2 Assuming two Boolean values p and q a logical XOR is constructed like this Dp q amp amp p amp amp q Let s go through this carefully First p is ORed with q If
318. f ident for int 1 0 1 lt ident i cout lt lt if b cout lt lt true else cout lt lt false void print int i int ident if ident for int 1 0 1 lt ident i cout lt lt cout lt lt 1 void print long 1 int ident 1 ident for int 1 0 1 lt ident i cout lt lt cout lt lt i void print char ch int ident if ident for int i 0 i lt ident i cout lt lt 18 C A Beginner s Guide by Herbert Schildt cout lt lt ch void print char str int ident 1 ident for int 1 0 1 lt ident i cout lt lt cout lt lt str void print double d int ident 1 ident for int 1 0 1 lt ident i cout lt lt cout lt lt d myfunc x myfune x 19 myfune x 19 35 10 Function overloading can introduce ambiguity when the compiler cannot decide which version of the function to call This can occur when automatic type conversions are involved and when default arguments are used Module 7 More Data Types and Operators 1 static int test 100 2 True The volatile specifier tells the compiler that a variable might be changed by forces outside the program 3 Ina multifile project to tell one file about a global variable declared in another file use extern 4 The most important attribute of a static local variable is that it holds its value between function calls 5
319. f bp 10 10 10 Value of c after c a be Ll 12 13 Value of c after c at bte 22 24 26 Value of c after c b a 1 2 3 30 C A Beginner s Guide by Herbert Schildt Value of b after c b a 1 2 3 As you examined the program you may have been surprised to see that both operator functions have only one parameter each even though they overload binary operations The reason for this apparent contradiction is that when a binary operator is overloaded using a member function only one argument is explicitly passed to it The other argument is implicitly passed using the this pointer Thus in the line temp x X Op2 x the x refers to this gt x which is the x associated with the object that invokes the operator function In all cases it is the object on the left side of an operation that causes the call to the operator function The object on the right side is passed to the function In general when you use a member function no parameters are used when overloading a unary operator and only one parameter is required when overloading a binary operator You cannot overload the ternary operator In either case the object that invokes the operator function is implicitly passed via the this pointer To understand how operator overloading works let s examine the preceding program carefully beginning with the overloaded operator When two objects of type ThreeD are operated on by the operator the magnitudes of t
320. f bytes from the specified origin The seekp function moves the associated file s current put pointer offset number of bytes from the specified origin Generally random access I O should be performed only on those files opened for binary operations The character translations that may occur on text files could cause a position request to be out of sync with the actual contents of the file 35 C A Beginner s Guide by Herbert Schildt The following program demonstrates the seekp function It allows you to specify a filename on the command line followed by the specific byte that you want to change in the file The program then writes an X at the specified location Notice that the file must be opened for read write operations Demonstrate random access include lt iostream gt include lt fstream gt include lt cestdlib gt using namespace std int main int argc char argv 1f arge 3 cout lt lt Usage CHANGE lt filename gt lt byte gt n return 1 fstream out argv 1 ios in ios out ios binary i1f out cout lt lt Cannot open file n return 1 out seekp atoi argv 2 ios beg out put X Seek to a specific byte within the file out close This moves the put pointer return 0 The next program uses seekg It displays the contents of a file beginning with the location you specify on the command line 36 C A Beginner s Guide by Herbert Schildt D
321. f programming tasks to which C can be applied These operators include the bitwise shift and sizeof operators 1 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 7 1 The const and volatile Qualifiers C has two type qualifiers that affect the ways in which variables can be accessed or modified These modifiers are const and volatile Formally called the cv qualifiers they precede the base type when a variable is declared const A variable declared with the const modifier cannot have its value changed during the execution of your program Thus a const variable isn t really variable You can give a variable declared as const an initial value however For example const int max_users 9 creates an int variable called max_users that contains the value 9 This variable can be used in expressions like any other variable but its value cannot be modified by your program A common use of const is to create a named constant Often programs require the same value for many different purposes For example a program might have several different arrays that are all the same size In this case you can specify the size of the arrays using a const variable The advantage to this approach is that if the size needs to be changed at a later date you need change only the value of the const variable and then recompile the program You don t need to change the size in each array declaration This approach avoids errors and is
322. f their argument Thus overloading supports the polymorphic concept of one interface multiple methods The following program demonstrates this Create various versions of the neg function tinclude lt iostream gt using namespace std int neg int n neg for int double neg double n neg for double long neg long ri neg for long int main cout lt lt neg 10 lt lt neg 10 lt lt n cout lt lt neg 9L lt lt neg 9L lt lt n cout lt lt neg 11 23 lt lt neg 11 23 lt lt n return OQ neg for int int neg int n return n negq for double double neg double n return n neg for long long neg long r return n The output is shown here neg 10 10 neg 9L 9 15 C A Beginner s Guide by Herbert Schildt neg 11 23 11 23 This program creates three similar but different functions called neg each of which returns the absolute value of its argument The compiler knows which function to use in each given situation because of the type of the argument The value of overloading is that it allows related sets of functions to be accessed using a common name Thus the name neg represents the general action that is being performed It is left to the compiler to choose the right specific version for a particular circumstance You the programmer need only remember the general action being performed T
323. f type bool char int long char and double but you can add other types on your own Step by Step 1 Create a file called Print cpp 20 C A Beginner s Guide by Herbert Schildt 2 Begin the project with these lines Project 6 1 Create overloaded print and printin functions that display various types of data i include lt iostream gt using namespace std 3 Add the prototypes for the print and println functions as shown here These output a newline void printin bool b void printin int i void printlin long i void println char ch void printlin char str void printin double d These functions do not output a newline void print bool b void print int i void print long i void print char ch void print char str void print double d 4 Implement the printin functions as shown here Here are the println functions void println bool b if b cout lt lt true n else cout lt lt false n void println int 1 cout lt lt i lt lt n 71 C A Beginner s Guide by Herbert Schildt void printlin long i cout lt lt i lt lt n void println char ch cout lt lt ch lt lt n void printin char str cout lt lt str lt lt n void println double d cout lt lt d lt lt n Notice that each function appends a newline character to the output Also notice that
324. fect the argument Using a reference parameter allows the function to increment or decrement the object used as an operand When a friend is used for overloading the increment or decrement operators the prefix form takes one parameter which is the operand The postfix form takes two parameters The second parameter is an integer which is not used Here is the way to overload both forms of a friend operator function for the ThreeD class Overload prefix using a friend function This requires the use of a reference parameter ThreeD operator ThreeD amp op1 op1l x opl y opl z return opl 42 C A Beginner s Guide by Herbert Schildt Overload postfix using a friend function This requires the use of a reference parameter ThreeD operator ThreeD amp opl int notused ThreeD temp opil opl x opl y opl z return temp Progress Check 1 How many parameters does a nonmember binary operator function have 2 When using a nonmember operator function to overload the operator how must the operand be passed 3 One advantage to using friend operator functions is that it allows a built in type such as int to be used as the left operand True or false Operator Overloading Tips and Restrictions The action of an overloaded operator as applied to the class for which it is defined need not bear any relationship to that operator s default usage as applied to C s built
325. fer 8 On your own try enhancing CompFiles with various options For example add an option that ignores the case of letters Another idea is to have CompFiles display the position within the file where the files differ CRITICAL SKILL 11 11 Random Access So far files have been read or written sequentially but you can also access a file in random order In C s I O system you perform random access using the seekg and seekp functions Their most common forms are shown here istream amp seekg off type offset seekdir origin ostream amp seekp oft type offset seekdir origin Here Value Meaning los beg Beginning of file los cur Current location los end End of file off_type is an integer type defined by ios that is capable of containing the largest valid value that offset can have seekdir is an enumeration that has these values The C I O system manages two pointers associated with a file One is the get pointer which specifies where in the file the next input operation will occur The other is the put pointer which specifies where in the file the next output operation will occur Each time an input or an output operation takes place the appropriate pointer is automatically advanced Using the seekg and seekp functions it is possible to move this pointer and access the file in a non sequential fashion The seekg function moves the associated file s current get pointer offset number o
326. first you might think that it is a serious restriction that derived classes do not have access to the private members of base classes because it would prevent the use of private members in many situations Fortunately this is not the case because C provides various solutions One is to use protected members which is described in the next section A second is to use public functions to provide access to private data As you have seen in the preceding modules C programmers typically grant access to the private members of a class through functions Functions that provide access to private data are called accessor functions Here is a rewrite of the TwoDShape class that adds accessor functions for width and height 5 C A Beginner s Guide by Herbert Schildt Access private data through accessor functions include lt iostream gt include lt estring gt using namespace std A class for two dimensional objects class TwoDShape these are private double width double height public void showDim cout lt lt Width and height are lt lt width lt lt and lt lt height lt lt n accessor functions double getWidth return width double getHeight return height void setWidth double w width w void setHeight double h height h The accessor functions for width and height Triangle is derived from TwoDShape class Triangle public TwoDShape public
327. fly introduced here because we will be using them to write sample programs The if Statement You can selectively execute part of a program through the use of C s conditional statement the if The if statement works in C much like the IF statement in any other language For example it is syntactically identical to the if statements in C Java and C Its simplest form is shown here if condition statement where condition is an expression that is evaluated to be either true or false In C true is nonzero and false is zero If the condition is true then the statement will execute If it is false then the statement will 26 C A Beginner s Guide by Herbert Schildt not execute For example the following fragment displays the phrase 10 is less than 11 on the screen because 10 is less than 11 if 10 lt 11 cout lt lt 10 is less than 11 However consider the following 1 10 gt 11 cout lt lt this does not display In this case 10 is not greater than 11 so the cout statement is not executed Of course the operands inside an if statement need not be constants They can also be variables C defines a full complement of relational operators that can be used in a conditional expression They are shown here lt Less than or equal gt Equalto o pe Notequal o Notice that the test for equality is the double equal sign Here is a program that illustrates the if statement 14 Demonstrate t
328. following fragment is compiled only if DEBUG is not defined i defined DEBUG Gout lt lt Final Version n endif line The line directive is used to change the contents of __LINE__ and___FILE__ which are predefined macro names _ _LINE_ _ contains the line number of the line currently being compiled and _ _FILE_ _ contains the name of the file being compiled The basic form of the line command is line number filename Here number is any positive integer and the optional filename is any valid file identifier The line number becomes the number of the current source line and the filename becomes the name of the source file line is primarily used for debugging purposes and for special applications oragma The pragma directive is an implementation defined directive that allows various instructions defined by the compiler s creator to be given to the compiler The general form of the pragma directive is pragma name Here name is the name of the pragma you want If the name is unrecognized by the compiler then the pragma directive is simply ignored and no error results To see what pragmas your compiler supports check its documentation You might find some that are valuable to your programming efforts Typical pragmas include those that determine what compiler warning messages are issued how code is generated and what library is linked The and Preprocessor Operators C supports two preproce
329. follows that style and it is recommended that you do so as well Using this style you indent one level after each opening brace and move back out one level after each closing brace There are certain statements that encourage some additional indenting these will be covered later 32 C A Beginner s Guide by Herbert Schildt Progress Check 1 How isa block of code created What does it do 2 In C statements are terminated by a 3 All C statements must start and end on one line True or false Answer Key 1 A block is started by a It is ended by a A block creates a logical unit of code 2 semicolon 3 False Project 1 2 Generating a Table of Feet to Meter Conversions This project demonstrates the for loop the if statement and code blocks to create a program that displays a table of feet to meters conversions The table begins with 1 foot and ends at 100 feet After every 10 feet a blank line is output This is accomplished through the use of a variable called counter that counts the number of lines that have been output Pay special attention to its use Step by Step 1 Create a new file called FtoMTable cpp 2 Enter the following program into the file 33 C A Beginner s Guide by Herbert Schildt Project 1 2 This program displays a conversion table of feet to meters Call this program FtoMTable cpp we F j include lt iostream gt using namespace std int maini f double f holds
330. ft of the operator is an integer a built in type for which no operation involving an integer and an object of T s type is defined The solution to the preceding problem is to overload the using two friend functions In A Closer Look at Classes this case the operator function is explicitly passed both arguments and is invoked like any other overloaded function based upon the types of its arguments One version of the operator function handles object integer and the other handles integer object Overloading the or any other binary operator using friend functions allows a built in type to occur on the left or right side of the operator The following program illustrates this technique It defines two versions of operator for objects of type ThreeD Both add an integer value to each of ThreeD s instance variables The integer can be on either the left or right side of the operator Overload for integer object and object integer include lt iostream gt using namespace std class ThreeD int x y Z 3 D coordinates public ThreeD x y z 0 ThreeD int i int j int k x 1 y j z K friend ThreeD operator ThreeD opl int op2 Thies ENEE friend ThreeD operator int opl ThreeD op2 int and int ob 40 C A Beginner s Guide by Herbert Schildt void show j This allows ThreeD int ThreeD operator ThreeD opl int op2 ThreeD temp temp x opl x op temp
331. ft right for t 0 t lt 8 t i i gt gt 1 Right shift i one position show_binary i return OQ Display the bits within a byte void show_binary unsigned int u int t 23 C A Beginner s Guide by Herbert Schildt for t 128 t gt 0 t t 2 1f u amp t cout lt lt 1 else cout lt lt 0 cout lt lt n This program produces the following output 0000000 1 0000001 0 000001 0 0 000010 0 0 000100 0 0 001000 0 0 010000 0 0 100000 0 0 100000 0 0 010000 0 0 0012000 0 0 000100 0 0 000010 0 0 09000010 0 000000 1 0 0000000 1 Progress Check 1 What are the bitwise operators for AND OR NOT and XOR 2 A bitwise operator works on a bit by bit basis True or false 3 Given an integer called x show how to left shift x two places Create Bitwise Rotation Functions Although C provides two shift operators it does not define a rotate operator A rotate is similar to a shift except that the bit shifted off one end is inserted onto the other end Thus bits are not lost just moved There are both left and right rotations For example 1010 0000 rotated left one place is 0100 0001 The same value rotated right one place is 0101 OOOO In each case the bit shifted out is inserted onto the other end Although the lack of rotation operators may seem to be a 24 C A Beginner s Guide by Herbert Schildt flaw in C s otherwise exemplary complement of bitwise operators
332. g situations As such the goto is not used in this book outside of this section The chief concern most programmers have about the goto is its tendency to clutter a program and render it nearly unreadable However there are times when the use of the goto can clarify program flow rather than confuse it The goto requires a label for operation A label is a valid C identifier followed by a colon Furthermore the label must be in the same function as the goto that uses it For example a loop from 1 to 100 could be written using a goto and a label as shown here x 1 loopl re Atti if x lt 100 goto loopl Execution jumps to loopl One good use for the goto is to exit from a deeply nested routine For example consider the following code fragment 35 C A Beginner s Guide by Herbert Schildt for for d while 1f goto stop stop cout lt lt Error in program n Eliminating the goto would force a number of additional tests to be performed A simple break statement would not work here because it would only cause the program to exit from the innermost loop Module 3 Mastery Check 1 Write a program that reads characters from the keyboard until a S is typed Have the program count the number of periods Report the total at the end of the program 2 Inthe switch can the code sequence from one case run into the next Explain 3 Show the general form of the if else if ladder
333. gram is called add C gt add 100 2 231 Progress Check 1 What are the two parameters to main usually called Explain what each contains 2 What is always the first command line argument 3 A numeric command line argument is passed as string True or false CRITICAL SKILL 5 11 Function Prototypes Function prototypes were discussed briefly at the beginning of this module Now it is time to explain them more fully In C all functions must be declared before they are used Typically this is accomplished by use of a function prototype Prototypes specify three things about a function e Its return type e The type of its parameters e The number of its parameters e Prototypes allow the compiler to perform three important operations 29 C A Beginner s Guide by Herbert Schildt e They tell the compiler what type of code to generate when a function is called Different return types must be handled differently by the compiler e They allow C to find and report any illegal type conversions between the type of arguments used to call a function and the type definition of its parameters e They allow the compiler to detect differences between the number of arguments used to call a function and the number of parameters in the function The general form of a function prototype is shown here It is the same as a function definition except that no body is present type func name type parm_namel1 type parm_name2 type parm
334. gram is shown here 5 19 Destructing object whose x value is 19 Destructing object whose x value is 5 In this version of the program the MyClass constructor defines one parameter called i which is used to initialize the instance variable x Thus when the line MyClass ob1 5 executes the value 5 is passed to i which is then assigned to x 18 C A Beginner s Guide by Herbert Schildt Unlike constructors destructors cannot have parameters The reason for this is easy to understand there is no means by which to pass arguments to an object that is being destroyed Although the situation is rare if your object needs to be passed some data just before its destructor is called you will need to create a specific variable for this purpose Then just prior to the object s destruction you will need to set that variable Adding a Constructor to the Vehicle Class We can improve the Vehicle class by adding a constructor that automatically initializes the passengers fuelcap and mpg fields when an object is constructed Pay special attention to how Vehicle objects are created Add a constructor to the vehicle class include lt iostream gt using namespace std Declare the Vehicle class class Vehicle f public 19 C A Beginner s Guide by Herbert Schildt int passengers number of passengers int fuelcap fuel capacity in gallons int mpg fuel consumption in miles per gallon This is a co
335. gt gt i cout lt lt i return O Remember that it is crucial that your manipulator return stream If this is not done then your manipulator cannot be used in a chain of input or output operations Progress Check 1 What does endl do 2 What does ws do 3 Isan I O manipulator used as part of a larger I O expression File I O You can use the C I O system to perform file I O To perform file I O you must include the header lt fstream gt in your program It defines several important classes and values CRITICAL SKILL 11 7 Opening and Closing a File In C a file is opened by linking it to a stream As you know there are three types of streams input output and input output To open an input stream you must declare the stream to be of class ifstream 20 C A Beginner s Guide by Herbert Schildt To open an output stream it must be declared as class ofstream A stream that will be performing both input and output operations must be declared as class fstream For example this fragment creates one input stream one output stream and one stream capable of both input and output ifstream in input ofstream out output fstream both input and output Once you have created a stream one way to associate it with a file is by using open This function is a member of each of the three stream classes The prototype for each is shown here void ifstream open const char ilename ios openmode mode 108
336. h the numbers 1 through 10 int i 10 1 2 3 4 5 6 7 8 9 10 This means that i 0 will have the value 1 and i 9 will have the value 10 Character arrays that will hold strings allow a shorthand initialization that takes this form char array_name size string For example the following code fragment initializes str to the string C char str 4 C This is the same as writing char str 4 C O Because strings in C must end with a null you must make sure that the array you declare is long enough to include it This is why str is four characters long in these examples even though C is only three When a string constant is used the compiler automatically supplies the null terminator Multidimensional arrays are initialized in the same way as one dimensional arrays For example the following program initializes an array called sqrs with the numbers 1 through 10 and their squares 17 C A Beginner s Guide by Herbert Schildt int sqrs 10 2 4 L 13 Zp Aa oe oy 4 16 Dy Ay by SO ly 49 8 64 Oy Oy LOG L010 F3 Examine Figure 4 1 to see how the sars array appears in memory Left index Figure 4 1 The initialized sqrs array Left index 18 C A Beginner s Guide by Herbert Schildt When initializing a multidimensional array you may add braces around the initializers for each dimension This is called subaggregate grouping For example here is
337. handled by the linker By default functions are linked as C functions but a linkage specification lets you link a function for a different type of language The general form of a linkage specifier is shown here extern language function prototype where language denotes the desired language For example this specifies that myCfunc will have C linkage extern C void myCfunc All C compilers support both C and C linkage Some may also allow linkage specifiers for FORTRAN Pascal or BASIC You will need to check the documentation for your compiler You can specify more than one function at a time using this form of the linkage specification extern language prototypes I For most programming tasks you won t need to use a linkage specification CRITICAL SKILL 7 3 static Variables Variables of type static are permanent variables within their own function or file They differ from global variables because they are not known outside their function or file Because static affects local variables differently than it does global ones local and global variables will be examined separately Static Local Variables When the static modifier is applied to a local variable permanent storage for the variable is allocated in much the same way that it is for a global variable This allows a static variable to maintain its value between function calls That is its value is not lost when the function returns unlike t
338. he first function in your program so that it can be easily found There can be only one main in a program If you try to include more than one your program will not know where to begin execution Actually most compilers will catch this type of error and report it As mentioned earlier since main is predefined by C it does not require a prototype CRITICAL SKILL 5 10 Pass Command Line Arguments to main Sometimes you will want to pass information into a program when you run it This is generally accomplished by passing command line arguments to main A command line argument is the information that follows the program s name on the command line of the operating system In Windows the Run command also uses a command line For example you might compile C programs from the command line by typing something like this cl prog name where prog name is the program you want compiled The name of the program is passed into the C compiler as a command line argument C defines two built in but optional parameters to main They are argc and argv and they receive the command line arguments These are the only parameters defined by C for main However other arguments may be supported in your specific operating environment so you will want to check your compiler s documentation Let s now look at argc and argv more closely NOTE Technically the names of the command line parameters are arbitrary you can use any n
339. he if include lt iostream gt using namespace std 27 C A Beginner s Guide by Herbert Schildt int maini int a b c A 2 b 3 ifia lt bi cout lt lt a is less than bin An If statement this won t display anything ifia Bb cout lt lt you won t see this n cout lt lt n f f e contains 1 c a Bb cout lt lt o contains l n ific gt 0 cout lt lt c is non negative n if c lt 0 cout lt lt c is negativen cout lt lt An e b a c now contains 1 cout lt lt o contains 1 n if e gt 0 cout lt lt o is non negative n ifc lt 0 cout lt lt c is negative n return H The output generated by this program is shown here a is less than b contains l c is negative C contains 1 c is non negative The for Loop You can repeatedly execute a sequence of code by creating a loop C supplies a powerful assortment of loop constructs The one we will look at here is the for loop If you are familiar with C or Java then you will be pleased to know that the for loop in C works the same way it does in those languages The simplest form of the for loop is shown here for initialization condition increment statement Here initialization sets a loop control variable to an initial value condition is an expression that is tested each time the loop repeats As long as condition is true nonzero the
340. he keyboard you will use the gt gt operator This is the C input operator To read from the keyboard use this general form cin gt gt var Here cin is another predefined identifier It stands for console input and is automatically supplied by C By default cin is linked to the keyboard although it can be redirected to other devices The variable that receives input is specified by var Here is the area program rewritten to allow the user to enter the dimensions of the rectangle 19 C A Beginner s Guide by Herbert Schildt F sh j An interactive program that computes the area of a rectangle tinelude lt iostream gt using namespace std int mainii int length this declares a variable int width this declares another variable cout lt lt Enter the length cin gt gt length input the length Input the value of length from the keyboard cout lt lt Enter the width cin gt gt width input the width Input the valve of width from the keyboard cout lt lt The area is cout lt lt length width display the area return OU Here is asample run Enter the length 8 Enter the width 3 The area is 24 Pay special attention to these lines cout lt lt Enter the length cin gt gt length input the length The cout statement prompts the user The cin statement reads the user s response storing the value in length Thus
341. he value of a 6 C A Beginner s Guide by Herbert Schildt normal local variable The key difference between a static local variable and a global variable is that the Static local variable is known only to the block in which it is declared To declare a static variable precede its type withthe word static For example this statement declares count as a Static variable static int count A static variable may be given an initial value For example this statement gives count an initial value of 200 static int count 200 Local static variables are initialized only once when program execution begins not each time the block in which they are declared is entered The static local variable is important to functions that must preserve a value between calls If static variables were not available then global variables would have to be used opening the door to possible side effects To see an example of a static variable try this program It keeps a running average of the numbers entered by the user 7 C A Beginner s Guide by Herbert Schildt Compute a running average of numbers entered by the user include lt iostream gt using namespace std int running_avg int 1 int main int num do cout lt lt Enter numbers 1 to quit cin gt gt num if num 1 cout lt lt Running average is lt lt running_avg num cout lt lt n while num gt 1 return 0
342. heir respective coordinates are added together as shown in operator Notice however that this function does not modify the value of either operand Instead an object of type ThreeD which contains the result of the operation is returned by the function To understand why the operation does not change the contents of either object think about the standard arithmetic operation as applied like this 10 12 The outcome of this operation is 22 but neither 10 nor 12 is changed by it Although there is no rule that prevents an overloaded operator from altering the value of one of its operands it is best for the actions of an overloaded operator to be consistent with its original meaning Notice that operator returns an object of type ThreeD Although the function could have returned any valid C type the fact that it returns a ThreeD object allows the operator to be used in compound expressions such as a b c Here a b generates a result that is of type ThreeD This value can then be added to c Had any other type of value been generated by a b such an expression would not work In contrast with the operator the assignment operator does indeed cause one of its arguments to be modified This is after all the very essence of assignment Since the operator function is called by the object that occurs on the left side of the assignment it is this object that is modified by the assignment operation Most often the return val
343. her point Even though TwoDShape is a base for Triangle it is also a completely independent stand alone class Being a base class for a derived class does not mean that the base class cannot be used by itself The general form for inheritance is shown here class derived class access base class body of derived class Here access is optional However if present it must be public private or protected You will learn more about these options later in this module For now all inherited classes will use public Using public means that all the public members of the base class will also be public members of the derived class Triangle Figure 10 1 A conceptual depiction of the Triangle class A major advantage of inheritance is that once you have created a base class that defines the attributes common to a set of objects it can be used to create any number of more specific derived classes Each derived class can precisely tailor its own classification For example here is another class derived from TwoDShape that encapsulates rectangles A derived class of TwoDShape for rectangles class Rectangle public TwoDShape public bool isSquare if width height return true return false double area return width height The Rectangle class includes TwoDShape and adds the functions isSquare which determines if the rectangle is square and area which computes the area of a rectangle 4 C A Beg
344. herefore through the application of polymorphism three things to remember have been reduced to one Although this example is fairly simple if you expand the concept you can see how overloading can help you manage greater complexity Another advantage to function overloading is that it is possible to define slightly different versions of the same function that are specialized for the type of data upon which they operate For example consider a function called min that determines the minimum of two values It is possible to create versions of min that behave differently for different data types When comparing two integers min returns the smallest integer When two characters are compared min could return the letter that is first in alphabetical order ignoring case differences In the ASCII sequence uppercase characters are represented by values that are 32 less than the lowercase letters Thus ignoring case would be useful when alphabetizing When comparing two pointers it is possible to have min compare the values pointed to by the pointers and return the pointer to the smallest value Here is a program that implements these versions of min Create various versions of min include lt iostream gt using namespace std int min int a int bb min for ints char min char a char b min for chars int min int a int b min for int pointers int main int i 10 j 22 cout gZ min X a
345. hich it is defined However a virtual function can be a friend of another class Also it is permissible for destructors but not constructors to be virtual Because of the restrictions and differences between overloading normal functions and redefining virtual functions the term overriding is used to describe the redefinition of a virtual function Virtual Functions Are Inherited Once a function is declared as virtual it stays virtual no matter how many layers of derived classes it may pass through For example if D2 is derived from D1 instead of B as shown in the next example then who is still virtual 31 C A Beginner s Guide by Herbert Schildt Derive from Dl not B class D2 public D1 public void who define who relative to second_d cout lt lt Second derivation n t When a derived class does not override a virtual function then the function as defined in the base class is used For example try this version of the preceding program Here D2 does not override who include lt iostream gt using namespace std class E public virtual void who cout lt lt Basen class D1 public B public void who cout lt lt First derivation n d class D2 public B who not defined 4 D does not override whol int main E base_obj B p D1 Dl_obj D2 D2_obj p amp base_obj p gt who access E s who p a
346. howpoint showpos skipws unitbuf Uppercase 2 What is an extractor 3 Why are friend functions often used for inserter or extractor functions Formatted I O Up to this point the format for inputting or outputting information has been left to the defaults provided by the C I O system However you can precisely control the format of your data in either of two ways The first uses member functions of the ios class The second uses a special type of function called a manipulator We will begin by looking at formatting using the ios member functions CRITICAL SKILL 11 4 Formatting with the ios Member Functions Each stream has associated with it a set of format flags that control the way information is formatted by a stream The ios class declares a bitmask enumeration called fmtflags in which the following values are defined Technically these values are defined within ios_base which is a base class for ios 10 C A Beginner s Guide by Herbert Schildt These values are used to set or clear the format flags Some older compilers may not define the fmtflags enumeration type In this case the format flags will be encoded into a long integer When the skipws flag is set leading whitespace characters spaces tabs and newlines are discarded when performing input on a stream When skipws is cleared whitespace characters are not discarded When the left flag is set output is left justified When right is set ou
347. ht 2 39 C A Beginner s Guide by Herbert Schildt void showStyle cout lt lt Triangle is lt lt style lt lt n A derived class of TwoDShape for rectangles class Rectangle public TwoDShape public f Construct a rectangle Rectangle double w double H TwobShape w h rectangle Construct a square Rectangle double x TwobDShape x rectangle bool isSquare if getWidth getHeight return true return false This is another override of area double area return getWidth getHeight int main declare an array of pointers to TwoDShape objects TwobsShape shapes 4 shapes 0 amp Triangle right 8 0 12 0 Shapes 1 amp Rectangle 10 Shapes 2 amp Rectangle 10 4 shapes 3 amp Triangle 7 0 for int i 0 i lt 4 i cout lt lt object is lt lt shapes 1 gt getName lt lt n cout lt lt Area is lt lt shapes 1 gt area lt lt n cout lt lt yn return QO If a class has at least one pure virtual function then that class is said to be abstract An abstract class has one important feature there can be no objects of that class To prove this to yourself try removing the 40 C A Beginner s Guide by Herbert Schildt override of area from the Triangle class in the preceding program You will receive an error when you try to create an instance of Tria
348. ilers will implement new in a different way When C was first invented new returned a null pointer on failure Later this was changed so that new throws an exception on failure as just described If you are using an older compiler check your compiler s documentation to see precisely how it implements new Since Standard C specifies that new generates an exception on failure this is the way the code in this book is written If your compiler handles an allocation failure differently then you will need to make the appropriate changes Here is a program that allocates memory to hold an integer Demonstrate new and delete include lt iostream gt include lt new gt using namespace std int main int p Allocate an int try p new int allocate space for an int cateh bad_alloc xa o cout lt lt Allocation Failure n rena 1 Watch for an allocation failure p 100 cout lt lt At lt lt p lt lt cout lt lt is the value lt lt p lt lt n delete p Release the allocated memory return 0 This program assigns to p an address in the heap that is large enough to hold an integer It then assigns that memory the value 100 and displays the contents of the memory on the screen Finally it frees the dynamically allocated memory The delete operator must be used only with a valid pointer previously allocated by using new Using any other type of pointer w
349. in binary using the show_binary function developed earlier include lt iostream gt using namespace std void show_binary unsigned int u int main unsigned u cout lt lt Enter a number between 0 and 255 cin gt gt u cout lt lt Here s the number in binary show_binary u 71 C A Beginner s Guide by Herbert Schildt cout lt lt Here s the complement of the number show_binary u return 0 Display the bits within a byte void show_binary unsigned int u int t For t 128 t gt 0 t t732 if u amp t cout lt lt 1 else cout lt lt Q cout lt lt n Here is a sample run produced by the program Enter a number between 0 and 255 9 Here s the number in binary 011 Here s the complement of the number 9 00011 10031311 0 0 In general amp and apply their operations directly to each bit in a value individually For this reason bitwise operations are not usually used in conditional statements the way the relational and logical operators are For example if x equals 7 then x amp amp 8 evaluates to true whereas x amp 8 evaluates to false CRITICAL SKILL 7 8 The Shift Operators The shift operators gt gt and lt lt move all bits in a variable to the right or left as specified The general form of the right shift operator is variable gt gt num bits and the left shift operator is variable lt lt num bits The
350. ince sameColor isa member of Cube it must be called on a Cube object which means that it can access the color variable of objects of type Cube directly Thus only objects of type Cylinder need to be passed to sameColor Progress Check 1 What is a friend function What keyword declares one 2 Isa friend function called on an object using the dot operator 3 Cana friend of one class be a member of another CRITICAL SKILL 9 7 Structures and Unions In addition to the keyword class C gives you two other ways to create a class type First you can create a structure Second you can create a union Each is examined here Structures Structures are inherited from the C language and are declared using the keyword struct A struct is syntactically similar to a class and both create a class type In the C language a struct can contain only data members but this limitation does not apply to C In C the struct is essentially just an alternative way to specify a class In fact in C the only difference between a class and a struct is that by default all members are public in a struct and private in a class In all other respects structures and classes are equivalent Here is an example of a structure 71 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std struct Test int get_i return i these are public void put_i int J i j by a private int i Struct
351. ing discussion you saw that it was possible to assign val the value of total indirectly through a pointer At this point you may have thought of this important question How does C know how many bytes to copy into val from the address pointed to by ptr Or more generally how does the compiler transfer the proper number of bytes for any assignment involving a pointer The answer is that the base type of the pointer determines the type of data upon which the pointer operates In this case because ptr is an int pointer four bytes of information are copied into val assuming a 32 bit int from the address pointed to by ptr However if ptr had been a double pointer for example then eight bytes would have been copied It is important to ensure that pointer variables always point to the correct type of data For example when you declare a pointer to be of type int the compiler assumes that anything it points to will be an integer variable If it doesn t point to an integer variable then trouble is usually not far behind For example the following fragment is incorrect int p double f p amp f ERROR This fragment is invalid because you cannot assign a double pointer to an integer pointer That is amp f generates a pointer to a double but p is a pointer to an int These two types are not compatible In fact the compiler would flag an error at this point and not compile your program Although two pointers must have compatible
352. inner s Guide by Herbert Schildt Member Access and Inheritance As you learned in Module 8 members of a class are often declared as private to prevent their unauthorized use or tampering Inheriting a class does not overrule the private access restriction Thus even though a derived class includes all of the members of its base class it cannot access those members of the base class that are private For example if width and height are made private in TwoDShape as shown here then Triangle will not be able to access them Access to private members is not granted to derived classes class TwoDShape these are now private double width width and height are now private double height public void showDim cout lt lt Width and height are lt lt width lt lt and lt lt height lt lt n Triangle is derived from TwoDShape class Triangle public TwoDShape public char style 20 double area return width height 2 Error Can t access e Can t access private members void showStyle of a base class cout lt lt Triangle is lt lt style lt lt n ti The Triangle class will not compile because the reference to width and height inside the area function causes an access violation Since width and height are now private they are accessible only by other members of their own class Derived classes have no access to them At
353. inside main n cout lt lt and return O This program displays the following output start Caught char inside Xhandler Caught char inside main End Progress Check 1 Show how to catch all exceptions 2 How do you specify the type of exceptions that can be thrown out of a function 3 How do you rethrow an exception Templates The template is one of C s most sophisticated and high powered features Although not part of the original specification for C it was added several years ago and is supported by all modern C compilers Templates help you achieve one of the most elusive goals in programming the creation of reusable code 13 C A Beginner s Guide by Herbert Schildt Using templates it is possible to create generic functions and classes In a generic function or class the type of data upon which the function or class operates is specified as a parameter Thus you can use one function or class with several different types of data without having to explicitly recode specific versions for each data type Both generic functions and generic classes are introduced here Ask the Expert Q It seems that there are two ways for a function to report an error to throw an exception or to return an error code In general when should I use each approach A You are correct there are two general approaches to reporting errors throwing exceptions and returning error codes Today language experts favor
354. int amp i i 10 this modifies calling argument Notice the declaration of i It is preceded by an amp which causes it to become a reference parameter This declaration is also used in the function s prototype Inside the function the following statement i 10 does not cause i to be given the value 10 Instead it causes the variable referenced by i in this case val to be assigned the value 10 Notice that this statement does not use the pointer operator When you 5 C A Beginner s Guide by Herbert Schildt use a reference parameter the C compiler automatically knows that it is an address and dereferences it for you In fact using the would be an error Since i has been declared as a reference parameter the compiler will automatically pass f the address of any argument it is called with Thus in main the statement Use reference parameters to create the swap function include lt iostream gt using namespace std Declare swap using reference parameters void swap int amp x int amp y int mair cout lt lt Initial values of i and j F cout lt lt i lt lt lt lt j lt lt n F Here the addresses of i and swap j i lt _ _ _AAA jjcre automatically passed to swap cout lt lt Swapped values of i and j cout lt lt i lt lt lt lt j lt lt n return 0 Here swap is defined as using call b
355. int amp i rather than the variable name like this int amp i Is there a difference A The short answer is no there is no difference between the two declarations For example here is another way to write the prototype to swap void swap int amp x int amp y As you can see the amp is immediately adjacent to int and not to x Furthermore some programmers also specify pointers by associating the with the type rather the variable as shown here float p These types of declarations reflect the desire by some programmers for C to contain a separate reference or pointer type However the trouble with associating the amp or with the type rather than the variable is that according to the formal C syntax neither the amp nor the is distributive over a list of variables and this can lead to confusing declarations For example the following declaration creates one not two int pointers int a b Here b is declared as an integer not an integer pointer because as specified by the C syntax when used in a declaration an or an amp is linked to the individual variable that it precedes not to the type that it follows It is important to understand that as far as the C compiler is concerned it doesn t matter whether you write int p or int p Thus if you prefer to associate the or amp with the type rather than the variable feel free to do so However to avoid confusion this book will conti
356. int running _avg int i static int sum 0 count 0 Because sum and count are static they will retain their values fan Gam e ia between calls to running_avg count 4 return sum count Here the local variables sum and count are both declared as static and initialized to 0 Remember for Static variables the initialization only occurs once not each time the function is entered The program uses running avg to compute and report the current average of the numbers entered by the user Because both sum and count are static they will maintain their values between calls causing the program to work properly To prove to yourself that the static modifier is necessary try removing it and running the program As you can see the program no longer works correctly because the running total is lost each time running avg returns static Global Variables When the static specifier is applied to a global variable it tells the compiler to create a global variable that is known only to the file in which the static global variable is declared This means that even though the variable is global other functions in other files have no knowledge of it and cannot alter its contents Thus it is not subject to side effects Therefore for the few situations where a local static variable cannot do the job you can create a small file that contains only the functions that need the global static variable separately compile that file and u
357. ion it will never return This is a very common error When developing programs with recursive functions use cout statements liberally so that you can watch what is going on and abort execution if you see that you have made a mistake Here is another example of a recursive function called reverse It prints its string argument backwards on the screen Print a string backwards using recursion include lt iostream gt using namespace std void reverse char s int main char str this is a test reverse str 34 C A Beginner s Guide by Herbert Schildt return OQ Print string backwards void reverse char s LE s reyverse s 1 else return cout lt lt s The reverse function first checks to see if it is passed a pointer to the null terminating the string If not then reverse calls itself with a pointer to the next character in the string When the null terminator is finally found the calls begin unraveling and the characters are displayed in reverse order One last point Recursion is often difficult for beginners Don t be discouraged if it seems a bit confusing right now Over time you will grow more accustomed to it The Quicksort In Module 4 you were shown a simple sorting method called the bubble sort QSDemo cpp It was mentioned at the time that substantially better sorts exist Here you will develop a version of one of the best the Quicksort The Quic
358. ion enhances compilation To use the Visual C command line compiler you must first execute the batch file VCVARS32 BAT which is provided by Visual C Visual Studio also provides a ready to use command prompt environment that can be activated by selecting Visual Studio Command Prompt from the list of tools shown under the Microsoft Visual Studio entry in the Start Programs menu of the taskbar The output from a C compiler is executable object code For a Windows environment the executable file will use the same name as the source file but have the exe extension Thus the executable version of Sample cpp will be in Sample exe Run the Program After a C program has been compiled it is ready to be run Since the output from a C compiler is executable object code to run the program simply enter its name at the command prompt For example to run Sample exe use this command line C gt Sample 11 C A Beginner s Guide by Herbert Schildt When run the program displays the following output C 1S power programming If you are using an Integrated Development Environment then you can run a program by selecting Run from a menu Consult the instructions for your specific compiler For the programs in this book it is usually easier to compile and run from the command line One last point The programs in this book are console based not window based That is they run ina Command Prompt session C is completely at h
359. irst a union cannot inherit a class Further a union cannot be a base class A union cannot have virtual member functions No static variables can be ch Fiaure 9 1 How i and ch of u var both share the same address members of a union A reference member cannot be used A union cannot have as a member any object that overloads the operator Finally no object can be a member of a union if the object has an explicit constructor or destructor Anonymous Unions There is a special type of union in C called an anonymous union An anonymous union does not include a type name and no variables of the union can be declared Instead an anonymous union tells the compiler that its member variables are to share the same location However the variables themselves are referred to directly without the normal dot operator syntax For example consider this program 25 C A Beginner s Guide by Herbert Schildt Demonstrate an anonymous union tinclude lt iostream gt ineclude lt cestring gt using namespace std int main define anonymous union union lt lt This is an anonymous union long l1 double d char s 4 7 now reference union elements directly 1 100000 cout lt lt 1 lt lt d 123 2342 The elements of an anonymous cout lt lt d lt lt union are referred to directly strcpy s hi P r cout lt lt s return As you can see the elements of the union ar
360. irtual function What is an abstract class Can an object of an abstract class be instantiated Explain how the pure virtual function helps implement the one interface multiple methods aspect of polymorphism 41 C A Beginner s Guide by Herbert Schildt Module 11 The C I O System Table of Contents CRITICAL SKILL 11 1 Understand I O streams CRITICAL SKILL 11 2 Know the I O class hierarchy CRITICAL SKILL 11 3 Overload the lt lt and gt gt operators CRITICAL SKILL 11 4 Format I O by using iso member functions CRITICAL SKILL 11 5 Format I O by using manipulators CRITICAL SKILL 11 6 Create your own manupulators CRITICAL SKILL 11 7 Open and close files CRITICAL SKILL 11 8 Read and write text files CRITICAL SKILL 11 9 Read and write binary files CRITICAL SKILL 11 10 Know additional file functions CRITICAL SKILL 11 11 Use randon access files I O CRITICAL SKILL 11 12 Check I O system status Since the beginning of this book you have been using the C I O system but you have been doing so without much formal explanation Since the I O system is based upon a hierarchy of classes it was not possible to present its theory and details without first discussing classes and inheritance Now it is time to examine the C I O system in detail The C I O system is quite large and it won t be possible to discuss here every class function or feature but this module will introduce you to the most important and commonl
361. is four elements long that contains the values 1 2 3 and 4 Because no explicit size is specified an array such as nums is called an unsized array Unsized arrays are quite useful For example imagine that you are using array initialization to build a table of Internet addresses as shown here char e1 16 www osborne com char e2 16 www weather com char e3 15 www amazon com As you might guess it is very tedious to manually count the characters in each address to determine the correct array dimension It is also error prone because it is possible to miscount and incorrectly size the array It is better to let the compiler size the arrays as shown here char e1 www osborne com char e2 www weather com char e3 www amazon com Besides being less tedious the unsized array initialization method allows you to change any of the strings without fear of accidentally forgetting to resize the array Unsized array initializations are not restricted to one dimensional arrays For a multidimensional array the leftmost dimension can be empty The other dimensions must be specified however so that the array can be properly indexed Using unsized array initializations you can build tables of varying lengths with the compiler automatically allocating enough storage for them For example here sars is declared as an unsized array 20 C A Beginner s Guide by Herbert Schildt int sqrs 2 1 1 2 4 3 9
362. is is a test printin x L 23 23 printin printin printin 99 1 Here are some values alse ya aa gt QOOOOOL Y3 100 01 print print Fh print print print print H print print a eT SESS gt gt a eT oO printin Done return 0 Here are the println functions void printin bool b if b cout lt lt true n else cout lt lt false n void println int i cout lt lt 1 lt lt n void printlin long i cout lt lt 1 lt lt n void printlin char ch cout lt lt ch lt lt n void printin char str cout lt lt str lt lt n pe 24 c A Beginner s Guide by Herbert Schildt void printin double d cout lt lt d lt lt n Here are the print functions void print bool b i1f b cout lt lt true else cout lt lt false void print int i cout lt lt i void print long i cout lt lt i void print char ch cout lt lt ch void print char str cout lt lt str void print double qd cout lt lt d The output from the program is shown here true 10 This is a test x 99 123 23 Here are some values false 88 100000 100 01 Done 25 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 6 8 Default Function Arguments The next function related feature to be discus
363. is module discusses the statements that control a program s flow of execution There are three categories of selection statements which include the if and the switch iteration statements which include the for while and do while loops and jump statements which include break continue return and goto Except for return which is discussed later in this book the remaining control statements including the if and for statements to which you have already had a brief introduction are examined here 1 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 3 1 The if Statement Module 1 introduced the if statement Now it is time to examine it in detail The complete form of the if Statement is ift expression statement else statement where the targets of the if and else are single statements The else clause is optional The targets of both the if and else can also be blocks of statements The general form of the if using blocks of statements is if expression statement sequence else statement seguence If the conditional expression is true the target of the if will be executed otherwise the target of the else if it exists will be executed At no time will both be executed The conditional expression controlling the if may be any type of valid C expression that produces a true or false result The following program demonstrates the if by playing a simple version of the guess the magic number game
364. isplay a file from a given starting point include lt iostream gt include lt fstream gt include lt cstdlib gt using namespace std int main int argc char argv char chy i1f arge 3 cout lt lt Usage NAME lt filename gt lt starting location gt n return 1 ifstream in argv 1 los in ios binary if in cout lt lt Cannot open file n return 1 in seekg atoi argv 2 los beg lt This moves the get pointer while in get ch cout lt lt ch return 0 You can determine the current position of each file pointer using these functions pos_type tellg pos type tellp Here pos_ type is a type defined by ios that is capable of holding the largest value that either function can return There are overloaded versions of seekg and seekp that move the file pointers to the location specified by the return values of tellg and tellp Their prototypes are shown here istream amp seekg pos_ type position ostream amp seekp pos_ type position Progress Check 1 What function detects the end of the file 2 What does getline do 3 What functions handle random access position requests CRITICAL SKILL 11 12 Checking I O Status 37 C A Beginner s Guide by Herbert Schildt The C I O system maintains status information about the outcome of each I O operation The current status of an I O stream is described in an object of type iosta
365. isuse could easily cause extensive damage to a program Do you have any tips on avoiding pointer errors A First make sure that pointer variables are initialized before using them That is make sure that a pointer actually points to something before you attempt to use it Second make sure that the type of the object to which a pointer points is the same as the base type of pointer Third don t perform operations through null pointers Recall that a null pointer indicates that the pointer points nowhere Finally don t cast pointers just to make your code compile Usually pointer mismatch errors indicate that you are thinking about something incorrectly Casting one type of pointer into another is usually needed only in unusual circumstances Here p is declared as a pointer to an integer and q as a pointer to a pointer to an integer The cout statement will print the number 10 on the screen 41 C A Beginner s Guide by Herbert Schildt Module 4 Mastery Check 1 Show how to declare a short int array called hightemps that is 31 elements long 2 In C all arrays begin indexing at 3 Write a program that searches an array of ten integers for duplicate values Have the program display each duplicate found 4 What is a null terminated string 5 Write a program that prompts the user for two strings and then compares the strings for equality but ignores case differences Thus ok and OK will compare as equal
366. it really isn t because you can easily create a left and right rotate by using the other bitwise operators This project creates two functions rrotate and lrotate which rotate a byte in the right or left direction Each function takes two parameters The first is the value to be rotated The second is the number of places to rotate Each function returns the result This project involves several bit manipulations and shows the bitwise operators in action Step by Step 1 Create a file called rotate cpp 2 Add the lrotate function shown here It performs a left rotate Lett rotate a byte n places unsigned char lrotate unsigned char val int n t unsigned int t t val for int i 0 i lt n i t t lt lt 1 If a bit shifts out it will be in bit 8 amp 8 of the integer t If this is the case put that bit on the right side 1f t amp 256 t t 1 put a 1 on the right end return t return the lower 8 bits Here is how lrotate works The function is passed the value to rotate in val and the number of places to rotate is passed in n The function assigns val to t which is an unsigned int Transferring the value to an unsigned int is necessary because it allows bits shifted off the left side to be recovered Here s why Because an unsigned int is larger than a byte when a bit is shifted off the left side of a byte value it simply moves to bit 8 of the integer value The va
367. ith delete is undefined and will almost certainly cause serious problems such as a system crash 23 C A Beginner s Guide by Herbert Schildt Initializing Allocated Memory You can initialize allocated memory to some known value by putting an initializer after the type name in the new statement Here is the general form of new when an initialization is included p var new var_type initializer Of course the type of the initializer must be compatible with the type of data for which memory is being allocated Ask the Expert Q have seen some C code that uses the functions malloc and free to handle dynamic allocation What are these functions A The C language does not support the new and delete operators Instead C uses the functions malloc and free for dynamic allocation malloc allocates memory and free releases it C also supports these functions and you will sometimes see malloc and free used in C code This is especially true if that code has been updated from older C code However you should use new and delete in your code Not only do new and delete offer a more convenient method of handling dynamic allocation but they also prevent several types of errors that are common when working with malloc and free One other point Although there is no formal rule that states this it is best not to mix new and delete with malloc and free in the same program There is no guarantee that th
368. itialization Although the preceding examples have used only constants as initializers C allows variables to be initialized dynamically using any expression valid at the time the variable is declared For example here is a short program that computes the volume of a cylinder given the radius of its base and its height 16 C A Beginner s Guide by Herbert Schildt if Demonstrate dynamic initialization inelude lt iostream gt using namespace sted int maini double radius 4 0 height 5 0 ff dynamically initialize volume double wolume 3 1416 radius radius height volume is dynamically cout lt lt Volume is lt lt volume initialized at runtime return Here three local variables radius height and volume are declared The first two radius and height are initialized by constants However volume is initialized dynamically to the volume of the cylinder The key point here is that the initialization expression can use any element valid at the time of the initialization including calls to functions other variables or literals Operators C provides a rich operator environment An operator is a symbol that tells the compiler to perform a specific mathematical or logical manipulation C has four general classes of operators arithmetic bitwise relational and logical C also has several additional operators that handle certain special situations This chapter will examine the arithmetic r
369. ksort invented and named by C A R Hoare is the best general purpose sorting algorithm currently available The reason it could not be shown in Module 4 is that the best implementations of the Quicksort rely on recursion The version we will develop sorts a character array but the logic can be adapted to sort any type of object The Quicksort is built on the idea of partitions The general procedure is to select a value called the comparand and then to partition the array into two sections All elements greater than or equal to the comparand are put on one side and those less than the value are put on the other This process is then repeated for each remaining section until the array is sorted For example given the array fedacb and using the value d as the comparand the first pass of the Quicksort would rearrange the array as follows This process is then repeated for each section that is bca and def As you can see the process is essentially recursive in nature and indeed the cleanest implementation of Quicksort is as a recursive function You can select the comparand value in two ways You can either choose it at random or you can select it by averaging a small set of values taken from the array For optimal sorting you should select a value that is precisely in the middle of the range of values However this is not easy to do for most sets of data In the worst case the value chosen is at one extremity 35 C A Beginner s Gui
370. ld it be used in C programs A The answer to the first question is yes The C I O system is available to C programmers The answer to the second question is a qualified no The C I O system is not object oriented Thus you will nearly always find the C I O system more compatible with C programs However the C I O system is still widely used and is quite streamlined carrying little overhead Thus for some highly specialized programs the C I O system might be a good choice Information on the C I O system can be found in my book C The Complete Reference Osborne McGraw Hill 24 C A Beginner s Guide by Herbert Schildt Progress Check 1 What class creates an input file 2 What function opens a file 3 Can you read and write to a file using lt lt and gt gt CRITICAL SKILL 11 9 Unformatted and Binary I O While reading and writing formatted text files is very easy it is not always the most efficient way to handle files Also there will be times when you need to store unformatted raw binary data not text The functions that allow you to do this are described here When performing binary operations on a file be sure to open it using the ios binary mode specifier Although the unformatted file functions will work on files opened for text mode some character translations may occur Character translations negate the purpose of binary file operations In general there are two ways to write and read unformatted
371. ldt int main int i j 1 10 j 20 cout lt lt Initial values of i and j cout lt lt i lt lt lt lt j lt lt n eswap amp J amp 1 call swap with addresses of i and j on ee Call swap with the ope ene Vee es ee es vddreccct of the variables you want to exchange cout lt lt i lt lt lt lt j lt lt n return OQ In main the variable i is assigned the value 10 and j the value 20 Then swap is called with the addresses of i and j The unary operator amp is used to produce the addresses of the variables Therefore the addresses of i and j not their values are passed into swap When swap returns i and j will have their values exchanged as the following output shows Initial values of i and j 10 20 Swapped values of i and j 20 10 Progress Check 1 Explain call by value 2 Explain call by reference 3 What parameter passing mechanism does C use by default CRITICAL SKILL 6 4 Reference Parameters While it is possible to achieve a call by reference manually by using the pointer operators this approach is rather clumsy First it compels you to perform all operations through pointers Second it requires that you remember to pass the addresses rather than the values of the arguments when calling the function Fortunately in C it is possible to tell the compiler to automatically use call by reference rather than call by value for
372. le define GETFILE Enter File Name pe gout lt lt GETFILE is a macro name n will not print Enter File Name is a macro name but rather will print GETFILE is a macro name If the string is longer than one line you can continue it on the next by placing a backslash at the end of the line as shown in this example define LONG_STRING this is a very long string that is used as an example It is common practice among C programmers to use capital letters for macro names This convention helps anyone reading the program know at a glance that a macro substitution will take place Also it is best to put all defines at the start of the file or perhaps in a separate include file rather than sprinkling them throughout the program One last point C provides a better way of defining constants than by using define This is to use the const specifier However many C programmers migrated from C where define is commonly used for this purpose Thus you will likely see it frequently in C code too Function Like Macros The define directive has another feature The macro name can have arguments Each time the macro name is encountered the arguments associated with it are replaced by the actual arguments found in the program This creates a function like macro Here is an example 2 C A Beginner s Guide by Herbert Schildt Use a function like macro include lt iostream gt using namespace std define MIN
373. le the following checks if mystream is currently open if mystream is open cout lt lt File is not open n I Although it is entirely proper to use the open function for opening a file most of the time you will not do so because the ifstream ofstream and fstream classes have constructors that automatically open the file The constructors have the same parameters and defaults as the open function Therefore the most common way you will see a file opened is shown in this example ifstream mystream myfile open file for input If for some reason the file cannot be opened the value of the associated stream variable will evaluate to false To close a file use the member function close For example to close the file linked to a stream called mystream you would use this statement mystream close The close function takes no parameters and returns no value 22 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 11 8 Reading and Writing Text Files The easiest way to read from or write to a text file is to use the lt lt and gt gt operators For example this program writes an integer a floating point value and a string to a file called test Write to file include lt iostream gt include lt fstream gt using namespace std int main ofstream out test Create and open a file called S61 cue 1 test for text output cout lt lt Cannot open file n
374. les For example if you try to access either sum or count from the first file you will receive an error message To review The name of a local static variable is known only to the function or block of code in which it is declared and the name of a global static variable is known only to the file in which it resides In essence the static modifier allows variables to exist that are known to the scopes that need them thereby controlling and limiting the possibility of side effects Variables of type static enable you the programmer to hide portions of your program from other portions This can be a tremendous advantage when you are trying to manage a very large and complex program Ask the Expert Q have heard that some C programmers do not use static global variables Is this true A Although static global variables are still valid and widely used in C code the C Standard discourages their use Instead it recommends another method of controlling access to global variables that involves the use of namespaces which are described later in this book However static global variables are widely used by C programmers because C does not support namespaces For this reason you will continue to see static global variables for a long time to come CRITICAL SKILL 7 4 register Variables Perhaps the most frequently used storage class specifier is register The register modifier tells the compiler to store a variable in such a way that it
375. les or functions defined after the public specifier are accessible by other parts of your program Typically your program will access the private members of a class through its public functions Notice that the public keyword is followed by a colon Although there is no syntactic rule that enforces it a well designed class should define one and only one logical entity For example a class that stores names and telephone numbers will not normally also store information about the stock market average rainfall sunspot cycles or other unrelated information The point here is that a well designed class groups logically connected information Putting unrelated information into the same class will quickly destructure your code Let s review In C a class creates a new data type that can be used to create objects Specifically a class creates a logical framework that defines a relationship between its members When you declare a variable of a class you are creating an object An object has physical existence and is a specific instance of a class That is an object occupies memory space but a type definition does not CRITICAL SKILL 8 2 Defining a Class and Creating Objects To illustrate classes we will be evolving a class that encapsulates information about vehicles such as cars vans and trucks This class is called Vehicle and it will store three items of information about a vehicle the number of passengers that it can carry its fuel c
376. literal For example is k the same as k A No You must not confuse strings with characters A character literal represents a single letter of type char A string containing only one letter is still a string Although strings consist of characters they are not the same type 14 C A Beginner s Guide by Herbert Schildt The following sample program illustrates a few of the escape sequences Demonstrate some escape sequences include lt Lostream gt using namespace sted int maint i cout lt lt one ttwoitthreen cout lt lt 123 b b45 The bib will backspace over the 2 and 3 return OU The output 1s shown here one twa three 145 Here the first cout statement uses tabs to position the words two and three The second cout statement displays the characters 123 Next two backspace characters are output which deletes the 2 and 3 Finally the characters 4 and 5 are displayed 0 Progress Check 1 By default what is the type of the literal 10 What is the type of the literal 10 0 2 How do you specify 100 as a long int How do you specify 100 as an unsigned int 3 What is b Answer Key 1 10is anint and 10 0 is a double 2 100 asa long int is 100L 100 as an unsigned int is 100U 3 bis the escape sequence that causes a backspace CRITICAL SKILL 2 3 A Closer Look at Variables Variables were introduced in Module 1 Here we
377. ll arrays have zero as the index of their first element Because sample has ten elements it has index values of O through 9 You access an array element by indexing the array using the number of the element To index an array specify the number of the element you want surrounded by square brackets Thus the first element in sample is sample 0 and the last element is sample 9 For example the following program loads sample with the numbers 0 through 9 tinclude lt iostream gt using namespace std int main int sample 10 this reserves 10 integer elements int t load the array for t 0 t lt 10 t sample t t I deactes the areas Notice how sample is indexed for t 0 t lt 10 t cout lt lt This is sample lt lt t lt lt lt lt sgample t lt lt n return 0 The output from this example is shown here This is sample 0O 0 2 C A Beginner s Guide by Herbert Schildt This is sample 1 This is sample 2 This is sample 3 This is sample 4 This is sample 5 This is sample o This is sample 7 This is sample 8 This is sample 9 Oo OATS OP WN FEF In C all arrays consist of contiguous memory locations That is all array elements reside next to each other in memory The lowest address corresponds to the first element and the highest address corresponds to the last element For example after this fragment is run int nums 5 int i for i 0 i lt 5 i nums i
378. ll be lost when going from an integer to a short integer When converting from a floating point type to an integer the fractional part will be lost If the target type is not large enough to store the result then a garbage value will result 26 C A Beginner s Guide by Herbert Schildt A word of caution Although C automatically converts any built in type into another the results won t always be what you want Be careful when mixing types in an expression Expressions Operators variables and literals are constituents of expressions You might already know the general form of an expression from other programming experience or from algebra However a few aspects of expressions will be discussed now CRITICAL SKILL 2 9 Type Conversion in Expressions When constants and variables of different types are mixed in an expression they are converted to the same type First all char and short int values are automatically elevated to int This process is called integral promotion Next all operands are converted up to the type of the largest operand which is called type promotion The promotion is done on an operation byoperation basis For example if one operand is an int and the other a long int then the int is promoted to long int Or if either operand is a double the other operand is promoted to double This means that conversions such as that from a char to a double are perfectly valid Once a conversion has been applied each p
379. lled followed by that of B The results of the foregoing experiment can be generalized as follows When an object of a derived class is created the base class constructor is called first followed by the constructor for the derived class When a derived object is destroyed its destructor is called first followed by that of the base class Put differently constructors are executed in the order of their derivation Destructors are executed in reverse order of derivation In the case of a multilevel class hierarchy that is where a derived class becomes the base class for another derived class the same general rule applies Constructors are called 26 C A Beginner s Guide by Herbert Schildt in order of derivation destructors are called in reverse order When a class inherits more than one base class at a time constructors are called in order from left to right as specified in the derived class inheritance list Destructors are called in reverse order right to left Progress Check 1 Cana derived class be used as a base class for another derived class 2 Ina class hierarchy in what order are the constructors called 3 Ina class hierarchy in what order are the destructors called Ask the Expert Q Why are constructors called in order of derivation and destructors called in reverse order A If you think about it it makes sense that constructors are executed in order of derivation Because a base class has no knowledge of any
380. loc return qi getloc Demonstrate the generic Queue int main Queue lt int gt 10a 10 1iQ0b 10 create two integer queues 1Qa put 1 1Qa put 2 1Q0a put 3 iQb put 10 iQb put 20 iQb put 30 cout lt lt Contents of integer queue 10a for int 1 0 1 lt 3 1 4 cout lt lt i0a get lt lt C A Beginner s Guide by Herbert Schildt cout lt lt endl cout lt lt Contents of integer queue iQb for int i 0 i lt 3 i cout lt lt i0b get lt lt cout lt lt endl Queue lt double gt dQa 10 dOb 10 create two double queues Queue lt double gt dQa 10 dQb 10 create two double queues dQa put 1 01 dQa put 2 02 dQa put 3 03 dQb put 10 01 dQb put 20 02 dQb put 30 03 cout lt lt Contents of double queue dQa for int 1i 0 1 lt 3 1 cout lt lt dQa get lt lt cout lt lt endl cout lt lt Contents of double queue dQb for int i 0 1 lt 3 i cout lt lt dQb get lt lt T cout lt lt endl return QO The output is shown here Contents of integer queue i0a 1 2 3 Contents of integer queue i0b 10 20 30 Contents of double queue dQa 1 01 2 02 3 03 Contents of double queue dQOb 10 01 20 02 30 03 7 As the Queue class illustrates generic functions and classes are powerful tools that you can use to maximize your programming efforts because they allow you to define
381. loop When in reaches the end of the file it will be false causing the while loop to stop There is actually a more compact way to code the loop that reads and displays a file as shown here while in get ch cout lt lt ch This form works because get returns the stream in and in will be false when the end of the file is encountered This program uses put to write a string to a file 26 C A Beginner s Guide by Herbert Schildt Use put to write to a file tinclude lt iostream gt include lt fstream gt using namespace std int main char p hello there n ofstream out test ios out 1os binary 1f out f cout lt lt Cannot open file n return 1 ii Write characters until the null terminator is reached while p e out close Write a string to a file using put No character translations will occur return 0 After this program executes the file test will contain the string hello there followed by a newline character No character translations will have taken place Reading and Writing Blocks of Data To read and write blocks of binary data use the read and write member functions Their prototypes are shown here istream amp read char buf streamsize num ostream amp write const char buf streamsize num The read function reads num bytes from the associated stream and puts them in the buffer pointed to by buf The write functio
382. loop keeps running The 23 C A Beginner s Guide by Herbert Schildt increment is an expression that determines how the loop control variable is incremented each time the loop repeats The following program demonstrates the for It prints the numbers 1 through 100 on the screen if A program that illustrates the for loop tinelude lt Lostream gt using namespace std int main T This is a for loop int count for count 1 count lt 100 count count 1 cout lt lt count lt lt m return OU In the loop count is initialized to 1 Each time the loop repeats the condition count lt 100 is tested If itis true the value is output and count is increased by one When count reaches a value greater than 100 the condition becomes false and the loop stops running In professionally written C code you will almost never see a statement like count counttl because C includes a special increment operator that performs this operation more efficiently The increment operator is two consecutive plus signs The operator increases its operand by 1 For example the preceding for statement will generally be written like this for count l count lt 100 count cout lt lt count lt lt T T This is the form that will be used throughout the rest of this book C also provides a decrement operator which is specified as It decreases its operand by 1 Progress Check 1 What does the if
383. lt n return stream return the stream Let s look closely at this function because many of its features are common to all inserter functions First notice that it is declared as returning a reference to an object of type ostream This declaration is necessary so that several inserters of this type can be combined in a compound I O expression Next the function has two parameters The first is the reference to the stream that occurs on the left side of the lt lt operator The second parameter is the object that occurs on the right side This parameter can also be a reference to the object if you like Inside the function the three values contained in an object of type ThreeD are output and stream is returned Here is a short program that demonstrates the inserter 5 C A Beginner s Guide by Herbert Schildt Demonstrate a custom inserter include lt iostream gt using namespace std class ThreeD public int x Y Z 3 D coordinates ThreeD int a int b int c x a y b z C F Display X Y Z coordinates ThreeD inserter ostream amp operator lt lt ostream amp stream ThreeD obj An inserter for Three D stream lt lt obj x lt lt stream lt lt obj y lt lt stream lt lt obj z lt lt yn return stream return the stream int main ThreeD a l 2 3 b 3 4 5 c 5 6 TF cout lt lt a lt lt b lt lt c
384. lude lt iostream gt include lt fstream gt using namespace std int main int argc char argv register int i unsigned char buf1 1024 buf2 1024 33 C A Beginner s Guide by Herbert Schildt 1f arge 3 cout lt lt Usage compfiles lt filel gt lt file2 gt n return 1 1fstream fl argv l l1os in 1os binary 1f f1 cout lt lt Cannot open first file n return 1 1fstream f2 argv 2 108 in 10os binary 1E 2 cout lt lt Cannot open second file n return 1 cout lt lt Comparing files n do fl read char bufl sizeof bufl f2 read char buf2 sizeof buf2 1f fl gcount 2 gcount f cout lt lt Files are of differing sizes n Cl close f2 close return r compare contents of buffers For 1 0 i lt fl gcount i 1f bufl i buf2 i f cout lt lt Files differ n fil close f2 close return OQ while fl eof amp amp 2 e0f cout lt lt Files are the same n fi close f2 close return O 34 C A Beginner s Guide by Herbert Schildt 7 To try Compiles first copy CompFiles cpp to a file called temp txt Then try this command line CompFiles CompFiles temp txt The program will report that the files are the same Next compare CompFiles cpp to a different file such as one of the other program files from this module You will see that CompFiles reports that the files dif
385. lue x increment x y and z y f Zt 4 f return temp return original value Show X Y Z coordinates void ThreeD show cout lt lt x lt lt cout lt lt y lt lt cout lt lt z lt lt n 35 C A Beginner s Guide by Herbert Schildt int main ThreeD a 1 2 3 ThreeD b cout lt lt Original value of a a show cout lt lt n a m cout lt lt Value after a a show a n cout lt lt Value after at a show cout lt lt nn prefix increment Calls prefix increment function postfix increment Calls postfix increment function b a b receives a s value after increment cout lt lt Value of a after b a show cout lt lt Value of b after b b show cout lt lt n b a b receives a s value prior cout lt lt Value of a after b a show cout lt lt Value of b after b b show return 0 The output from the program is shown here Original value of a 1 2 3 Value after ta 2 3 4 Value after att 3 4 5 Value of a after b tta 4 5 6 Value of b after b tta 4 5 6 Value of a after b att 5 6 7 Value of b after b att 4 5 6 36 A a a to increment C A Beginner s Guide by Herbert Schildt Remember that if the precedes its operand the operator is called
386. lue of this bit can then be copied into bit O of the byte value thus performing a rotation The actual rotation is performed as follows A loop is established that performs the required number of rotations one at atime Inside the loop the value of t is left shifted one place This causes a O to be 25 C A Beginner s Guide by Herbert Schildt brought in on the right However if the value of bit 8 of the result which is the bit shifted out of the byte value is a 1 then bit 0 is set to 1 Otherwise bit O remains 0O The eighth bit is tested using the statement if t amp 256 The value 256 is the decimal value in which only bit 8 is set Thus t amp 256 will be true only when t has the value 1 in bit 8 After the rotation has been completed t is returned Since lrotate is declared to return an unsigned char value only the lower 8 bits of t are returned 3 Add the rrotate function shown next It performs a right rotate Right rotate a byte n places unsigned char rrotate unsigned char val int n unsigned int t t val First move the value 8 bits higher t t lt lt B for int i 0O i lt n i t t gt gt 1 Tf a bit shifts out it will be in bit 7 of the integer t If this is the case put that bit on the left side 1f t amp 128 t 32768 put a 1 on left end Finally move the result back to the lower 8 bits of t t t gt gt return t Th
387. lues can have with one another and logical refers to the ways in which true and false values can be connected together Since the relational operators produce true or false results they often work with the logical operators For this reason they will be discussed together here The relational and logical operators are shown in Table 2 4 Notice that in C not equal to is represented by and equal to is represented by the double equal sign In C the outcome of a relational or logical expression produces a bool result That is the outcome of a relational or logical expression is either true or false NOTE For older compilers the outcome of a relational or logical expression will be an integer value of either O or 1 This difference is mostly academic though because C automatically converts true into 1 and false into O and vice versa as explained earlier The operands for a relational operator can be of nearly any type as long as they can be meaningfully compared The operands to the logical operators must produce a true or false result Since any nonzero value is true and zero is false this means that the logical operators can be used with any expression that evaluates to a zero or nonzero result Thus any expression other than one that has a void result can be used 20 C A Beginner s Guide by Herbert Schildt Relational Operators Operator Meaning gt Greater than gt Greater than or equal to lt Less than lt L
388. ly separate from the data contained in sportscar Figure 8 1 depicts this situation 5 C A Beginner s Guide by Herbert Schildt passengers Figure 8 1 One object s instance variables are separate from another s med Progress Check 1 A class can contain what two things 2 What operator is used to access the members of a class through an object 3 Each object has its own copies of the class CRITICAL SKILL 8 3 Adding Member Functions to a Class So far Vehicle contains only data but no functions Although data only classes are perfectly valid most classes will have function members In general member functions manipulate the data defined by the class and in many cases provide access to that data Typically other parts of your program will interact with a class through its functions To illustrate member functions we will add one to the Vehicle class Recall that main in the preceding examples computed the range of a vehicle by multiplying its fuel consumption rate by its fuel capacity While technically correct this is not the best way to handle this computation The calculation of a vehicle s range is something that is best handled by the Vehicle class itself The reason for this conclusion is easy to understand The range of a vehicle is dependent upon the capacity of the fuel tank and the rate of fuel consumption and both of these quantities are encapsulated by Vehicle By adding a functio
389. machine code 5 C A Beginner s Guide by Herbert Schildt that is directly executed by the CPU Thus it is tied to a specific CPU and operating system If you want to run a C program on a different system you need to recompile it into machine code specifically targeted for that environment To create a C program that would run in a variety of environments several different executable versions of the program are needed Java and C achieve portability by compiling a program into a pseudocode intermediate language In the case of Java this intermediate language is called bytecode For C it is called Microsoft Intermediate Language MSIL In both cases this pseudocode is executed by a runtime system For Java this runtime system is called the Java Virtual Machine JVM For C it is the Common Language Runtime CLR Therefore a Java program can run in any environment for which a JVM is available and a C program can run in any environment in which the CLR is implemented Since the Java and C runtime systems stand between a program and the CPU Java and C programs incur an overhead that is not present in the execution of a C program This is why C programs usually run faster than the equivalent programs written in Java or C Java and C were developed in response to the unique programming needs of the online environment of the Internet C was also designed to simplify the creation of software components The Internet is
390. matically creates three versions of swapargs one that will exchange integer values one that will exchange floating point values and one that will swap 15 C A Beginner s Guide by Herbert Schildt characters Thus the same generic swap function can be used to exchange arguments of any type of data Here are some important terms related to templates First a generic function that is a function definition preceded by a template statement is also called a template function Both terms are used interchangeably in this book When the compiler creates a specific version of this function it is said to have created a specialization This is also called a generated function The act of generating a function is referred to as instantiating it Put differently a generated function is a specific instance of a template function A Function with Two Generic Types You can define more than one generic data type in the template statement by using a comma separated list For example this program creates a template function that has two generic types include lt iostream gt using namespace std template lt class Typel class Type2 gt Two generic types void myfunc Typel x Type2 y cout lt lt x lt lt lt lt y lt lt n int maini myfunc 10 hi myfune 0 23 10L return 0 In this example the placeholder types Type1 and Type2 are replaced by the compiler with the data types int and char and double
391. member function called gcount which has this prototype streamsize gcount gcount returns the number of characters read by the last input operation 23 C A Beginner s Guide by Herbert Schildt Progress Check 1 To read or write binary data you open a file using what mode specifier 2 What does get do What does put do 3 What function reads a block of data CRITICAL SKILL 11 10 More I O Functions The C I O system defines other I O related functions several of which you will find useful They are discussed here More Versions of get In addition to the form shown earlier the get function is overloaded in several different ways The prototypes for the three most commonly used overloaded forms are shown here istream amp get char buf streamsize num istream amp get char buf streamsize num char delim int get The first form reads characters into the array pointed to by buf until either num 1 characters have been read a newline is found or the end of the file has been encountered The array pointed to by buf will be null terminated by get If the newline character is encountered in the input stream it is not extracted Instead it remains in the stream until the next input operation The second form reads characters into the array pointed to by buf until either num 1 characters have been read the character specified by delim has been found or the end of the file has been en
392. mensional objects class TwoDShape these are private double width double height add a name field char name 20 public Default constructor TwobDshape width height 0 0 strepy name unknown Constructor for TwoDShape TwobShape double w double h char n width w height h strepy name n f Construct object with equal width and height TwobShape double x char n width height x strepy name mn 34 C A Beginner s Guide by Herbert Schildt void showDim cout lt lt Width and height are lt lt width lt lt and lt lt height lt lt n accessor functions double getWidth return width double getHeight return height void setWidth double w width w void setHeight double h height h char getName return name Add area to TwoDShape and make it virtual virtual double area The area function is cout lt lt Error area must be overridden n now virtual return 0 0 Triangle is derived from TwoDShape class Triangle public TwoDShape char style 20 now private public A default constructor This automatically invokes the default constructor of TwoDShape Triangle strepy style unknown Constructor with three parameters Triangle char str double w double h TwoDShape w h triangle strepy style str Construct an isosc
393. ment include lt iostream gt include lt cstdlib gt 4 C A Beginner s Guide by Herbert Schildt using namespace std int main int magic magic number int guess user s guess magic rand get a random number cout lt lt Enter your guess cin gt gt guess if guess magic cout lt lt Right n cout lt lt magic lt lt is the magic number n else cout lt lt Sorry you re wrong if guess gt magic cout lt lt Your guess is too high n else cout lt lt Your guess is too low n Here a nested if provides return 0 feedback to the player The if else if Ladder A common programming construct that is based upon nested ifs is the if else if ladder also referred to as the if else if staircase It looks like this it condition statement else if condition statement else 1f condition statement else statement The conditional expressions are evaluated from the top downward As soon as a true condition is found the statement associated with it is executed and the rest of the ladder is bypassed If none of the conditions is true then the final else statement will be executed The final else often acts as a default condition that is if all other conditional tests fail then the last else statement is performed If there is no final else and all other conditions are false then no action will take place The following program demo
394. ment in the str array That is after the assignment p1 will point to str O Here s why In C using the name of an array without an index generates a pointer to the first element in the array Thus the assignment 29 C A Beginner s Guide by Herbert Schildt pil str assigns the address of str O to p1 This is a crucial point to understand When an unindexed array name is used in an expression it yields a pointer to the first element in the array Since after the assignment p1 points to the beginning of str you can use p1 to access elements in the array For example if you want to access the fifth element in str you can use str 4 or p1 4 Both statements obtain the fifth element Remember array indices start at zero so when str is indexed a 4 is used to access the fifth element A 4 is also added to the pointer p1 to get the fifth element because p1 currently points to the first element of str The parentheses surrounding p1 4 are necessary because the operation has a higher priority than the operation Without them the expression would first find the value pointed to by p1 the first location in the array and then add 4 to it In effect C allows two methods of accessing array elements pointer arithmetic and array indexing This is important because pointer arithmetic can sometimes be faster than array indexing especially when you are accessing an array in strictly sequential order Since speed is often
395. meters are essentially variables that receive the value of the arguments passed to the function when it is called If the function has no parameters then the parameter list will be empty Braces surround the body of the function The function body is composed of the C statements that define what the function does The function terminates and returns to the calling code when the closing curly brace is reached CRITICAL SKILL 5 2 Creating a Function It is easy to create a function Since all functions share the same general form they are all similar in structure to the main functions that you have been using Let s begin with a simple example that contains two functions main and myfunc Before running this program or reading the description that follows examine it closely and try to figure out exactly what it displays on the screen This program contains two functions main and myfunc include lt iostream gt using namespace std void myfunc myfunc s prototype lt This is the prototype for myfune int main cout lt lt In main n myfune call myfunc cout lt lt Back in main n return C This is the function s definition void myfune cout lt lt Inside myfunc n 2 C A Beginner s Guide by Herbert Schildt This is the function called myfunc The program works like this First main begins and it executes the first cout sta
396. mp D1_obj p 2who access Dl s who p amp D2_obj p gt who access B s who because This calls the whof defined by B D2 does not redefine it return OQ The program now outputs the following 32 C A Beginner s Guide by Herbert Schildt Base First derivation Base Because D2 does not override who the version of who defined in B is used instead Keep in mind that inherited characteristics of virtual are hierarchical Therefore if the preceding example is changed such that D2 is derived from D1 instead of B then when who is called on an object of type D2 it will not be the who inside B but the version of who declared inside D1 that is called since it is the class closest to D2 Why Virtual Functions As stated earlier virtual functions in combination with derived types allow C to support runtime polymorphism Polymorphism is essential to object oriented programming because it allows a generalized class to specify those functions that will be common to all derivatives of that class while allowing a derived class to define the specific implementation of some or all of those functions Sometimes this idea is expressed as follows the base class dictates the general interface that any object derived from that class will have but lets the derived class define the actual method used to implement that interface This is why the phrase one interface multiple methods is often
397. mpiler that only one copy of that variable will exist and that all objects of the class will share that variable Unlike regular data members individual copies of a static member variable are not made for each object No matter how many objects of a class are created only one copy of a static data member exists Thus all objects of that class use that same variable All static variables are initialized to zero if no other initialization is specified When you declare a static data member within a class you are not defining it Instead you must provide a global definition for it elsewhere outside the class This is done by redeclaring the static variable using the scope resolution operator to identify which class it belongs to This causes storage to be allocated for the static variable Here is an example that uses a static member Use a static instance variable tinclude lt iostream gt using namespace std Declare a static data member It will be class ShareVar shared by all instances of ShareVar static int num public void setnum int i num i void shownum cout lt lt num lt lt i int ShareVar num define num Define the static data member int main shareVar a Bb a shownum prints 0 b shownum prints 0 a setnum 10 set static num to 10 42 C A Beginner s Guide by Herbert Schildt a shownum prints 10 b shownum also prints 10 return
398. msize num istream amp getline char buf streamsize num char delim The first form reads characters into the array pointed to by buf until either num 1 characters have been read a newline character has been found or the end of the file has been encountered The array pointed to by buf will be null terminated by getline If the newline character is encountered in the input stream it is extracted but is not put into buf The second form reads characters into the array pointed to by buf until either num 1 characters have been read the character specified by delim has been found or the end of the file has been encountered The array pointed to by buf will be null terminated by getline If the delimiter character is encountered in the input stream it is extracted but is not put into buf As you can see the two versions of getline are virtually identical to the get buf num and get buf num delim versions of get Both read characters from input and put them into the array pointed to by buf until either num 1 characters have been read or until the delimiter character is encountered The difference between get and getline is that getline reads and removes the delimiter from the input stream get does not Detecting EOF 30 C A Beginner s Guide by Herbert Schildt You can detect when the end of the file is reached by using the member function eof which has this prototype bool eof It returns
399. n Rectangle p try p new Rectangle 10 8 Allocate a Rectangle object This catch bad_alloc xa calls the Rectangle constructor cout lt lt Allocation Failure n return 1 cout lt lt Area is lt lt p gt area cout lt lt n delete p Release the object This calls the Rectangle destructor return Q The output is shown here Constructing 10 by 8 rectangle Area is 80 Destructing 10 by 8 rectangle 32 C A Beginner s Guide by Herbert Schildt Notice that the arguments to the object s constructor are specified after the type name just as in other sorts of initializations Also because p contains a pointer to an object the arrow operator rather than the dot operator is used to call area You can allocate arrays of objects but there is one catch Since no array allocated by new can have an initializer you must make sure that if the class defines constructors one will be parameterless If you don t the C compiler will not find a matching constructor when you attempt to allocate the array and will not compile your program In this version of the preceding program a parameterless constructor is added so that an array of Rectangle objects can be allocated Also added is the function set which sets the dimensions of each rectangle Allocate an array of objects include lt iostream gt include lt new gt using namespace std class Rec
400. n hy int main Now set and show are D ob 3 inaccessible through D ob set 1 2 Error can t access set ob show Error can t access show return 0 To review when a base class is inherited as private public members of the base class become private members of the derived class This means that they are still accessible by members of the derived class but cannot be accessed by other parts of your program CRITICAL SKILL 10 3 Using protected Members As you know a private member of a base class is not accessible by a derived class This would seem to imply that if you wanted a derived class to have access to some member in the base class it would need to be public Of course making the member public also makes it available to all other code which may not be desirable Fortunately this implication is wrong because C allows you to create a protected member A protected member is public within a class hierarchy but private outside that hierarchy A protected member is created by using the protected access modifier When a member of a class is declared as protected that member is with one important exception private The exception occurs 9 C A Beginner s Guide by Herbert Schildt when a protected member is inherited In this case the protected member of the base class is accessible by the derived class Therefore by using protected you can create class members that are private to their clas
401. n 0 and 100 include lt iostream gt using namespace std int main int x for x 0 x lt 100 x if x 2 continue Continue the loop early when x is odd cout lt lt x lt lt return 0 Only even numbers are printed because an odd number will cause the continue statement to execute resulting in early iteration of the loop bypassing the cout statement Remember that the operator 29 C A Beginner s Guide by Herbert Schildt produces the remainder of an integer division Thus when x is odd the remainder is 1 which is true When x is even the remainder is 0 which is false In while and do while loops a continue statement will cause control to go directly to the conditional expression and then continue the looping process In the case of the for the increment part of the loop is performed then the conditional expression is executed and then the loop continues Progress Check 1 Within a loop what happens when a break is executed 2 What does continue do 3 Assuming a loop that encloses a switch does a break in the switch cause the loop to terminate Finish the C Help System This project puts the finishing touches on the C help system that was created by the previous projects This version adds the syntax for break continue and goto It also allows the user to request the syntax for more than one statement It does this by adding an outer loop that runs until the
402. n a is created but there are two calls to the destructor Let s see why this is the case When an object is passed to a function a copy of that object is made And this copy becomes the parameter in the function This means that a new object comes into existence When the function terminates the copy of the argument that is the parameter is destroyed This raises two fundamental questions First is the object s constructor called when the copy is made Second is the object s destructor called when the copy is destroyed The answers may at first surprise you When a copy of an argument is made during a function call the normal constructor is not called Instead the object s copy constructor is called A copy constructor defines how a copy of an object is made Later in this module you will see how to create a copy constructor However if a class does not explicitly define a copy constructor then C provides one by default The default copy constructor creates a bitwise that is identical copy of the object The reason a bitwise copy is made is easy to understand if you think about it Since a normal constructor is used to initialize some aspect of an object it must not be called to make a copy of an already existing object Such a call would alter the contents of the object When passing an object to a function you want to use the current state of the object not its initial state However when the function terminates
403. n access specifier for each base class inherited 25 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 10 7 When Constructor and Destructor Functions Are Executed Because a base class a derived class or both can contain constructors and or destructors it is important to understand the order in which they are executed Specifically when an object of a derived class comes into existence in what order are the constructors called When the object goes out of existence in what order are the destructors called To answer these questions let s begin with this simple program tinclude lt iostream gt using namespace std class E f public B cout lt lt Constructing base portion n B cout lt lt Destructing base portion n Ie class D public B public D cout lt lt Constructing derived portion n D cout lt lt Destructing derived portion n IF int main D ob do nothing but construct and destruct ob return 0 As the comment in main indicates this program simply constructs and then destroys an object called ob which is of class D When executed this program displays Constructing base portion Constructing derived portion Destructing derived portion Destructing base portion As the output shows first the constructor for B is executed followed by the constructor of D Next since ob is immediately destroyed in this program the destructor of D is ca
404. n scientific notation The width function sets the field width True an I O manipulator is used within an I O expression Here is one way to open a file for text input ifstream in test 1f in cout lt lt Cannot open file n return 1 Here is one way to open a file for text output ofstream out test if tout f cout lt lt Cannot open file n return 1 ios binary specifies that a file be opened for binary rather than text based I O True at end of file the stream variable will evaluate as false while strm get ch There are many solutions The following shows just one way Copy a file C A Beginner s Guide by Herbert Schildt tinclude lt iostream gt include lt fstream gt using namespace std int main int argc char argv char ch if arge 3 cout lt lt Usage copy lt source gt lt target gt n return 1 ifstream srce argv 1 ios in ios binary ifjitsrc cout lt lt Cannot open source file n return 1 ofstream targ argv 2 ios out ios binary 1f targ cout lt lt Cannot open target file n return 1 do srce get ch if src eof targ put ch while src eof src close targ close return 0 13 There are many solutions The following shows one simple way Merge two files 33 C A Beginner s Guide by Herbert Schildt include lt iostream gt include lt fstream gt using
405. n the variable to be set to 1 For example L101 0011 L010 1010 1111 1011 You can make use of the OR to change the uppercasing program used earlier into a lowercasing program as shown here Lowercase letters using bitwise OR include lt iostream gt using namespace std int main char ch for int i 0 i lt 10 i ch A i cout lt lt ch Use the bitwise OR to turn on bit 6 This statement turns on the 6th bit ch ch 32 ch is now lowercase cout lt lt ch lt lt T e f cout lt lt n return 0 19 C A Beginner s Guide by Herbert Schildt The output is shown here Aa Bb Cc Dd Ee Ff Gg Hh li Jj When the sixth bit is set each uppercase letter is transformed into its lowercase equivalent An exclusive OR usually abbreviated XOR will set a bit on only if the bits being compared are different as illustrated here 01111111 1011100 01 110 001l The XOR operator has an interesting property that makes it a simple way to encode a message When some value X is XORed with another value Y and then when that result is XORed with Y again X is produced That is given the sequence RI X Y R2 RI1 Y then R2 is the same value as X Thus the outcome of a sequence of two XORs using the same value produces the original value You can use this principle to create a simple cipher program in which some integer is the key that is used to both encode and decode a
406. n to Vehicle that computes the range you are enhancing its object oriented structure To add a function to Vehicle specify its prototype within Vehicle s declaration For example the following version of Vehicle specifies a member function called range which returns the range of the vehicle 6 C A Beginner s Guide by Herbert Schildt Declare the Vehicle class class Vehicle public int passengers number of passengers int fuelcap fuel capacity in gallons int mpg i fuel consumption in miles per gallon int range compute and return the range Declare the rangef i3 member function Because a member function such as range is prototyped within the class definition it need not be prototyped elsewhere To implement a member function you must tell the compiler to which class the function belongs by qualifying the function s name with its class name For example here is one way to code the range function Implement the range member function int Vehicle range return mpg fuelcap Notice the that separates the class name Vehicle from the function name range The is called the scope resolution operator It links a class name with a member name in order to tell the compiler what class the member belongs to In this case it links range to the Vehicle class In other words states that this range is in Vehicle s scope Several different classes can use the s
407. n writes num bytes to the associated stream from the buffer pointed to by buf As mentioned earlier streamsize is some form of integer defined by the C library It is capable of holding the largest number of bytes that can be transferred in any one I O operation The following program writes and then reads an array of integers 27 C A Beginner s Guide by Herbert Schildt Use read and write include lt iostream gt include lt fstream gt using namespace std int main int n 5 1 2 3 4 5 register int 1 ofstream out test ilos out ios binary 1f out cout lt lt Cannot open file n return 1 out write char amp n sizeof n Write a block of data out close for i 0 i lt 5 i clear array n i 0 ifstream in test los in ios binary if in cout lt lt Cannot open file n return 1 in read char amp n sizeof mn _ Read a block of data for i 0 i lt 5 i show values read from file cout lt lt n i lt lt in close return O Note that the type casts inside the calls to read and write are necessary when operating on a buffer that is not defined as a character array If the end of the file is reached before num characters have been read then read simply stops and the buffer will contain as many characters as were available You can find out how many characters have been read using another
408. nal market Progress Check 1 What are the seven basic types 2 What is the difference between signed and unsigned integers 3 Canachar variable be used like a little integer Answer Key 1 The seven basic types are char wchar_t int float double bool and void 2 Asigned integer can hold both positive and negative values An unsigned integer can hold only positive values 3 Yes Ask the Expert Q Why does C specify only minimum ranges for its built in types rather than stating these precisely A By not specifying precise ranges C allows each compiler to optimize the data types for the execution environment This is part of the reason that C can create high performance software The ANSI ISO C standard simply states that the built in types must meet certain requirements For example it states that an int will have the natural size suggested by the architecture of the execution environment Thus in a 32 bit environment an int will be 32 bits long In a 16 bit environment an int will be 16 bits long It would be an inefficient and unnecessary burden to force a 16 bit compiler to implement int with a 32 bit range for example C s approach avoids this Of course the C standard does specify a minimum range for the built in types that will be available in all environments Thus if you write your programs in such a way that these minimal ranges are not exceeded then your program will be portable to othe
409. namespace std int main int argc char argv char ch iffarge 4 cout lt lt Usage return 1 ifstream srel argv 1 los ifi tsrel cout lt lt return 1 lfstream src2 argv 2 los 1f sre2 cout lt lt return 1 ofstream targ argv 3 if targ cout lt lt return 1 Copy first source file do srcl get ch 1f srel eof targ put ch while srcl eof Copy second source file do srce2 get ch 1f sre2 eof targ put ch while sre2 eo0f srcl close sre2 close targ close return 0 14 MyStrm seekg 300 ios beg 34 merge lt sourcel gt lt source2 gt lt target gt n in ios binary Cannot open ist source file n in ios binary Cannot open 2nd source file n 1os out 10s binary Cannot open target file n C A Beginner s Guide by Herbert Schildt Module 12 Exceptions Templates and Other Advanced Topics 1 C exception handling is built upon three keywords try catch and throw In the most general terms program statements that you want to monitor for exceptions are contained in a try block If an exception that is an error occurs within the try block it is thrown using throw The exception is caught using catch and processed When catching exceptions of both base and derived classes the derived classes must precede the base class in a catch list void fun
410. ndex changes faster than the left You should remember that storage for all array elements is determined at compile time Also the memory used to hold an array is required the entire time that the array is in existence In the case of a two dimensional array you can use this formula to determine the number of bytes of memory that are needed bytes number of rows x number of columns x number of bytes in type Therefore assuming four byte integers an integer array with dimensions 10 5 would have 10x5x4 or 200 bytes allocated 7 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 4 3 Multidimensional Arrays C allows arrays with more than two dimensions Here is the general form of a multidimensional array declaration type name size1 size2 sizeN For example the following declaration creates a 4x10x3 integer array int multidim 4 10 3 Arrays of more than three dimensions are not often used due to the amount of memory required to hold them Remember storage for all array elements is allocated during the entire lifetime of an array When multidimensional arrays are used large amounts of memory can be consumed For example a four dimensional character array with dimensions 10 6 9 4 would require 10x6x9x4 or 2 160 bytes If each array dimension is increased by a factor of 10 each that is 100x60x90x40 then the memory required for the array increases to 21 600 000 bytes As you can see large multidimensi
411. ndition n break case 6 cout lt lt The break n n cout lt lt break n break case 7 cout lt lt The continue n n cout lt lt continue n break case S cout lt lt The goto n n cout lt lt goto label n break cout lt lt n return 0 6 Here is a sample run Help on Le 1f 2 switch da TOL 4 while 5 do while 6 break Te Continue 8 goto Choose one q to quit 1 The if 1f condition statement else statement Help on Ee LI switch ENA while do while break continue goto CUNO RB WD Choose one q to quit 6 33 C A Beginner s Guide by Herbert Schildt The break break Help on te Ir 2 SWirtON 3s TOT 4 while 5a do while 6 break 7 continue Ox GOTO Choose one q to quit q CRITICAL SKILL 3 8 Nested Loops As you have seen in some of the preceding examples one loop can be nested inside of another Nested loops are used to solve a wide variety of problems and are an essential part of programming So before leaving the topic of C s loop statements let s look at one more nested loop example The following program uses a nested for loop to find the factors of the numbers from 2 to 100 Use nested loops to find factors between 2 and 100 ae include lt iostream gt using namespace std int main for int 1 2 1 lt 100 i f cout lt lt Factors of lt lt i lt lt f
412. nents C defines two main flavors of floating point types float and double which represent single and double precision values respectively Of the two double is probably the most commonly used To declare a variable of type double use a statement similar to that shown here double result Here result is the name of the variable which is of type double Because result has a floating point type it can hold values such as 88 56 0 034 or 107 03 To better understand the difference between int and double try the following program 22 C A Beginner s Guide by Herbert Schildt f This program illustrates the differences between int and double include lt Lostream gt using namespace std int mainii int ivar ii this declares an int variable double dvar this declares a floating point variable ivar 100 assign ivar the value 100 dvar 100 0 assign dvar the value 100 0 cout lt lt Original value of ivar lt lt ivar lt lt n cout lt lt Original value of dvar lt lt dwar lt lt n cout lt lt An print a blank line 4 Output a blank line i now divide both by 3 ivar ivar 3 dvar dvar 3 0 cout lt lt ivar after division lt lt ivar lt lt n cout lt dvar after division lt lt dvar lt lt n return 0 The output from this program is shown here Original value of ivar 100 Original value of dvar 100 ivar after
413. ng using statements and assignments are valid using CounterNameSpace lowerbound only lowerbound is visible lowerbound 10 OK because lowerbound is visible using namespace CounterNameSpace all members are visible upperbound 100 OK because all members are now visible The following program illustrates using by reworking the counter example from the Demonstrate using include lt iostream gt using namespace std namespace CounterNamespace int upperbound int lowerbound class counter int count public counter int n 1f n lt upperbound count n else count upperbound void reset int n 1f n lt upperbound count n int run if count gt lowerbound return count else return lLlowerbound 39 C A Beginner s Guide by Herbert Schildt int main f use only upperbound from CounterNamespace using CounterNameSpace upperbound _ Use a specific member of CounterNameSpace now no qualification needed to set upperbound upperbound 100 qualification still needed for lowerbound etc CounterNamespace lowerbound 0 CounterNamespace counter ob1l 10 int i do i obl run cout lt lt 1 lt lt while i gt CounterNameSpace lowerbound cout lt lt endl Now use entire CounterNameSpace using namespace CounterNameSpace q Use the entire CounterNameSpace counter ob2 20 do 1 ob2 run co
414. ng curly brace on the line that follows main marks the start of the main function code The int that precedes main specifies the type of data returned by main As you will learn C supports several built in data types and int is one of them It stands for integer The next line in the program is cout lt lt C 1S power programming 13 C A Beginner s Guide by Herbert Schildt This is a console output statement It causes the message C is power programming to be displayed on the screen It accomplishes this by using the output operator lt lt The lt lt operator causes whatever expression is on its right side to be output to the device specified on its left side cout is a predefined identifier that stands for console output and generally refers to the computer s screen Thus this statement causes the message to be output to the screen Notice that this statement ends with a semicolon In fact all C statements end with a semicolon The message C is power programming is a string In C a string is a sequence of characters enclosed between double quotes Strings are used frequently in C The next line in the program is return U This line terminates main and causes it to return the value O to the calling process which is typically the operating system For most operating systems a return value of 0 signifies that the program is terminating normally Other values indicate that the program i
415. ngle Instead an abstract class must be used only as a base that other classes will inherit The reason that an abstract class cannot be used to declare an object is because one or more of its functions have no definition Because of this the shapes array in the preceding program has been shortened to 4 and a generic TwoDShape object is no longer created As the program illustrates even if the base class is abstract you still can use it to declare a pointer of its type which can be used to point to derived class objects Module 10 Mastery Check 10 11 A class that is inherited is called a class The class that does the inheriting is called a class Does a base class have access to the members of a derived class Does a derived class have access to the members of a base class Create a derived class of TwoDShape called Circle Include an area function that computes the area of the circle How do you prevent a derived class from having access to a member of a base class Show the general form of a constructor that calls a base class constructor Given the following hierarchy class Alpha class Beta public Alpha Class Gamma public Beta in what order are the constructors for these classes called when a Gamma object is instantiated How can protected members be accessed A base class pointer can refer to a derived class object Explain why this is important as it relates to function overriding What is a pure v
416. nnot alter the arguments used to call the function In this book all of the programs up to this point have used the call by value method For example consider the reciprocal function in this program Changing a call by value parameter does not affect the argument tinclude lt iostream gt using namespace std double reciprocal double x int main double t 10 0 cout lt lt Reciprocal of 10 0 is lt lt reciprocal t lt lt n cout lt lt Value of t is still lt lt t lt lt n F return Return the reciprocal of a value double reciprocal double x x 1 x create reciprocal This does not change the value of t inside main return x takes place inside reciprocal the only thing modified is the local variable x The variable t used as an argument will still have the value 10 and is unaffected by the operations inside the function 2 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 6 3 Using a Pointer to Create a Call by Reference Even though C s default parameter passing convention is call by value it is possible to manually create a call by reference by passing the address of an argument that is a pointer to a function It is then possible to change the value of the argument outside of the function You saw an example of this in the preceding module when the passing of pointers was discussed As you know pointers are passed to f
417. nstrates the if else if ladder 5 C A Beginner s Guide by Herbert Schildt Demonstrate an if else if ladder include lt iostream gt using namespace std int main int x for x 0 x lt 6 x if x 1 cout lt lt x is one n else if x 2 cout lt lt x is two n else if x 3 cout lt lt x is three n An if else if ladder else if x 4 cout lt lt x is four n else cout lt lt x is not between 1 and 4 n return OQ The program produces the following output is not between 1 and 4 is one is two is three is four is not between 1 and 4 ee As you can see the default else is executed only if none of the preceding if statements succeeds Progress Check 1 The condition controlling the if must use a relational operator True or false 2 To what if does an else always associate 3 What is an if else if ladder Answer Key 1 The condition controlling the if must use a relational operator True or false 2 To what if does an else always associate 3 What is an if else if ladder 6 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 3 2 The switch Statement The second of C s selection statements is the switch The switch provides for a multiway branch Thus it enables a program to select among several alternatives Although a series of nested if statements can perform multiway tests for many situations the switch is a more efficient approach
418. nstructor for Vehicle Vehicle int p int int m int range compute and return the range Implement the Vehicle constructor Vehicle Vehicle int p int f int m Vehicle s constructor passengers p initializes passengers fuelcap f fuelcap and mpg Mpg Mm Implement the range member function int Vehicle range return mpg fuelecap int main Pass values to Vehicle constructor Vehicle minivan 7 16 21 Pass the vehicle Vehicle sportscar 2 14 12 information to Vehicle using Its constructor int rangel range2 Compute the ranges assuming a full tank of gas rangel minivan range ranges sportscar range cout lt lt Minivan can carry lt lt minivan passengers lt lt with a range of lt lt rangel lt lt n cout lt lt Sportscar can carry lt lt sportscar passengers lt lt with a range of lt lt range2 lt lt n return 0 Both minivan and sportscar were initialized by the Vehicle constructor when they were created Each object is initialized as specified in the parameters to its constructor For example in the line Vehicle minivan 7 16 21 20 C A Beginner s Guide by Herbert Schildt the values 7 16 and 21 are passed to the Vehicle constructor Therefore minivan s copy of passengers fuelcap and mpg will contain the values 7 16 and 21 respectively Thus the output from this program is the
419. nt bool b void print int i void print long i void print char ch void print char str void print double d int main printlin true 10 printin 10 5 printlin This is a test println x println 99L 10 16 C A Beginner s Guide by Herbert Schildt printin 123 23 10 print Here are some values print false print 88 3 print 100000L 3 print 100 01 println Done return 0 Here are the println functions void println bool b int ident if ident for int i 0 1 lt ident i cout lt lt 1f b cout lt lt true n else cout lt lt false n void println int i int ident 1 ident for int 1 0 1 lt ident i cout lt lt cout lt lt i lt lt n void println long i int ident if ident for int 1 0 1 lt ident i cout lt lt cout lt lt 1 lt lt n void println char ch int ident 1f ident for int i 0 1 lt ident i cout lt lt cout lt lt ch lt lt n 17 C A Beginner s Guide by Herbert Schildt void println char str int ident 1f ident for int 1 0 i lt ident i cout lt lt cout lt lt str lt lt n void println double d int ident 1f ident for int i 0 i lt ident i cout lt lt cout lt lt d lt lt n Here are the print functions void print bool b int ident 1
420. nt i 0 i lt ob2 len i newset newset ob2 members i return newset return updated set 48g C A Beginner s Guide by Herbert Schildt As you can see these functions utilize the previously defined versions of the and operators to help perform their operations In the case of set union a new set is created that contains the elements of the first set Then the elements of the second set are added Because the operation only adds an element if it is not already part of the set the resulting set is the union without duplication of the two sets The set difference operator subtracts matching elements 9 Here is the complete code for the Set class along with a main function that demonstrates it Project 9 1 A set class for characters 49 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std const int MaxSize 100 class Set int len number of members char members MaxSize this array holds the set The find function is private because it is not used outside the Set class int find char ch Eind an element public Construct a null set Set len OQ Return the number of elements in the set int getLength return len wold showset display the set bool isMember char ch check for membership eet operator char ch add an element eet operator char ch remove an element Set operator Set ob2
421. ntioned earlier the type of the exception must match the type specified in a catch statement For example in the preceding program if you change the type in the catch statement to double then the exception will not be caught and abnormal termination will occur This change is shown here This example will not work include lt iostream gt using namespace std int main cout lt lt start n try start a try block cout lt lt Inside try block n throw 99 throw an error cout lt lt This will not execute catch double i won t work for an int exception cout lt lt Caught an exception value is cout lt lt i lt lt n This can t catch an int exception cout lt lt end return OQ This program produces the following output because the integer exception will not be caught by the catch double i statement Of course the final message indicating abnormal termination will vary from compiler to compiler start Inside try block Abnormal program termination An exception thrown by a function called from within a try block can be handled by that try block For example this is a valid program 4 C A Beginner s Guide by Herbert Schildt Throwing an exception from a function called from within a try block include lt iostream gt using namespace std void Xtest int test cout lt lt Inside Xtest test is lt lt test lt lt n if
422. nts Second they can result in more efficient executable code because the operand is evaluated only once For these reasons you will often see the compound assignment operators used in professionally written C programs CRITICAL SKILL 2 8 Type Conversion in Assignments When variables of one type are mixed with variables of another type a type conversion will occur In an assignment statement the type conversion rule is easy The value of the right side expression side of the assignment is converted to the type of the left side target variable as illustrated here Lat x char ch float f ch xi linea I x fe line 2 7 f phi 7 done 3 77 f x line 4 In line 1 the high order bits of the integer variable x are lopped off leaving ch with the lower 8 bits If x were between 128 and 127 ch and x would have identical values Otherwise the value of ch would reflect only the lower order bits of x In line 2 x will receive the nonfractional part of f In line 3 f will convert the 8 bit integer value stored in ch to the same value in the floating point format This also happens in line 4 except that f will convert an integer value into floating point format When converting from integers to characters and long integers to integers the appropriate number of high order bits will be removed In many 32 bit environments this means that 24 bits will be lost when going from an integer to a character and 16 bits wi
423. nts such as 14 C A Beginner s Guide by Herbert Schildt minivan passengers 7 minivan fuelcap 16 minivan mpg 21 An approach like this would never be used in professionally written C code Aside from being error prone you might forget to set one of the fields there is simply a better way to accomplish this task the constructor A constructor initializes an object when it is created It has the same name as its class and is syntactically similar to a function However constructors have no explicit return type The general form of a constructor is shown here class name constructor code Typically you will use a constructor to give initial values to the instance variables defined by the class or to perform any other startup procedures required to create a fully formed object The complement of the constructor is the destructor In many circumstances an object will need to perform some action or series of actions when it is destroyed Local objects are created when their block is entered and destroyed when the block is left Global objects are destroyed when the program terminates There are many reasons why a destructor may be needed For example an object may need to deallocate memory that it had previously allocated or an open file may need to be closed In C it is the destructor that handles these types of operations The destructor has the same name as the constructor but is preceded by a Like cons
424. nue to associate the and the amp with the variable name that each modifies rather than with the type name Progress Check 1 How is a reference parameter declared g C A Beginner s Guide by Herbert Schildt 2 When calling a function that uses a reference parameter must you precede the argument with an amp 3 Inside a function that receives a reference parameter do operations on that parameter need to be preceded with an or amp CRITICAL SKILL 6 5 Returning References A function can return a reference In C programming there are several uses for reference return values Some of these uses must wait until later in this book However there are some that you can use now When a function returns a reference it returns an implicit pointer to its return value This gives rise to a rather startling possibility the function can be used on the left side of an assignment statement For example consider this simple program Returning a reference include lt iostream gt using namespace std double amp f return a reference Here fi retums a reference to a double double val 100 0 int main double x cout lt lt lt lt n display val s value x assign value of val to x cout lt lt x lt lt n display x s value 99 1 change val s value cout lt lt lt lt n display val s new value return 0 This function
425. o Notice that b the divisor is tested for zero using if b This approach works because when b is zero the condition controlling the if is false and the else executes Otherwise the condition is true non zero and the division takes place It is not necessary and would be considered bad style by many C programmers to write this if as shown here if 5 0 gout lt lt a Artifact lt lt Tinj This form of the statement is redundant and potentially inefficient Nested ifs A nested if is an if statement that is the target of another if or else Nested ifs are very common in programming The main thing to remember about nested ifs in C is that an else statement always refers to the nearest if statement that is within the same block as the else and not already associated with an else Here is an example 1 1 1 j result 1 ifik result 2 else result 3 this else is associated with if k else result 4 this else is associated with if 1 As the comments indicate the final else is not associated with if j even though it is the closest if without an else because it is not in the same block Rather the final else is associated with if i The inner else is associated with if k because that is the nearest if You can use a nested if to add a further improvement to the Magic Number program This addition provides the player with feedback about a wrong guess Magic Number program 2nd improve
426. o for t2 n t2 showStyle t2 showDim cout lt lt Area is lt lt t2 area lt lt n return 0 The output from this program is shown here Info for tl Triangle is isosceles Width and height are 4 and 4 Area is 8 Info for t2 Triangle is right Width and height are 8 and 12 Area is 48 Here TwoDShape defines the attributes of a generic two dimensional shape such as a square rectangle triangle and so on The Triangle class creates a specific type of TwoDShape inthis case a triangle The Triangle class includes all of TwoDShape and adds the field style the function area and the function showStyle A description of the type of triangle is stored in style area computes and returns the area of the triangle and showStyle displays the triangle style The following line shows how Triangle inherits TwoDShape class Triangle public TwoDShape Here TwoDShape is a base class that is inherited by Triangle which is a derived class As this example shows the syntax for inheriting a class is remarkably simple and easy to use 3 C A Beginner s Guide by Herbert Schildt Because Triangle includes all of the members of its base class TwoDShape it can access width and height inside area Also inside main objects t1 and t2 can refer to width and height directly as if they were part of Triangle Figure 10 1 depicts conceptually how TwoDShape is incorporated into Triangle One ot
427. o or from pointers The expression p1 p1 9 makes p1 point to the ninth element of p1 s base type beyond the one to which it is currently pointing Although you cannot add pointers you can subtract one pointer from another provided they are both of the same base type The remainder will be the number of elements of the base type that separate the two pointers Other than addition and subtraction of a pointer and an integer or the subtraction of two pointers no other arithmetic operations can be performed on pointers For example you cannot add or subtract float or double values to or from pointers To graphically see the effects of pointer arithmetic execute the next short program It creates an int pointer i and a double pointer f It then adds the values O through 9 to these pointers and displays the results Observe how each address changes relative to its base type each time the loop is repeated For most 32 bit compilers i will increase by 4s and f will increase by 8s Notice that when using a pointer in a cout statement its address is automatically displayed in the addressing format applicable to the CPU and environment include lt iostream gt using namespace std int main int i 3 10 double f g 10 int x i j g Display the addresses produced by adding x to each pointer for x 0 x lt 10 X cout lt lt 14x lt lt fo gg X lt lt A n 23 C A Beginner s Guide by
428. o show you how an overloaded relational operator can be implemented the following function overloads relative to the ThreeD class Overload bool ThreeD operator ThreeD op2 LE x op2 x amp amp y op2 y amp amp Zz op2 z return true alse return false Once operator has been implemented the following fragment is perfectly valid ThreeD a 1 1 1 b 2 2 2 if a b cout lt lt a equals b n else cout lt lt a does not equal b n There are some restrictions to overloading operators First you cannot alter the precedence of any operator Second you cannot alter the number of operands required by the operator although your operator function could choose to ignore an operand Finally except for the function call operator operator functions cannot have default arguments Nearly all of the C operators can be overloaded This includes specialized operators such as the array indexing operator the function call operator and the gt operator The only operators that you cannot overload are shown here The is a special purpose operator whose use is beyond the scope of this book Creating a Set Class Operator overloading helps you create classes that can be fully integrated into the C programming environment Consider this point by defining the necessary operators you enable a class type to be used in a program in just the same way as you would use
429. object is passed as a parameter returned by a function or used in an initialization the copy constructor is called to duplicate the object Remember the copy constructor is not called when one object is assigned to another For example the following sequence will not invoke the copy constructor MyClass x MyClass y x y copy constructor not used here Again assignments are handled by the assignment operator not the copy constructor The following program demonstrates a copy constructor 14 C A Beginner s Guide by Herbert Schildt Copy constructor invoked when passing an object to a function include lt iostream gt using namespace std class MyClass int val int copynumber public Normal constructor MyClass int i val i copynumber 0 cout lt lt Inside normal constructor n Copy constructor MyClass const MyClass amp 0 This is the MyClass copy constructor val o val copynumber o copynumber 1 cout lt lt Inside copy constructor n MyClass Lf copynumber 0 cout lt lt Destructing original n else cout lt lt Destructing copy lt lt copynumber lt lt n int getval return val void display MyClass ob cout lt lt ob getval lt lt n int main MyClass a 10 display a e The copy constructor is called return This program displays the following output
430. ode to display a menu input the user s choice check for a valid response and display information about the item selected The program also loops until q is pressed If you think about it it is clear that the menu the check for a valid response and the display of the information are integral to the help system How user input is obtained and whether repeated requests should be processed are not Thus you will create a class that displays the help information the help menu and checks for a valid selection These functions will be called helpon showmenu and isvalid respectively 3 Declare the Help class as shown here f A class that encapsulates a help system class Help public void helpon char what void showmenu bool isvalid char ch Notice that this is a function only class no instance variables are needed As explained data only and code only classes are perfectly valid Question 9 in the Mastery Check adds an instance variable to the Help class 4 Create the helpon function as shown here Display help information void Help helpon char what switch what case l cout lt lt The if n n 10 C A Beginner s Guide by Herbert Schildt cout lt lt if condition statement n cout lt lt else statement n break case 2 cout lt lt The switch n n cout lt lt switch expression n cout lt lt case constant n cout lt lt statement seq
431. of num is set using its class name in this line Test num 100 It is also accessible through an object as in this line a num 200 Either approach is valid static Member Functions It is also possible for a member function to be declared as static but this usage is not common A member function declared as static can access only other static members of its class Of course a static member function may access non static global data and functions A static member function does not have a this pointer Virtual static member functions are not allowed Also it cannot be declared as const or volatile A static member function can be invoked by an object of its class or it can be called independent of any object using the class name and the scope resolution operator For example consider this program It defines a static variable called count that keeps count of the number of objects currently in existence Demonstrate a static member function include lt iostream gt using namespace std class Test static int count public Test count cout lt lt Constructing object lt lt count lt lt endl AA C A Beginner s Guide by Herbert Schildt Test f cout lt lt Destroying object lt lt count lt lt endl count A static member function static int numObjects return count int Test count int main Test a b c cout lt lt There are now lt lt T
432. ogramming environment When you overload an operator you define the meaning of an operator for a particular class For example a class that defines a linked list might use the operator to add an object to the list A class that implements a stack might use the to push an object onto the stack Another class might use the operator in an entirely different way When an operator is overloaded none of its original meaning is lost It is simply that a new operation relative to a specific class is defined Therefore overloading the to handle a linked list for example does not cause its meaning relative to integers that is addition to be changed Operator overloading is closely related to function overloading To overload an operator you must define what the operation means relative to the class to which it is applied To do this you create an operator function The general form of an operator function is type classname operator arg list operations Here the operator that you are overloading is substituted for the and type is the type of value returned by the specified operation Although it can be of any type you choose the return value is often of the same type as the class for which the operator is being overloaded This correlation facilitates the use of the overloaded operator in compound expressions Thespecificnatureof arg list is determined by several factors described in the sections that follow Operato
433. oint Turns on showpoint flag Output Table 11 1 The C I O Manipulators 16 C A Beginner s Guide by Herbert Schildt Manipulator Purpose Input Output showpos Turns on showpos flag Output skipws Turns on skipws flag Input unitbuf Turns on unitbuf flag Output uppercase Turns on uppercase flag Output WS Skips leading whitespace Input Table 11 1 The C I O Manipulators continued manipulator is used as part of a larger I O expression Here is a sample program that uses manipulators to control the format of its output Demonstrate an I O manipulator include lt iostream gt include lt iomanip gt using namespace std int main cout lt lt setprecision 2 lt lt 1000 243 lt lt endl cout lt lt setw 20 lt lt Hello i ii return 0 Use O manipulators It produces this output 164 003 Hello there Notice how the manipulators occur in the chain of I O operations Also notice that when a manipulator does not take an argument such as endl in the example it is not followed by parentheses The following program uses setiosflags to set the scientific and showpos flags Use setiosflags include lt iostream gt include lt iomanip gt using namespace std 17 C A Beginner s Guide by Herbert Schildt int main cout lt lt setiosflags ios showpos lt lt 4 Use seetiosflags setiosflags ios scientific lt lt
434. oints to object of type D which 18 an object derived from B F F 27 C A Beginner s Guide by Herbert Schildt A base pointer can be used to access only those parts of a derived object that were inherited from the base class Thus in this example p can be used to access all elements of D_ob inherited from B_ob However elements specific to D_ob cannot be accessed through p Another point to understand is that although a base pointer can be used to point to a derived object the reverse is not true That is you cannot access an object of the base type by using a derived class pointer As you know a pointer is incremented and decremented relative to its base type Therefore when a base class pointer is pointing at a derived object incrementing or decrementing it will not make it point to the next object of the derived class Instead it will point to what it thinks is the next object of the base class Therefore you should consider it invalid to increment or decrement a base class pointer when it is pointing to a derived object The fact that a pointer to a base type can be used to point to any object derived from that base is extremely important and fundamental to C As you will soon learn this flexibility is crucial to the way C implements runtime polymorphism References to Derived Types Similar to the action of pointers just described a base class reference can be used to refer to an object of a derived type The mos
435. ome with Windows programming Indeed it is the most commonly used language for Windows development However none of the programs in this book use the Windows Graphic User Interface GUI The reason for this is easy to understand Windows programs are by their nature large and complex The overhead required to create even a minimal Windows skeletal program is 50 to 70 lines of code To write Windows programs that demonstrate the features of C would require hundreds of lines of code each In contrast console based programs are much shorter and are the type of programs normally used to teach programming Once you have mastered C you will be able to apply your knowledge to Windows programming with no trouble The First Sample Program Line by Line Although Sample cpp is quite short it includes several key features that are common to all C programs Let s closely examine each part of the program The program begins with the lines Je This is a simple C program Call this file Sample cpp a This is a comment Like most other programming languages C lets you enter a remark into a program s source code The contents of a comment are ignored by the compiler The purpose of a comment is to describe or explain the operation of a program to anyone reading its source code In the case of this comment it identifies the program In more complex programs you will use comments to help explain what each feature of the program is for and how it
436. ompiler needs to know this information prior to the first time the function is called This is why the prototype occurs before main The only function that does not require a prototype is main since it is predefined by C The keyword void which precedes both the prototype for myfunc and its definition formally states that myfunc does not return a value In C functions that don t return values are declared as void CRITICAL SKILL 5 3 Using Arguments It is possible to pass one or more values to a function that you create A value passed to a function is called an argument Thus arguments are a way to get information into a function When you create a function that takes one or more arguments variables that will receive those arguments must also be declared These variables are called the parameters of the function Here is an example that defines a function called box that computes the volume of a box and displays the result It has three parameters void box int length int width int height cout lt lt volume of box is lt lt length width height lt lt n I 3 C A Beginner s Guide by Herbert Schildt In general each time box is called it will compute the volume by multiplying the values passed to its parameters length width and height Notice how the parameters are declared Each parameter s declaration is separated from the next by a comma and the parameters are contained within the
437. on signals the end of a statement That is each individual statement must end with a semicolon As you know a block is a set of logically connected statements that is surrounded by opening and closing braces A block is not terminated with a semicolon Since a block is a group of statements with a semicolon after each statement it makes sense that a block is not terminated by a semicolon instead the end of the block is indicated by the closing brace C does not recognize the end of the line as the end of a statement only a semicolon terminates a statement For this reason it does not matter where on a line you put a statement For example to C x y y y 13 COUT lt lt x lt lt 1 lt lt yJ is the same as Furthermore the individual elements of a statement can also be put on separate lines For example the following is perfectly acceptable cout lt lt This is a long line The sum is lt lt a b ct d e f Breaking long lines in this fashion is often used to make programs more readable It can also help prevent excessively long lines from wrapping Indentation Practices You may have noticed in the previous examples that certain statements were indented C is a free form language meaning that it does not matter where you place statements relative to each other on a line However over the years a common and accepted indentation style has developed that allows for very readable programs This book
438. onal arrays may cause a shortage of memory for other parts of your program Thus a program with arrays of more than two or three dimensions may find itself quickly out of memory Progress Check 1 Each dimension in a multidimensional array is specified with its own set of brackets True or false 2 Show how to declare a two dimensional integer array called list with the dimensions 4 9 3 Given list from the preceding question show how to access element 2 3 OLSE Sorting an Array Because a one dimensional array organizes data into an indexable linear list it isthe perfect data structure for sorting In this project you will learn a simple way to sort an array As you may know there are a number of different sorting algorithms The quick sort the shaker sort and the shell sort are just three However the best known simplest and easiest to understand sorting algorithm is called the bubble sort While the bubble sort is not very efficient in fact its performance is unacceptable for sorting large arrays it may be used effectively for sorting small ones Step by Step 1 Create a file called Bubble cpp g C A Beginner s Guide by Herbert Schildt 2 The bubble sort gets its name from the way it performs the sorting operation It uses repeated comparison and if necessary exchange of adjacent elements in the array In this process small values move toward one end and large ones toward the other end The process is c
439. onal data types and its most commonly used operators We will also take a closer look at variables and examine the expression C A Beginner s Guide by Herbert Schildt Why Data Types Are Important The data type of a variable is important because it determines the operations that are allowed and the range of values that can be stored C defines several types of data and each type has unique characteristics Because data types differ all variables must be declared prior to their use and a variable declaration always includes a type specifier The compiler requires this information in order to generate correct code In C there is no concept of a type less variable A second reason that data types are important to C programming is that several of the basic types are closely tied to the building blocks upon which the computer operates bytes and words Thus C lets you operate on the same types of data as does the CPU itself This is one of the ways that C enables you to write very efficient system level code CRITICAL SKILL 2 1 The C Data Types C provides built in data types that correspond to integers characters floating point values and Boolean values These are the ways that data is commonly stored and manipulated by a program As you will see later in this book C allows you to construct more sophisticated types such as classes structures and enumerations but these too are ultimately composed of the built in ty
440. onceptually similar to bubbles finding their own level in a tank of water The bubble sort operates by making several passes through the array exchanging out of place elements when necessary The number of passes required to ensure that the array is sorted is equal to one less than the number of elements in the array Here is the code that forms the core of the bubble sort The array being sorted is called nums This is the bubble sort for a l1 a lt size a for b size 1 be a b i f nums b 1 gt nums b if out of order exchange elements t nums b 1 nums b 1 nums b nums b t Notice that the sort relies on two for loops The inner loop checks adjacent elements in the array looking for out of order elements When an out of order element pair is found the two elements are exchanged With each pass the smallest element of those remaining moves into its proper location The outer loop causes this process to repeat until the entire array has been sorted 3 Here isthe entire Bubble cpp program 9 C A Beginner s Guide by Herbert Schildt i Project 4 1 Demonstrate the Bubble sort f tinclude lt iostream gt include lt cstdlib gt using namespace std int main int nums 10 int a b t int size size 10 number of elements to sort give the array some random initial values for t 0 t lt size t nums t rand display original array cout lt lt O
441. one object a is created and destroyed No temporary objects are needed by the program A Potential Problem When Passing Objects Even when objects are passed to functions by means of the normal call by value parameter passing mechanism which in theory protects and insulates the calling argument it is still possible for a side effect to occur that may affect or even damage the object used as an argument For example if an object allocates some system resource such as memory when it is created and frees that resource when it is destroyed then its local copy inside the function will free that same resource when its destructor is called This is a problem because the original object is still using this resource This situation usually results in the original object being damaged One solution to this problem is to pass an object by reference as shown in the preceding section In this case no copy of the object is made and thus no object is destroyed when the function returns As explained passing objects by reference can also speed up function calls because only the address of the object is being passed However passing an object by reference may not be applicable to all cases Fortunately a more general solution is available you can create your own version of the copy constructor Doing so lets you define precisely how a copy of an object is made allowing you to avoid the type of problems just described However before examining the
442. one or more parameters of a particular function You can accomplish this with a reference parameter When you use a reference parameter the address not the value of an argument is automatically passed to the function Within the function operations on the reference parameter are automatically dereferenced so there is no need to use the pointer operators 4 C A Beginner s Guide by Herbert Schildt A reference parameter is declared by preceding the parameter name in the function s declaration with an amp Operations performed on a reference parameter affect the argument used to call the function not the reference parameter itself To understand reference parameters let s begin with a simple example In the following the function f takes one reference parameter of type int Using a reference parameter include lt iostream gt using namespace std wold flint amp 1 here i is a reference parameter int main Declare a reference parameter int val 1 cout lt lt Old value for val lt lt val lt lt n fF val pass address of val to f cout lt lt New value for val lt lt val lt lt n return 0 Assign a value to the void flint amp i variable referred to by i f i 10 this modifies calling argument This program displays the following output Old value for val 1 New value for val 10 Pay special attention to the definition of f shown here void f
443. only the extra information it needs for its own specific application This is part of the value of inheritance it allows the reuse of code 24 C A Beginner s Guide by Herbert Schildt This example illustrates one other important point In a class hierarchy if a base class constructor requires parameters then all derived classes must pass those parameters up the line This is true whether or not a derived class needs parameters of its own CRITICAL SKILL 10 6 Inheriting Multiple Base Classes In C it is possible for a derived class to inherit two or more base classes at the same time For example in this short program D inherits both B1 and B2 An example of multiple base classes include lt iostream gt using namespace std class Bl protected int x public void showx cout lt lt x lt lt mn class EZ protected int y public void showy cout lt lt y lt lt n F Inherit multiple base classes class D public Bl public B2 Here D inherits both B1 public and B2 at the same time x and y are accessible because they are protected in Bl and B2 not private void set int i int Jj x i y j int main D ob ob set 10 20 provided by D ob showx Erom Bil ob showy Erom B2 return As this example illustrates to cause more than one base class to be inherited you must use a comma separated list Further be sure to use a
444. ons of the machine instructions As programs continued to grow high level languages were developed to give programmers more tools with which to handle the complexity The first widely used computer language was of course FORTRAN While FORTRAN was a very impressive first step it is hardly a language that encourages clear easy to understand programs The 1960s gave birth to structured programming which is the method of programming encouraged by languages such as C With structured languages it was for the first time possible to write moderately complex programs fairly easily However even with structured programming methods once a project reaches a certain size its complexity exceeds what a programmer can manage By the late 1970s many projects were near or at this point In response to this problem a new way to program began to emerge object oriented programming OOP Using OOP a programmer could handle larger more complex programs The trouble was that C did not support object oriented programming The desire for an object oriented version of C ultimately led to the creation of C In the final analysis although C is one of the most liked and widely used professional programming languages in the world there comes a time when its ability to handle complexity is exceeded Once a program reaches a certain size it becomes so complex that it is difficult to grasp as a totality The 3 C A Beginner s Guide by Herbert Schildt p
445. operator lt lt ostream amp stream ThreeD obj friend istream Soperator gt gt istream amp stream ThreeD amp obj t Display X Y 4 coordinates ThreeD inserter ostream amp 0perator lt lt ostream amp stream ThreeD obj m m stream lt lt obj x lt lt stream lt lt obj y lt lt stream lt lt obj z lt lt n return stream return the stream Get three dimensional values ThreeD extractor istream amp operator gt gt istream amp stream ThreeD amp 0b FExtractor for ThreeD cout lt lt Enter A Y 4 values stream gt gt obj x gt gt obj y gt gt obj z return stream int main ThreeD a l 2 3 cout lt lt a cin gt gt a cout lt lt a return OQ A sample run is shown here 1 2 3 Enter X Y 4 values 5 6 7 5 6 7 Like inserters extractor functions cannot be members of the class they are designed to operate upon They can be friends or simply independent functions 9 C A Beginner s Guide by Herbert Schildt Except for the fact that you must return a reference to an object of type istream you can do anything you like inside an extractor function However for the sake of structure and clarity it is best to use extractors only for input operations Progress Check 1 What is an inserter adjustfield basefield boolalpha dec fixed floatfield hex internal left oct right scientific showbase s
446. or int j 2 j lt i j L amp 1 0 cout lt lt j lt lt cout lt lt yn return 0 of numbers Here is a portion of the output produced by the program OL 23 OF 3 of 4 2 OL Jl PaACLOrs PaClLors Factors Factors 34 C A Beginner s Guide by Herbert Schildt Factors OL Factors of CO N OD Factors of Factors Or OF 3 Factors Of 10 2 5 Factors of 11 F ctors of 472 2 3 4 Factors of 13 Factors of 14 2 7 Factors Of 152 3 5 Factors of 16 2 4 8 Factors of lis Factors Of 165 2 3 6 9 Factors of 19 Factors of 207 24 5 10 In the program the outer loop runs i from 2 through 100 The inner loop successively tests all numbers from 2 up toi printing those that evenly divide i CRITICAL SKILL 3 9 Using the goto Statement The goto is C s unconditional jump statement Thus when encountered program flow jumps to the location specified by the goto The statement fell out of favor with programmers many years ago because it encouraged the creation of spaghetti code However the goto is still occasionally and sometimes effectively used This book will not make a judgment regarding its validity as a form of program control It should be stated however that there are no programming situations that require the use of the goto statement it is not needed to make the language complete Rather it is a convenience which if used wisely can be of benefit in certain programmin
447. ose return 0 compare contents of buffers for i 0 i lt fl geount i if buf1 i buf2 1i cout lt lt Files differ n fl close f2 close return O while fl eof amp amp f2 e0f 4 r cout lt lt Files are the same n This code reads one buffer at a time from each of the files using the read function It then compares the contents of the buffers If the contents differ the files are closed the Files differ message is displayed and the program terminates Otherwise buffers continue to be read and compared until the end of one or both files is reached Because less than a full buffer may be read at the end of a file the program uses the gcount function to determine precisely how many characters are in the buffers If one of the files is shorter than the other the values returned by gcount will differ when the end of one of the files is reached In this case the message Files are of differing sizes will be displayed Finally if the files are the same then when the end of one file is reached the other will also have been reached This is confirmed by calling eof on each stream If the files compare equal in all regards then they are reported as equal 5 Finish the program by closing the files as shown here f1 close f2 close return O 6 The entire FileComp cpp program is shown here Project 11 1 Create a file comparison utility 4r l inc
448. ouble box double length double width double height return length width height Here is the output The volume is 373 296 One more point If a non void function returns because its closing curly brace is encountered an undefined that is unknown value is returned Because of a quirk in the formal C syntax a non void function need not actually execute a return statement This can happen if the end of the function is reached prior to a return statement being encountered However because the function is declared as returning a value a value will still be returned even though it is just a garbage value Of course good practice dictates that any non void function that you create should return a value via an explicit return statement CRITICAL SKILL 5 5 Using Functions in Expressions In the preceding example the value returned by box was assigned to a variable and then the value of this variable was displayed via a cout statement While not incorrect these programs could be written more efficiently by using the return value directly in the cout statement For example the main function in the preceding program can be written more efficiently like this 9 C A Beginner s Guide by Herbert Schildt int main f Use the return value of box use the return value of box directly directly in a cout statement cout lt lt The volume is lt lt box 10 1 11 2 3 3 lt return O When the cout sta
449. ould create a float variable using balance balance over_due Here over_due is a floating point variable of type balance which is another name for float Progress Check 1 An enumeration is a list of named constants 2 Enumerated values begin with what integer value 3 Show how to declare Bigint to be another name for long int CRITICAL SKILL 7 7 Bitwise Operators Since C is designed to allow full access to the computer s hardware it gives you the ability to operate directly upon the bits within a byte or word Toward this end C contains the bitwise operators Bitwise operations refer to the testing setting or shifting of the actual bits in a byte or word which correspond to C s character and integer types Bitwise operations cannot be used on bool float double long double void or other more complex data types Bitwise operations are important in a wide variety of systems level programming especially when status information from a device must be interrogated or constructed Table 7 1 lists the bitwise operators Each operator is examined in turn 16 C A Beginner s Guide by Herbert Schildt Operator Action amp AND OR A Exclusive OR XOR One s complement NOT gt gt Shift right lt lt Shift left Table 7 1 The Bitwise Operators AN D O R XO R and NOT the bitwise AND OR and one s complement NOT are governed by the same truth table as their logical equivalents except that th
450. out lt lt start n try start a try block Begin a try block cout lt lt Inside try block n throw 99 throw an error Throw an exception cout lt lt This will not execute catch int i catch an error Catch the exception cout lt lt Caught an exception value is cout lt lt i lt lt n cout lt lt end return This program displays the following output start Inside Ley block Caught an exception value is 99 end Look carefully at this program As you can see there is a try block containing three statements and a catch int i statement that processes an integer exception Within the try block only two of the three statements will execute the first cout statement and the throw Once an exception has been thrown control passes to the catch expression and the try block is terminated That is catch is not called 3 C A Beginner s Guide by Herbert Schildt Rather program execution is transferred to it The program s stack is automatically reset as necessary to accomplish this Thus the cout statement following the throw will never execute Usually the code within a catch statement attempts to remedy an error by taking appropriate action If the error can be fixed then execution will continue with the statements following the catch Otherwise program execution should be terminated in a controlled manner As me
451. out lt lt count 7 thie Statement will not execute This loop will never execute because its control variable count is greater than 5 when the loop is first entered This makes the conditional expression count lt 5 false from the outset thus not even one iteration of the loop will occur Some Variations on the for Loop The for is one of the most versatile statements in the C language because it allows a wide range of variations For example multiple loop control variables can be used Consider the following fragment of code LOr x Uy yalLU0 x lt yy 44x y Multiple loop control variables COUL lt R lt lt T T ec ya a s Here commas separate the two initialization statements and the two increment expressions This is necessary in order for the compiler to understand that there are two initialization and two increment statements In C the comma is an operator that essentially means do this and this Its most common use is in the for loop You can have any number of initialization and increment statements but in practice more than two or three make the for loop unwieldy Ask the Expert Q Does C support mathematical functions other than sqrt A Yes In addition to sqrt C supports an extensive set of mathematical library functions For example sin cos tan log pow ceil and floor are just a few If mathematical programming is your interest you will want to explore the C
452. ow void is used later in this book Progress Check 1 What is the primary difference between float and double 2 What values can a bool variable have To what Boolean value does zero convert 3 What is void Answer Key 1 The primary difference between float and double is in the magnitude of the values they can hold 2 Variables of type bool can be either true or false Zero converts to false 3 void is a type that stands for valueless Project 2 1 Talking to Mars At its closest point to Earth Mars is approximately 34 000 000 miles away Assuming there is someone on Mars that you want to talk with what is the delay between the time a radio signal leaves Earth and the time it arrives on Mars This project creates a program that answers this question Recall that radio signals travel at the speed of light approximately 186 000 miles per second Thus to compute the delay you will need to divide the distance by the speed of light Display the delay in terms of seconds and also in minutes Step by Step 1 Create a new file called Mars cpp 2 To compute the delay you will need to use floating point values Why Because the time interval will have a fractional component Here are the variables used by the program double distance 10 C A Beginner s Guide by Herbert Schildt double lightspeed double delay double delay in min Give distance and lightspeed initial values as shown here distance 34000000 0
453. pe of a literal if you like By default the C compiler fits an integer literal into the smallest compatible data type that will hold it beginning with int Therefore assuming 16 bit integers 10 is int by default but 103 000 is long Even though the value 10 could be fit into a char the compiler will not do this because it means crossing type boundaries By default floating point literals are assumed to be double Thus the value 123 23 is of type double For virtually all programs you will write as a beginner the compiler defaults are perfectly adequate In cases where the default assumption that C makes about a numeric literal is not what you want C allows you to specify the exact type of numeric literal by using a suffix For floating point types if you follow the number with an F the number is treated as a float If you follow it with an L the number becomes a long double For integer types the U suffix stands for unsigned and the L for long Both the U and the L must be used to specify an unsigned long Some examples are shown here 12 C A Beginner s Guide by Herbert Schildt Data Type Examples of Constants int 1 123 21000 234 long int 35000L 34L unsigned int 10000U 987U 40000U unsigned long 12323UL 900000UL Floett 123 23F 4 34e 3F double 23 23 123123 33 0 9876324 long double 1001 21 Hexadecimal and Octal Literals As you probably know in programming it is sometimes easier to use a number system base
454. pes At the core of the C type system are the seven basic data types shown here Type Meaning char Character wehar_t Wide character int Integer float Floating point double Double floating point bool Boolean void Valueless C allows certain of the basic types to have modifiers preceding them A modifier alters the meaning of the base type so that it more precisely fits the needs of various situations The data type modifiers are listed here signed unsigned long short The modifiers signed unsigned long and short can be applied to int The modifiers signed and unsigned can be applied to the char type The type double can be modified by long Table 2 1 shows all valid 2 C A Beginner s Guide by Herbert Schildt combinations of the basic types and the type modifiers The table also shows the guaranteed minimum range for each type as specified by the ANSI ISO C standard Type char unsigned char signed char int unsigned int signed int short int unsigned short int signed short int long int signed long int unsigned long int Flevest double long double Minimal Range 127 to 127 O to 255 127 to 127 32 767 to 32 767 O to 65 535 same as int 32 767 to 32 767 0 to 65 535 Same as short int 2 1 47 483 647 to 2 14 7 483 64 7 Same as long int 0 to 4 294 967 295 1E 37 to 1E 37 with six digits of precision 1E 37 to 1E 37 with ten digits of precision 1E 37 to 1E 37 with ten digits of
455. phism in C you can create one general set of stack routines that works for all three situations This way once you know how to use one stack you can use them all More generally the concept of polymorphism is often expressed by the phrase one interface multiple methods This means that it is possible to design a generic interface to a group of related activities Polymorphism helps reduce complexity by allowing the same interface to specify a general class of action It is the compiler s job to select the specific action that is method as it applies to each situation You the programmer don t need to do this selection manually You need only remember and utilize the general interface g C A Beginner s Guide by Herbert Schildt Inheritance Inheritance is the process by which one object can acquire the properties of another object This is important because it supports the concept of hierarchical classification If you think about it most knowledge is made manageable by hierarchical that is top down classifications For example a Red Delicious apple is part of the classification apple which in turn is part of the fruit class which is under the larger class food That is the food class possesses certain qualities edible nutritious and so on which also logically apply to its subclass fruit In addition to these qualities the fruit class has specific characteristics juicy sweet and so on that distinguish it f
456. previous object p gt show_num again show value of ob 0 return OQ The output from this program is 10 20 10 As you will see later in this book object pointers play a pivotal role in one of C s most important concepts polymorphism Progress Check 1 Can an array of objects be given initial values 2 Given a pointer to an object what operator is used to access a member Object References Objects can be referenced in the same way as any other data type No special restrictions or instructions apply Module 8 Mastery Check 1 What is the difference between a class and an object 2 What keyword is used to declare a class 36 C A Beginner s Guide by Herbert Schildt What does each object have its own copy of Show how to declare a class called Test that contains two private int variables called count and max What name does a constructor have What name does a destructor have Given this class declaration class Sample int i public Sample int x 1 x fi show how to declare a Sample object that initializes i to the value 10 When a member function is declared within a class declaration what optimization automatically takes place Create a class called Triangle that stores the length of the base and height of a right triangle in two private instance variables Include a constructor that sets these values Define two functions The first is hypot which returns the length of the hypotenuse
457. println bool displays either true or false when a Boolean value is output This illustrates how you can easily customize output to meet your own needs and tastes 5 Implement the print functions as shown next Here are the print void print bool b i1f b cout lt lt true else cout lt lt false void print int i cout lt lt i void print long i cout lt lt i void print char ch 22 functions C A Beginner s Guide by Herbert Schildt cout lt lt ch void print char str cout lt lt str void print double d cout lt lt d These functions are the same as their printlIn counterparts except that they do not output a newline Thus subsequent output appears on the same line 6 Here is the complete Print cpp program i Project 6 1 Create overloaded print and printin functions that display various types of data tf include lt iostream gt using namespace std These output a newline void println bool b void println int 1 void printlin long i void printin char ch void printin char str void printin double d These functions do not output a newline void print bool b void print int i void print long i void print char ch void print char str void print double d int main printin true 23 C A Beginner s Guide by Herbert Schildt printin 10 Th
458. ptimizing it as a register variable For this reason variables that control or are accessed within loops are good candidates for the register specifier Here is an example that uses register variables to improve the performance of the summation function which computes the summation of the values in an array This example assumes that only two variables will actually be optimized for speed Demonstrate register include lt iostream gt using namespace std int summation int nums int n int main int vals 1 2 3 4 5 int result result summation vals 5 cout lt lt Summation is lt lt result lt lt n return Return summation of an array of ints int summation int nums int n register int 1 a oe These variables are optimized for speed register int sum 0 for i 0 i lt n i sum sum nums i return sum Here the variable i which controls the for loop and sum which is accessed inside the loop are specified as register Since they are both used within the loop both benefit from being optimized for fast access This example assumed that only two variables could actually be optimized for speed so n and nums were not specified as register because they are not accessed as often as i and sum within the loop However in environments in which more than two variables can be optimized they too could be specified as register to further improve perform
459. r 12 Count uppercase letters include lt iostream gt include lt cstring gt include lt cctype gt using namespace std 9 C A Beginner s Guide by Herbert Schildt int main i char str 80 int i int count strepy str This Is A Test count Q for 1 0 str i i 1f isupper str i count cout lt lt str lt lt contains lt lt count lt lt uppercase letters return 0 13 Multiple indirection is the term used for the situation in which one pointer points to another 14 By convention a null pointer is assumed to be unused Module 5 Introducing Functions 1 The general form of a function is return type name parameter list j l i body of function j include lt iostream gt include lt cmath gt using namespace std double hypot double a double 5b int main 10 cout lt lt Hypotenuse of a 3 by 4 right triangle cout lt lt hypot 3 0 4 0 lt lt n return 0 C A Beginner s Guide by Herbert Schildt double hypot double a double b return sqrt a a b b 15 Yes a function can return a pointer No a function cannot return an array 16 Acustom version of strlen include lt iostream gt using namespace std int mystrlen char str int main cout lt lt Length of Hello There is cout lt lt mystrlen Hello There return 0 f A custom version of strlen int mys
460. r In Project 6 1 you created a collection of print and println functions To these functions adda second parameter that specifies an indentation level For example when print is called like this print test 18 output will indent 18 spaces and then will display the string test Have the indentation parameter default to 0 so that when it is not present no indentation occurs 9 Given this prototype bool myfunc char ch int a 10 int b 20 show the ways that myfunc can be called 10 Briefly explain how function overloading can introduce ambiguity 33 C A Beginner s Guide by Herbert Schildt Module 7 More Data Types and Operators Table of Contents CRITICAL SKILL 7 1 The const and volatile Qualifiers CRITICAL SKILL 7 2 extern CRITICAL SKILL 7 3 static Variables CRITICAL SKILL 7 4 register Variables CRITICAL SKILL 7 5 Enumerations CRITICAL SKILL 7 6 typedef CRITICAL SKILL 7 8 The Shift Operators CRITICAL SKILL 7 9 The Operator CRITICAL SKILL 7 10 The Comma Operator CRITICAL SKILL 7 11 Compound Assignment CRITICAL SKILL 7 12 Using sizeof This module returns to the topics of data types and operators In addition to the data types that you have been using so far C supports several others Some of these consist of modifiers added to the types you already know about Other data types include enumerations and typedefs C also provides several additional operators that greatly expand the range o
461. r constant that is one that is of type wchar_t is preceded with the character L For example wchar t wc wc L A 13 C A Beginner s Guide by Herbert Schildt Here wc is assigned the wide character constant equivalent of A You will not use wide characters often in your normal day to day programming but they are something that might be of importance if you need to internationalize your program Character Escape Sequences Enclosing character constants in single quotes works for most printing characters but a few characters such as the carriage return pose a special problem when a text editor is used In addition certain other characters such as the single and double quotes have special meaning in C so you cannot use them directly For these reasons C provides the character escape sequences sometimes referred to as backslash character constants shown in Table 2 3 so that you can enter them into a program As you can see the n that you have been using is one of the escape sequences Code Meaning b Backspace Wf Form feed n Newline r Carriage return t Horizontal tab Y Double quote Y Single quote character WA Backslash Ww Vertical tab a Alert N Octal constant where N is an octal constant xN Hexadecimal constant where N is a hexadecimal constant Table 2 3 The Character Escape Sequences Ask the Expert Q Is a string consisting of a single character the same as a character
462. r environments One last point Each C compiler specifies the range of the basic types in the header lt climits gt 7 C A Beginner s Guide by Herbert Schildt Floating Point Types Variables of the types float and double are employed either when a fractional component is required or when your application requires very large or small numbers The difference between a float and a double variable is the magnitude of the largest and smallest number that each one can hold Typically a double can store a number approximately ten times larger than a float Of the two double is the most commonly used One reason for this is that many of the math functions in the C function library use double values For example the sqrt function returns a double value that is the square root of its double argument Here sqrt is used to compute the length of the hypotenuse given the lengths of the two opposing sides F p5 r Use the Pythagorean theorem to find the length of the hypotenuse given the lengths of the two opposing sides x a include lt Lostream gt include lt cmath gt The lt cmathe header is needed for the sqrt function using namespace std int maini double x y x 5 0 y 4 0 z sqrt x x y y The sat function is part of C s math library cout lt lt Hypotenuse is lt lt return The output from the program is shown here Hypotenuse is 6 40312 One other point
463. r functions can be either members or nonmembers of a class Nonmember operator functions are often friend functions of the class however Although similar there are some differences between the way a member operator function is overloaded and the way a nonmember operator function is overloaded Each approach is described here 28 C A Beginner s Guide by Herbert Schildt NOTE Because C defines many operators the topic of operator overloading is quite large and it is not possible to describe every aspect of it in this book For a comprehensive description of operator overloading refer to my book C The Complete Reference Osborne McGraw Hill CRITICAL SKILL 9 10 Operator Overloading Using Member Functions To begin our examination of member operator functions let s start with a simple example The following program creates a class called ThreeD which maintains the coordinates of an object in three dimensional space This program overloads the and the operators relative to the ThreeD class Examine it closely Define and for the ThreeD class include lt iostream gt using namespace std class ThreeD int x Y Z 3 D coordinates public ThreeD x y 2 Q ThreeD int i int j int k x 1 y j z K ThreeD operator ThreeD op2 opl is implied ThreeD operator ThreeD op2 opl is implied void show rs Overload ThreeD ThreeD operator ThreeD op2 Overload
464. r in this fashion an object is created In other words an object is the device that supports encapsulation Ask the Expert Q have heard the term method applied to a subroutine Is a method the same as a function A In general the answer is yes The term method was popularized by Java What a C programmer calls a function a Java programmer calls a method C programmers also use the term method Because it is becoming so widely used sometimes the term method is also used when referring to a C 7 C A Beginner s Guide by Herbert Schildt Within an object code or data or both may be private to that object or public Private code or data is known to and accessible by only another part of the object That is private code or data cannot be accessed by a piece of the program that exists outside the object When code or data is public other parts of your program can access it even though it is defined within an object Typically the public parts of an object are used to provide a controlled interface to the private elements of the object C s basic unit of encapsulation is the class A class defines the form of an object It specifies both the data and the code that will operate on that data C uses a class specification to construct objects Objects are instances of a class Thus a class is essentially a set of plans that specifies how to build an object The code and data that constitute a class are called members of
465. r misuse pointers are a crucial part of C programming For example they allow C to support such things as linked lists and dynamic memory allocation They also provide one means by which a function can alter the contents of an argument However these and other uses of pointers will be discussed in subsequent modules In this module you will learn the basics about pointers and see how to manipulate them In a few places in the following discussions it is necessary to refer to the size of several of C s basic data types For the sake of discussion assume that characters are one byte in length integers are four bytes long floats are four bytes long and doubles have a length of eight bytes Thus we will be assuming a typical 32 bit environment What Are Pointers A pointer is an object that contains a memory address Very often this address is the location of another object such as a variable For example if x contains the address of y then x is said to point to y Pointer variables must be declared as such The general form of a pointer variable declaration is type var name Here type is the pointer s base type The base type determines what type of data the pointer will be pointing to var name is the name of the pointer variable For example to declare ip to be a pointer to an int use this declaration int ip Since the base type of ip is int it can be used to point to int values Here a float pointer is declare
466. r p is released using delete the destructor for each object in the array is executed as the output shows Also notice that because p is indexed as an array the dot operator is used to access members of Rectangle Progress Check 1 What operator allocates memory What operator releases memory 2 What happens if an allocation request cannot be fulfilled 3 Can memory be initialized when it is allocated CRITICAL SKILL 12 5 Namespaces Namespaces were briefly described in Module 1 Here they are examined in detail The purpose of a namespace is to localize the names of identifiers to avoid name collisions In the C programming environment there has been an explosion of variable function and class names Prior to the invention of namespaces all of these names competed for slots in the global namespace and many conflicts arose For example if your program defined a function called toupper it could depending upon its parameter list override the standard library function toupper because both names would be stored in the global namespace Name collision problems were compounded when two or more third party libraries were used by the same program In this case it was possible even likely that a name defined by one library would conflict with the same name defined by the other library The situation can be particularly troublesome for class names For example if your program defines a class call Stack and a library used by yo
467. r variable unique 2 What does typeid do 3 What type of object does typeid return CRITICAL SKILL 12 8 The Casting Operators C defines five casting operators The first is the traditional style cast described earlier in this book It has been part of C from the start The remaining four were added a few years ago They are dynamic_cast const_cast reinterpret_cast and static_cast These operators give you additional control over how casting takes place Each is examined briefly here dynamic_cast 49 C A Beginner s Guide by Herbert Schildt Perhaps the most important of the additional casting operators is the dynamic_cast The dynamic_cast performs a runtime cast that verifies the validity of a cast If at the time dynamic_cast is executed the cast is invalid then the cast fails The general form of dynamic_cast is shown here dynamic_cast lt target type gt expr Here target type specifies the target type of the cast and expr is the expression being cast into the new type The target type must be a pointer or reference type and the expression being cast must evaluate to a pointer or reference Thus dynamic_cast can be used to cast one type of pointer into another or one type of reference into another The purpose of dynamic_cast is to perform casts on polymorphic types For example given two polymorphic classes B and D with D derived from B a dynamic_cast can always cast a D pointer into a B pointer This is bec
468. r you use a built in function you must include its header In general there are two types of functions that will be used by your programs The first type is written by you and main is an example of this type of function Later you will learn how to write other functions of your own As you will see real world C programs contain many user written functions The second type of function is provided by the compiler The abs function used by the preceding program is an example Programs that you write will generally contain a mix of functions that you create and those supplied by the compiler When denoting functions in text this book has used and will continue to use a convention that has become common when writing about C A function will have parentheses after its name For example if a function s name is getval then it will be written getval when its name is used in a sentence This notation will help you distinguish variable names from function names in this book The C Libraries As just explained abs is provided with your C compiler This function and many others are found in the standard library We will be making use of library functions in the example programs throughout this book C defines a large set of functions that are contained in the standard function library These functions perform many commonly needed tasks including I O operations mathematical computations and 37 C A Beginner s Guide by
469. range will be at least 32 768 through 32 767 In C to declare a variable to be of type integer precede its name with the keyword int Later you will see that C supports a wide variety of built in variable types You can create your own data types too The second new feature is found in the next line of code length 7 this assigns 7 to length As the comment suggests this assigns the value 7 to length In C the assignment operator is the single equal sign It copies the value on its right side into the variable on its left After the assignment the variable length will contain the number 7 The following statement displays the value of length cout lt lt length This displays 7 In general if you want to display the value of a variable simply put it on the right side of lt lt in a cout statement In this specific case because length contains the number 7 it is this number that is displayed 16 C A Beginner s Guide by Herbert Schildt on the screen Before moving on you might want to try giving length other values and watching the results CRITICAL SKILL 1 6 Using an Operator Like most other computer languages C supports a full range of arithmetic operators that enable you to manipulate numeric values used in a program They include those shown here Addition Subtraction Multiplication f Division These operators work in C just like they do in algebra The following program u
470. rbert Schildt tinclude lt iostream gt include lt cstdlib gt using namespace std int main int i double avg val avg 0 0 for i O0 i lt S i f cout lt lt Enter a value cin gt gt val avg avg abs val avg avg 5 cout lt lt Average of absolute values lt lt avg return 0 Module 2 Introducing Data Types and Operators 1 The C integer types are int short int long int unsigned int unsigned short int unsigned long int signed int signed short int signed long int The type char can also be used as an integer type 2 12 2 is type double 3 A bool variable can be either true or false 4 The long integer type is long int or just long 5 The t sequence represents a tab The b rings the bell 6 True a string is surrounded by double quotes 7 The hexadecimal digits are O 1 2 3 4 5 6 7 8 9 A B C D E F 3 C A Beginner s Guide by Herbert Schildt 8 To initialize a variable use this general form type var value 9 The is the modulus operator It returns the remainder of an integer division It cannot be used on floating point values 10 When the increment operator precedes its operand C will perform the corresponding operation prior to obtaining the operand s value for use by the rest of the expression If the operator follows its operand then C will obtain the operand s value before incrementing 11 A C and E 12 x
471. rcpy style isosceles double area return getWidth getHeight 2 void showStyle cout lt lt Triangle is lt lt style lt lt n 23 C A Beginner s Guide by Herbert Schildt Extend Triangle class ColorTriangle public Triangle ColorTriangle inherits Triangle char color 20 which inherits TwoDShape public ColorTriangle char clr char style double w double h Triangle style w h strcpy color clr Display the color void showColor cout lt lt Color is i lt lt color lt lt yn int main f ColorTriangle t1 Blue right 8 0 12 0 ColorTriangle t2 Red isosceles 2 0 2 0 cout lt lt Info for t1 n tCl showstyle tl showDim Ci showColor cout lt lt Area is lt lt tl area lt lt n cout lt lt n cout lt lt Info for tz2 n t2 showstyle t2 showDim o A ColorTriangle object can call t2 showColor functions defined by itself and its cout lt lt Area is lt lt t2 area lt lt n base classes return The output of this program is shown here Info for tl Triangle is right Width and height are 8 and 12 Color is Blue Area is 48 Info for t2 Triangle is isosceles Width and height are 2 and 2 Color is Red Area is 2 Because of inheritance ColorTriangle can make use of the previously defined classes of Triangle and TwoDShape adding
472. re second call to display n display a cout lt lt After display returns n n return 0 11 C A Beginner s Guide by Herbert Schildt The following output is produced Before constructing a Inside constructor After constructing a Before call to display 10 Destructing After display returns Before call to mkBigger Inside constructor Destructing Destructing _ _ _ _ _ _ o oOOO Notice the second Destructing After mkBigger returns Message Before second call to display 20 Destructing After display returns Destructing In this example mkBigger creates a local object called o that has a val value twice that of the invoking object This object is then returned by the function and assigned to a inside main Then o is destroyed causing the first Destructing message to be displayed But what explains the second call to the destructor When an object is returned by a function a temporary object is automatically created which holds the return value It is this object that is actually returned by the function After the value has been returned this object is destroyed This is why the output shows a second Destructing message just before the message After mkBigger returns This is the temporary object being destroyed As was the case when passing an object to a function there is a potential problem when returning an object from a function
473. re the extra parentheses needed by most function like macros However function like macros will almost certainly continue to be a part of C programs for some time to come because many former C programmers continue to use them out of habit error When the error directive is encountered it forces the compiler to stop compilation This directive is used primarily for debugging The general form of the directive is error error message 4 C A Beginner s Guide by Herbert Schildt Notice that the error message is not between double quotes When the compiler encounters this directive it displays the error message and other information and terminates compilation Your implementation determines what information will actually be displayed You might want to experiment with your compiler to see what is displayed include The include preprocessor directive instructs the compiler to include either a standard header or another source file into the file that contains the include directive The name of a standard header should be enclosed between angle brackets as shown in the programs throughout this book For example include lt fstream gt includes the standard header for file I O When including another source file its name can be enclosed between double quotes or angle brackets For example the following two directives both instruct C to read and compile a file called sample h include lt sample h gt include sample h
474. report several types of warning messages Error messages report things that are unequivocally wrong in your program such as forgetting a semicolon Warnings point out suspicious but technically correct code You the 14 C A Beginner s Guide by Herbert Schildt programmer then decide whether the suspicion is justified Warnings are also used to report such things as inefficient constructs or the use of obsolete features Generally you can select the specific type of warnings that you want to see The programs in this book are in compliance with Standard C and when entered correctly they will not generate any troublesome warning messages For the examples in this book you will want to use your compiler s default or normal error reporting However you should examine your compiler s documentation to see what options you have at your disposal Many compilers have sophisticated features that can help you spot subtle errors before they become big problems Understanding your compiler s error reporting system is worth your time and effort Progress Check 1 Where does a C program begin execution 2 What is cout 3 What does include lt iostream gt do Answer Key 1 A C program begins execution with main 2 coutis a predefined identifier that is linked to console output 3 Itincludes the header lt iostream gt which supports I O CRITICAL SKILL 1 5 A Second Simple Program
475. returns a reference to a double double amp f i return val return reference to val This returns a reference to the global variable val 9 C A Beginner s Guide by Herbert Schildt The output of this program is shown here 100 100 99 1 Let s examine this program closely At the beginning f is declared as returning a reference to a double and the global variable val is initialized to 100 In main the following statement displays the original value of val cout lt lt f lt lt n display val s value When f is called it returns a reference to val using this return statement return val return reference to val This statement automatically returns a reference to val rather than val s value This reference is then used by the cout statement to display val s value In the line x f assign value of val to x the reference to val returned by f assigns the value of val to x The most interesting line in the program is shown here f 99 1 change val s value This statement causes the value of val to be changed to 99 1 Here is why since f returns a reference to val this reference becomes the target of the assignment statement Thus the value of 99 1 is assigned to val indirectly through the reference to it returned by f Here is another sample program that uses a reference return type 10 C A Beginner s Guide by Herbert Schildt Return a reference to an
476. riginal array 1s n ms for t 0 t lt size t cout lt lt nums t lt lt cout lt lt n This is the bubble sort for a l a lt size a for b size 1 b gt a b 1f nums b 1 gt nums b if out of order exchange elements t nums b 1 nums b 1 nums b nums b t display sorted array cout lt lt nSorted array 1s n ns for t 0 t lt size t cout lt lt nums t lt lt return Q The output is shown here Original array is 41 18467 6334 26500 19169 15724 11478 29358 26962 24464 Sorted array is 41 6334 11478 15724 18467 19169 24464 26500 26962 29358 Although the bubble sort is good for small arrays it is not efficient when used on larger ones The best general purpose sorting algorithm is the Quicksort The Quicksort however relies on features of C that you have not yet learned Also the C standard library contains a function 10 C A Beginner s Guide by Herbert Schildt called qsort that implements a version of the Quicksort but to use it you will also need to know more about C CRITICAL SKILL 4 4 Strings By far the most common use for one dimensional arrays is to create character strings C supports two types of strings The first and most commonly used is the null terminated string which is a null terminated character array A null is zero Thus a null terminated string contains the characters that make up the string followed by a null Null
477. rite the main function from Project 3 3 so that it uses the new Help class The entire listing for HelpClass cpp is shown here i Project 8 1 Convert the Help system from Project 3 3 into a Help class a include lt iostream gt using namespace std A class that encapsulates a help system class He public lp void helpon char what void showmenu bool isvalid char ch Display help information void Help helpon char what swiltch what Case 12 L C A Beginner s Guide by Herbert Schildt cout lt lt cout lt lt cout lt lt break taza lt lt case cout cout lt lt The if n n 1f condition statement n alse statement n The switch n n switch expression n cout lt lt case constant n cout lt lt statement sequence n cout lt lt break n cout lt lt an cout lt lt n break case 3 cout lt lt The for n n cout lt lt for init condition increment cout lt lt statement n break case d cout lt lt The while n n cout lt lt while condition statement n break case 5 cout lt lt The do while n n cout lt lt do n cout lt lt statement n cout lt lt while condition n break case 6 cout lt lt The break n n cout lt lt break n break case J cout lt lt The continue
478. rom other food The apple class defines those qualities specific to an apple grows on trees not tropical and so on A Red Delicious apple would in turn inherit all the qualities of all preceding classes and would define only those qualities that make it unique Without the use of hierarchies each object would have to explicitly define all of its characteristics Using inheritance an object need only define those qualities that make it unique within its class It can inherit its general attributes from its parent Thus it is the inheritance mechanism that makes it possible for one object to be a specific instance of a more general case Progress Check 1 Name the principles of OOP 2 What is the basic unit of encapsulation in C 3 What is the commonly used term for a subroutine in C Answer Key 1 Encapsulation polymorphism and inheritance are the principles of OOP 2 The class is the basic unit of encapsulation in C 3 Function is the commonly used term for a subroutine in C Ask the Expert Q You state that object oriented programming OOP is an effective way to manage large programs However it seems that OOP might add substantial overhead to relatively small ones As it relates to C 9 C A Beginner s Guide by Herbert Schildt is this true A No A key point to understand about C is that it allows you to write object oriented programs but does not require you to do so This is one of the
479. ror Which version of mytune should return 0 this use float myfunc float i return 1 double myfunc double i return 1 Here myfunc is overloaded so that it can take arguments of either type float or type double In the unambiguous line myfunc double is called because unless explicitly specified as float all floating point constants in C are automatically of type double However when myfunc is called using the integer 10 ambiguity is introduced because the compiler has no way of knowing whether it should be converted to a float or to a double Both are valid conversions This confusion causes an error message to be displayed and prevents the program from compiling 30 C A Beginner s Guide by Herbert Schildt The central issue illustrated by the preceding example is that it is not the overloading of myfunc relative to double and float that causes the ambiguity Rather the confusion is caused by the specific call to myfunc using an indeterminate type of argument Put differently it is not the overloading of myfunc that is in error but the specific invocation Here is another example of ambiguity caused by the automatic type conversions in C Another example of overloading ambiguity include lt iostream gt using namespace std char myfunc unsigned char ch char myfunc char ch int main cout lt lt myfunc c this calls myfunc char cout
480. s an operator a cast is unary and has the same precedence as any other unary operator 27 C A Beginner s Guide by Herbert Schildt There are times when a cast can be very useful For example you may wish to use an integer for loop control but also perform computation on it that requires a fractional part as in the program shown here yf ii Demenstrate a cast include lt iostream gt using namespace std int maini int i The cast to float causes a fractional component ta be displayed for i 1l 1 lt 10 i m i I F lt lt float 1 2 lt lt n cout lt lt 1 lt lt 2 is return O Here is the output from this program if 2 ast 0 5 2 2 is 1 3 2 1er 135 ay 2 AS 2 57 2 18 2x5 67 2182 3 ty 2 iD B55 8 2 is 4 Of 2 16 4 5 Loy 2 ae 5 Without the cast float in this example only an integer division would be performed The cast ensures that the fractional part of the answer will be displayed CRITICAL SKILL 2 11 Spacing and Parentheses An expression in C can have tabs and spaces in it to make it more readable For example the following two expressions are the same but the second is easier to read x 10 y 127 x x 10 7 y 127 x Parentheses increase the precedence of the operations contained within them just like in algebra Use of redundant or additional parentheses will not cause errors or slow down the execution of the expression You are encouraged to
481. s but that can still be inherited and accessed by a derived class The protected specifier can also be used with structures Consider this sample program Demonstrate protected members tinclude lt iostream gt using namespace std Here i and j are protected class E protected a int i j private to B but accessible to D public void set int a int b 1 a j b void show cout lt lt i lt lt lt lt j lt lt n class D public B int k public D may access B s i and j D can access i and because void setk k i j they are protected not private void showk cout lt lt k lt lt n Fi int mair D ob ob set 2 3 OK set is public in B ob show OK show is public B ob setk ob showk return 0 Here because B is inherited by D as public and because i and j are declared as protected D s function setk can access them If i and j were declared as private by B then D would not have access to them and the program would not compile When a base class is inherited as public protected members of the base class become protected members of the derived class When a base class is inherited as private protected members of the base class become private members of the derived class 10 C A Beginner s Guide by Herbert Schildt The protected access specifier may occur anywhere in a class declaration although typicall
482. s terminating because of some error return is one of C s keywords and it is used to return a value from a function All of your programs should return O when they terminate normally that is without error The closing curly brace at the end of the program formally concludes the program Handling Syntax Errors If you have not yet done so enter compile and run the preceding program As you may know from previous programming experience it is quite easy to accidentally type something incorrectly when entering code into your computer Fortunately if you enter something incorrectly into your program the compiler will report a syntax error message when it tries to compile it Most C compilers attempt to make sense out of your source code no matter what you have written For this reason the error that is reported may not always reflect the actual cause of the problem In the preceding program for example an accidental omission of the opening curly brace after main may cause the compiler to report the cout statement as the source of a syntax error When you receive syntax error messages be prepared to look at the last few lines of code in your program in order to find the error Ask the Expert Q In addition to error messages my compiler offers several types of warning messages How do warnings differ from errors and what type of reporting should use A In addition to reporting fatal syntax errors most C compilers can also
483. s that are the same A switch statement is usually more efficient than nested ifs 7 C A Beginner s Guide by Herbert Schildt The statement sequences associated with each case are not blocks However the entire switch statement does define a block The importance of this will become apparent as you learn more about C The following program demonstrates the switch It asks for a number between 1 and 3 inclusive It then displays a proverb linked to that number Any other number causes an error message to be displayed j A simple proverb generator that demonstrates the switch 7 include lt iostream gt using namespace std int main int num cout lt lt Enter a number from 1 to 3 cin gt gt num switch num The value of num determines the case sequence executed case l cout lt lt A rolling stone gathers no moss n break case 2 cout lt lt A bird in hand is worth two in the bush n break case 3 cout lt lt A fool and his money are soon parted n break default cout lt lt You must enter either 1 2 or 3 n return 0 Here are two sample runs Enter a number from 1 to 3 1 A rolling stone gathers no moss Enter a number from 1 to 3 5 You must enter either 1 2 or 3 Technically the break statement is optional although most applications of the switch will use it When encountered within the statement sequence of a case the break statement
484. same as the previous version Again notice that by making x and y reference parameters there is no need to use the operator when exchanging values Remember the compiler automatically generates the addresses of the arguments used to call swap and automatically dereferences x and y Let s review When you create a reference parameter that parameter automatically refers to that is implicitly points to the argument used to call the function Further there is no need to apply the amp operator to an argument Also inside the function the reference parameter is used directly the operator is not used All operations involving the reference parameter automatically refer to the argument used in the call to the function Finally when you assign a value to a reference parameter you are actually assigning that value to the variable to which the reference is pointing In the case of a function parameter this will be the variable used in the call to the function One last point The C language does not support references Thus the only way to create a call by reference in C is to use pointers as shown earlier in the first version of swap When converting C code to C you will want to convert these types of parameters to references where feasible 7 C A Beginner s Guide by Herbert Schildt Ask the Expert Q In some C code have seen a declaration style in which the amp is associated with the type name as shown here
485. se cout lt lt Access denied n return 0 9 True A prototype prevents a function from being called with the improper number of arguments 10 include lt iostream gt using namespace std void printnum int n int main printnum 10 return 0 void printnum int n 1f n gt 1 printnum n 1 Cout lt lt n lt lt Module 6 A Closer Look at Functions 1 An argument can be passed to a subroutine using call by value or call by reference 13 C A Beginner s Guide by Herbert Schildt A reference is an implicit pointer A reference parameter is created by preceding the parameter name with an amp f ch amp i include lt iostream gt include lt cmath gt using namespace std void round double amp num int main l double i 100 4 cout lt lt i lt lt rounded is round 1 cout lt lt 1 lt lt n 1 10 9 cout lt lt i lt lt rounded is round 1 cout lt lt i lt lt n return 0 void round double amp num double frac double val decompose num into whole and fractional parts frac modf num amp val if frac lt 0 5 num val else num val 1 0 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std Swap args and return minimum int amp min_swap int amp x int amp y int main int i Jj min i 10 j 20 cout lt lt Initial values of i
486. se operations either The C Predefined Streams C contains several predefined streams that are automatically opened when your C program begins execution They are cin cout cerr and clog As you know cin is the stream associated with standard input and cout is the stream associated with standard output The cerr stream is linked to standard output and so is clog The difference between these two streams is that clog is buffered but cerr is not This means that any output sent to cerr is immediately output but output to clog is written only when a buffer is full Typically cerr and clog are streams to which program debugging or error information is written C also opens wide 16 bit character versions of the standard streams called wcin wcout wcerr and wclog These streams exist to support languages such as Chinese that require large character sets We won t be using them in this book By default the C standard streams are linked to the console but they can be redirected to other devices or files by your program They can also be redirected by the operating system CRITICAL SKILL 11 2 The C Stream Classes As you learned in Module 1 C provides support for its I O system in lt iostream gt Inthis header a rather complicated set of class hierarchies is defined that supports I O operations The I O classes begin with a system of template classes As you will learn in Module 12 a template defines the form of a class witho
487. se it without fear of side effects For an example of global g C A Beginner s Guide by Herbert Schildt static variables we will rework the running average program from the preceding section In this version the program is broken into the two files shown here The function reset which resets the average is also added include lt iostream gt using namespace std int running_avg int i void reset int maini int num do cout lt lt Enter numbers 1 to quit 2 to reset cin gt gt num if num 2 reset continue if num 1 cout lt lt Running average is lt lt running_avg num cout lt lt n while num 1 return 0 Ef ennnen Second File static int sum 0 count 0 These are known only in the file in which they are declared int running_avg int i sum sum 1 count return sum count void reset sum Q count Here sum and count are now global static variables that are restricted to the second file Thus they can be accessed by both running _avg and reset in the second file but not elsewhere This allows them 9 C A Beginner s Guide by Herbert Schildt to be reset by a call to reset so that a second set of numbers can be averaged When you run the program you can reset the average by entering 2 However no functions outside the second file can access those variab
488. sed is the default argument In C you can give a parameter a default value that is automatically used when no argument corresponding to that parameter is specified in a call to a function Default arguments can be used to simplify calls to complex functions Also they can sometimes be used as a shorthand form of function overloading A default argument is specified in a manner syntactically similar to a variable initialization Consider the following example which declares myfunc as taking two int arguments The first defaults to 0 The second defaults to 100 void myfunc int x 0 int y 100 Now myfunc can be called by one of the three methods shown here myfunc 1 2 pass explicit values myfunc 10 pass x a value let y default myfunc let both x and y default The first call passes the value 1 to x and 2 to y The second gives x the value 10 and allows y to default to 100 Finally the third call causes both x and y to default The following program Demonstrate default arguments include lt iostream gt using namespace std void myfunc int x 0 int y 100 myfunc specifies default arguments for int main aah a myfunc l 2 myfune 10 my func return void myfunc int x int y COU ca Mara iL ra a ra n y i n ra y ra r n r The output shown here confirms the use of the default arguments 1 y 2 26 C A Beginner s Guide by Herbert Schildt 10
489. ses For example assume some function named MyFunc To call MyFunc you would write 35 C A Beginner s Guide by Herbert Schildt Myron 7 When a function is called program control is transferred to that function and the code contained within the function is executed When the function s code ends control is transferred back to the caller Thus a function performs a task for other parts of a program Some functions require one or more arguments which you pass when the function is called Thus an argument is a value passed to a function Arguments are specified between the opening and closing parentheses when a function is called For example if MyFunc requires an integer argument then the following calls MyFunc with the value 2 Myrhane 2 When there are two or more arguments they are separated by commas In this book the term argument list will refer to comma separated arguments Remember not all functions require arguments When no argument is needed the parentheses are empty A function can return a value to the calling code Not all functions return values but many do The value returned by a function can be assigned to a variable in the calling code by placing the call to the function on the right side of an assignment statement For example if MyFunc returned a value it could be called as shown here x MyFunc 2 This statement works as follows First MyFunc is called When it returns its ret
490. ses the operator to compute the area of a rectangle given its length and the width Using an operator inelude lt Lostream gt using namespace std int maint int length this declares a variable int width this declares another variable int area Ji this does too length 7 this assigns 7 to length width 5 this assigns 5 to width area length width compute area lt Assign the product of length and width te area cout lt lt The area is cout lt lt area This displays 35 return OU This program declares three variables length width and area It assigns the value 7 to length and the value 5 to width It then computes the product and assigns that value to area The program outputs the following The area is 35 17 C A Beginner s Guide by Herbert Schildt In this program there is actually no need for the variable area For example the program can be rewritten like this ii BR simplified version of the area program include lt Lostream gt using namespace sted int maint int length this declares a variable int width ii this declares another variable i length 7 this assigns 7 to length width 5 Z this assigns 5 to width cout lt lt The area is eout lt lt length width This displays 35 4 Output length width directly return In this version the area is computed in the cout statement by multiplying l
491. single functional unit that performs clearly delineated actions Thus you will want your classes to be as small as possible but no smaller That is classes that contain extraneous functionality confuse and destructure code but classes that contain too little functionality are fragmented What is the balance It is at this point that the science of programming becomes the art of programming Fortunately most programmers find that this balancing act becomes easier with experience To begin gaining that experience you will convert the help system from Project 3 3 in Module 3 into a Help class Let s examine why this is a good idea First the help system defines one logical unit It simply displays the syntax for the C control statements Thus its functionality is compact and well defined Second putting help in a class is an esthetically pleasing approach Whenever you want to offer the help 9 C A Beginner s Guide by Herbert Schildt system to a user simply instantiate a help system object Finally because help is encapsulated it can be upgraded or changed without causing unwanted side effects in the programs that use it Step by Step 1 Create a new file called HelpClass cpp To save you some typing you might want to copy the file from Project 3 3 Help3 cpp into HelpClass cpp 2 To convert the help system into a class you must first determine precisely what constitutes the help system For example in Help3 cpp there is c
492. situations such as debugging it is not usually appropriate You may have functions that must be overridden by the derived class in order for the derived class to have any meaning Consider the class Triangle It has no meaning if area is not defined In this case you want some way to ensure that a derived class does indeed override all necessary functions The C solution to this problem is the pure virtual function A pure virtual function is a function declared in a base class that has no definition relative to the base As a result any derived class must define its own version it cannot simply use the version defined in the base To declare a pure virtual function use this general form virtual type func name parameter list 0 Here type is the return type of the function and func name is the name of the function Using a pure virtual function you can improve the TwoDShape class Since there is no meaningful concept of area for an undefined two dimensional figure the following version of the preceding program declares area as a pure virtual function inside TwoDShape This of course means that all classes derived from TwoDShape must override area Use a pure virtual function tinclude lt iostream gt include lt cstring gt using namespace std A class for two dimensional objects class TwoDShape these are private double width double height add a name field char name 20 public D
493. some types of algorithms In this project you will see an example The program developed here reverses the contents of a string in place Thus instead of copying the string back to front into another array it reverses the contents of the string inside the array that holds it The program uses two pointer variables to accomplish this One initially points to the beginning of a string and the other initially points to the last character in the string A loop is set up that continues to run as long as the start pointer is less than the end pointer Each time through the loop the characters pointed to by the pointers are swapped and the pointers are advanced When the start pointer is greater than or equal to the end pointer the string has been reversed 34 C A Beginner s Guide by Herbert Schildt Step by Step 1 Create a file called StrRev cpp 2 Begin by adding these lines to the file Fi w Project 4 2 Reverse a string in place include lt iostream gt include lt cstring gt using namespace std int main char str this is a test char start end int len char t The string to be reversed is contained in str The pointers start and end will be used to access the string 3 Add these lines which display the original string obtain the string s length and set the initial values for the start and end pointers cout lt lt Original lt lt str lt lt n len strlen str start str en
494. ss 37 C A Beginner s Guide by Herbert Schildt Use friend operator functions include lt iostream gt using namespace std class ThreeD int x y Z 3 D coordinates public ThreeD x y z 0 ThreeD int i int jJ int k x 1 y j z K friend ThreeD operator ThreeD opl ThreeD op2 void show Here operator is a friend 3 of ThreeD Notice that two parameters are required The is now a friend function ThreeD operator ThreeD opl ThreeD op2 ThreeD temp temp x opl x op2 x temp y opl y op2 y temp z2 opl z op2 z return temp Show X Y 4 coordinates void ThreeD show cout lt lt x lt lt cout lt lt y lt lt T 38 C A Beginner s Guide by Herbert Schildt cout lt lt z lt lt n int main ThreeD a l 2 3 b 10 10 10 c cout lt lt Original value of a a show cout lt lt Original value of b b show cout lt lt n c a b adda and b together cout lt lt Value of c after c a b c show cout lt lt yn ec a b e adda b and e together cout lt lt Value of c after a b c c show cout lt lt n c be a demonstrate multiple assignment cout lt lt Value of c after c b a c show cout lt lt Value of b after c b a b show return 0 The output is shown here Original value of a
495. ss Check 1 What are the main differences between local and global variables 2 Cana local variable be declared anywhere within a block 3 Doesa local variable hold its value between calls to the function in which it is declared CRITICAL SKILL 5 8 Passing Pointers and Arrays to Functions The preceding examples have used simple values such as int or double as arguments However there will be times when you will want to use pointers and arrays as arguments While passing these types of arguments is straightforward some special issues need to be addressed Passing a Pointer 18 C A Beginner s Guide by Herbert Schildt To pass a pointer as an argument you must declare the parameter as a pointer type Here is an example Pass a pointer to a function include lt iostream gt using namespace std f takes an int pointer as a parameter void f int j declares a pointer parameter int main int i int p p amp 1 p now points fip pass a pointer cout lt lt i 1 is now return 0 receives a pointer void f int j to i is called with a pointer to an integer 100 to an int j 100 var pointed to by j is assigned 100 Study this program carefully As you can see f takes one parameter an int pointer Inside main p an int pointer is assigned the address of i Next f is called with p as an argument When the pointer
496. ssign return value cout lt lt The volume is lt lt answer return QO This function returns a value int box int length int width int height return length width height Return the volume Here is the output The volume is 330 In this example box returns the value of length width height using the return statement This value is then assigned to answer That is the value returned by the return statement becomes box s value in the calling routine Since box now returns a value it is not preceded by the keyword void Remember void is only used when a function does not return a value Instead box is declared as returning a value of type int Notice that the return type of a function precedes its name in both its prototype and its definition Of course int is not the only type of data a function can return As stated earlier a function can return any type of data except an array For example the following program reworks box so that it takes double parameters and returns a double value g C A Beginner s Guide by Herbert Schildt Returning a double value include lt iostream gt using namespace std use double data double box double length double width double height int maini double answer answer box 10 1 11 2 3 3 assign return value cout lt lt The volume is lt lt answer return 0 This version of box uses double data d
497. ssor operators and These operators are used in conjunction with define The operator causes the argument it precedes to become a quoted string For example consider this program 9 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std define mkstr s s int main cout lt lt mkstr I like C return 0 The C preprocessor turns the line cout lt lt mkstr I like C into cout lt lt I like C The operator is used to concatenate two tokens Here is an example include lt iostream gt using namespace std define concat a b a b int main int xy 10 cout lt lt concat x y return 0 The preprocessor transforms cout lt lt concat x y into cout lt lt xy If these operators seem strange to you keep in mind that they are not needed or used in most programs They exist primarily to allow some special cases to be handled by the preprocessor Predefined Macro Names C specifies six built in predefined macro names They are 10 C A Beginner s Guide by Herbert Schildt _ LINE FILE DATE TIME STDC cplusplus The __LINE_ and__FILE___ macros were described in the discussion of line Briefly they contain the current line number and filename of the program when it is being compiled The __DATE__ macro contains a string of the form month day year that is the date of the translation of th
498. statement do 29 C A Beginner s Guide by Herbert Schildt 2 What does the for statement do 3 What are C s relational operators Answer Key 1 if is C s conditional statement 2 The for is one of C s loop statements 3 The relational operators are lt gt lt and gt CRITICAL SKILL 1 9 Using Blocks of Code Another key element of C is the code block A code block is a grouping of two or more statements This is done by enclosing the statements between opening and closing curly braces Once a block of code has been created it becomes a logical unit that can be used any place that a single statement can For example a block can be a target of the if and for statements Consider this if statement Here if w is less than h then both statements inside the block will be executed Thus the two statements inside the block form a logical unit and one statement cannot execute without the other also executing The key point here is that whenever you need to logically link two or more statements you do so by creating a block Code blocks allow many algorithms to be implemented with greater clarity and efficiency Here is a program that uses a block of code to prevent a division by zero 30 C A Beginner s Guide by Herbert Schildt F Demonstrate a block of code include lt iostream gt using namespace std int maing double result n d cout lt lt Enter valu
499. stead strings are implemented as arrays of characters This approach to strings allows greater power and flexibility than are available in languages that use a distinct string type A pointer is an object that contains a memory address Typically a pointer is used to access the value of another object Often this other object is an array In fact pointers and arrays are related to each other more than you might expect 1 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 4 1 Use one dimensional arrays A one dimensional array is a list of related variables Such lists are common in programming For example you might use a one dimensional array to store the account numbers of the active users on a network Another array might store the current batting averages for a baseball team When computing the average of a list of values you will often use an array to hold the values Arrays are fundamental to modern programming The general form of a one dimensional array declaration is type name size Here type declares the base type of the array The base type determines the data type of each element that makes up the array The number of elements the array can hold is specified by size For example the following declares an integer array named sample that is ten elements long int sample 10 An individual element within an array is accessed through an index An index describes the position of an element within an array In C a
500. struct then public is the default Let s examine the ramifications of using public or private access The protected specifier is described in the next section Ask the Expert Q have heard the terms superclass and subclass used in discussions of Java programming Do these terms have meaning in C A What Java calls a superclass C calls a base class What Java calls a subclass C calls a derived class You will commonly hear both sets of terms applied to a class of either language but this book will 7 C A Beginner s Guide by Herbert Schildt continue to use the standard C terms By the way C also uses the base class derived class terminology When a base class is inherited as public all public members of the base class become public members of the derived class In all cases the private elements of the base class remain private to that class and are not accessible by members of the derived class For example in the following program the public members of B become public members of D Thus they are accessible by other parts of the program Demonstrate public inheritance include lt iostream gt using namespace std class E int i j public void set int a int b i a j b lt lt j lt lt n void show cout lt lt i lt lt rf class D public B Here Bis inherited as public int k public Diint x k x void showk cout lt lt k lt
501. t function By using a default argument for len it is possible to combine both operations into one function As this example illustrates default arguments sometimes provide a shorthand form of function overloading Using Default Arguments Correctly Although default arguments are a powerful tool when used correctly they can also be misused The point of default arguments is to allow a function to perform its job in an efficient easy to use manner while still allowing considerable flexibility Toward this end all default arguments should reflect the way a function is generally used or a reasonable alternate usage When there is no single value that is normally associated with a parameter then there is no reason to declare a default argument In fact declaring default arguments when there is insufficient basis for doing so destructures your code because they are liable to mislead and confuse anyone reading your program Finally a default argument should cause no harm That is the accidental use of a default argument should not have irreversible negative consequences For example forgetting to specify an argument should not cause an important data file to be erased Progress Check 1 Show how to declare a void function called count that takes two int parameters called a and b and give each a default value of 0 2 Can default arguments be declared in both a function s prototype and its definition 3 Is this declaration corre
502. t void swapargs lt int gt int amp a int amp b int temp temp a a b b temp cout lt lt Inside swapargs int specialization n As you can see the new style syntax uses the template lt gt construct to indicate specialization The type of data for which the specialization is being created is placed inside the angle brackets following the function name This same syntax is used to specialize any type of generic function While there is no advantage to using one specialization syntax over the other at this time the new style syntax is probably a better approach for the long term Explicit specialization of a template allows you to tailor a version of a generic function to accommodate a unique situation perhaps to take advantage of some performance boost that applies to only one type of data for example However as a general rule if you need to have different versions of a function for different data types you should use overloaded functions rather than templates CRITICAL SKILL 12 3 Generic Classes In addition to using generic functions you can also define a generic class When you do this you create a class that defines all the algorithms used by that class however the actual type of data being manipulated will be specified as a parameter when objects of that class are created Generic classes are useful when a class uses logic that can be generalized For example the same algorithm that maintains a qu
503. t can be included in an I O expression The standard manipulators are shown in Table 11 1 To use those manipulators that take arguments you must include lt iomanip gt in your program Manipulator Purpose Input Output boolalpha Turns on boolalpha flag Input Output dec Turns on dec flag Input Output andi ral a newline character and flushes the Output ends Outputs a null Output fixed Turns on fixed flag Output flush Flushes a stream Output hex Turns on hex flag Input Output internal Turns on internal flag Output left Turns on left flag Output noboolalpha Turns off boolalpha flag Input Output noshowbase Turns off showbase flag Output noshowpoint Turns off showpoint flag Output noshowpos Turns off showpos flag Output noskipws Turns off skipws flag Input nounitbuf Turns off unitbuf flag Output nouppercase Turns off uppercase flag Output oct Turns on oct flag Input Output resetiosflags fmtflags f Turns off the flags specified in f Input Output right Turns on right flag Output scientific Turns on scientific flag Output setbase int base Sets the number base to base Input Output setfill int ch Sets the fill character to ch Output setiosflags fmtflags f Turns on the flags specified in f Input Output setprecision int p Sets the number of digits of precision Output setw int w Sets the field width to w Output showbase Turns on showbase flag Output showp
504. t common application of this is found in function parameters A base class reference parameter can receive objects of the base class as well as any other type derived from that base CRITICAL SKILL 10 9 Virtual Functions and Polymorphism The foundation upon which C builds its support for polymorphism consists of inheritance and base class pointers The specific feature that actually implements polymorphism is the virtual function The remainder of this module examines this important feature Virtual Function Fundamentals A virtual function is a function that is declared as virtual in a base class and redefined in one or more derived classes Thus each derived class can have its own version of a virtual function What makes virtual functions interesting is what happens when a base class pointer is used to call one When a virtual function is called through a base class pointer C determines which version of that function to call based upon the type of the object pointed to by the pointer This determination is made at runtime Thus when different objects are pointed to different versions of the virtual function are executed In other words it is the type of the object being pointed to not the type of the pointer that determines which version of the virtual function will be executed Therefore if a base class contains a virtual function and if two or more different classes are derived from that base class then when different types of obje
505. t defined by ASCII The extended characters if they exist often include special characters such as foreign language symbols and scientific notations The ASCII characters use values that are less than 128 The extended character set begins at 128 and continues to 255 This program prints all characters between 32 which is a space and 255 When you run this program you will most likely see some very interesting characters This program displays all printable characters including the extended character set if one exists ii include lt iostream gt using namespace std int main unsigned char ch ch 32 while ch Use a while loop cout lt lt ch ch return 0 Examine the loop expression in the preceding program You might be wondering why only ch is used to control the while Since ch is an unsigned character it can only hold the values O through 255 When it holds the value 255 and is then incremented its value will wrap around to zero Therefore the test for ch being zero serves as a convenient stopping condition As with the for loop the while checks the conditional expression at the top of the loop which means that the loop code may not execute at all This eliminates the need to perform a separate test before the loop The following program illustrates this characteristic of the while loop It displays a line of periods The number of periods displayed is equal to the value entered by the user The
506. t i char ch 2 int mairi u_type u 1000 u_type u2 H Y cout lt lt u as integer cout lt lt u i lt lt n cout lt lt u as chars u showchars cout lt lt u2 as integer cout lt lt uZ i lt lt n cout lt lt w2 as chars uz showchars return OQ The output is shown here u as integer 1000 u as chars u2 as integer 22872 u2 as chars X Y 24 Union data members share the same memory ch 1 y The data in a u_type object can be viewed as a short integer or as two characters C A Beginner s Guide by Herbert Schildt As the output shows using the u_type union it is possible to view the same data two different ways Like the structure the C union is derived from its C forerunner However in C unions can include only data members functions and constructors are not allowed In C the union has the expanded capabilities of the class But just because C gives unions greater power and flexibility does not mean that you have to use it Often unions contain only data However in cases where you can encapsulate a union along with the routines that manipulate it you will be adding considerable structure to your program by doing so There are several restrictions that must be observed when you use C unions Most of these have to do with features of C that will be discussed later in this book but they are mentioned here for completeness F
507. t main Test obl ob32 obl setab 10 20 ob2 setab 0 0 cout lt lt obl before assignment n obl1 showab cout lt lt ob2 before assignment n ob2 showab cout lt lt n ob2 obl assign obl to ob2 lt Assign one object to another 3 C A Beginner s Guide by Herbert Schildt cout lt lt obl after assignment n ob1 showab cout lt lt ob2 after assignment n ob2 showab cout lt lt n obl setab 1 1 change obl cout lt lt obl after changing obl n obl showab cout lt lt ob2 after changing obl n ob2 showab return OQ This program displays the following output obl before assignment ais 10 b is 20 ob2 before assignment ais 0 b is 0 obl after assignment ais 10 b is 20 eb2 after assignment ais 10 b is 20 obl after changing obl ais l b is 1 ob2 after changing obl a is 10 b is 20 As the program shows the assignment of one object to another creates two objects that contain the same values The two objects are otherwise still completely separate Thus a subsequent modification of one object s data has no effect on that of the other However you will need to watch for side effects which may still occur For example if an object A contains a pointer to some other object B then when a copy of A is made the copy will also contain a field that points to B Thus changing B will affect both obj
508. tance The following program creates a base class called TwoDShape that stores the width and height of a two dimensional object and a derived class called Triangle Pay close attention to the way that Triangle is declared A simple class hierarchy include lt iostream gt include lt cstring gt using namespace std A class for two dimensional objects class TwoDShape public double width double height void showDim cout lt lt Width and height are lt lt width lt lt and lt lt height lt lt n Triangle is derived from TwoDShape class Triangle public TwoDShape Triangle inherits TwoDShape public Notice the syntax char style 20 double area return width height 2 Triangle can refer to the members of TwoDShape as if they were part of Triangle void showStyle cout lt lt Triangle is lt lt style lt lt yn 2 C A Beginner s Guide by Herbert Schildt int main Triangle t1 Triangle t2 tl width 4 0 _ All members of Triangle are ti height 4 0 available to Triangle objects even those inherited from TwoDShape strcpy t1 style 1sosceles t2 width 8 0 t2 height 12 0 strepy t2 style right cout lt lt Info for t1 n tl showstyle t1l showDim cout lt lt Area is lt lt tl area lt lt n cout lt lt n cout lt lt Inf
509. tangle int width int height public Rectangle Add a parameterless constructor width height QO cout lt lt Constructing lt lt width lt lt by lt lt height lt lt rectangle n Rectangle int w int h width w height h cout lt lt Constructing lt lt width lt lt by lt lt height lt lt rectangle n Rectangle cout lt lt Destructing lt lt width lt lt by lt lt height lt lt rectangle n 33 C A Beginner s Guide by Herbert Schildt void set int w int h Add the set function width w height h int area return width height i int mair Rectangle p try f p new Rectangle 3 catch bad alloc xa cout lt lt Allocation Failure n return 1 cout lt lt n PplLO set 3 4 p 1 set 10 8 pl2 set 5 6 i for int i 0 i lt 3 i cout lt lt Area is lt lt p i area cout lt lt n delete p This calls the destructor for each object in the array return OQ The output from this program is shown here Constructing 0 by 0 rectangle Constructing 0 by 0 rectangle Constructing 0 by 0 rectangle Area is 12 Area is 80 Area is 30 Destructing 5 by 6 rectangle Destructing 10 by 8 rectangle Destructing 3 by 4 rectangle 34 lt lt endl C A Beginner s Guide by Herbert Schildt Because the pointe
510. tart the series over again from 0 Demonstrate your functions in a program Hint You will need to use a global variable 8 Write a program that requires a password that is specified on the command line Your program doesn t have to actually do anything except report whether the password was entered correctly or incorrectly 39 C A Beginner s Guide by Herbert Schildt 9 A prototype prevents a function from being called with the improper number of arguments True or false 10 Write a recursive function that prints the numbers 1 through 10 Demonstrate its use in a program 40 C A Beginner s Guide by Herbert Schildt Module6 A Closer Look at Functions Table of Contents CRITICAL SKILL 6 1 Know the two approaches to argument passing CRITICAL SKILL 6 2 How C Passes Arguments CRITICAL SKILL 6 3 Using a Pointer to Create a Call by Reference CRITICAL SKILL 6 4 Reference Parameters CRITICAL SKILL 6 5 Returning References CRITICAL SKILL 6 6 Independent References CRITICAL SKILL 6 7 Function Overloading CRITICAL SKILL 6 8 Default Function Arguments CRITICAL SKILL 6 9 Function Overloading and Ambiguity This module continues our examination of the function It discusses three of C s most important function related topics references function overloading and default arguments These features vastly expand the capabilities of a function A reference is an implicit pointer Function overloading is the quality
511. te which is an enumeration defined by ios that includes these members Name Meaning los goodbit No error bits set ios eofbit 1 when end of file is encountered 0 otherwise ios failbit 1 when a possibly nonfatal I O error has occurred 0 otherwise ios badbit 1 when a fatal I O error has occurred 0 otherwise There are two ways in which you can obtain I O status information First you can call the rdstate function It has this prototype iostate rdstate It returns the current status of the error flags As you can probably guess from looking at the preceding list of flags rdstate returns goodbit when no error has occurred Otherwise an error flag is turned on The other way you can determine if an error has occurred is by using one or more of these ios member functions bool bad bool eof bool fail bool good The eof function was discussed earlier The bad function returns true if badbit is set The fail function returns true if failbit is set The good function returns true if there are no errors Otherwise they return false Once an error has occurred it may need to be cleared before your program continues To do this use the ios member function clear whose prototype is shown here void clear iostate flags ios goodbit If flags is goodbit as it is by default all error flags are cleared Otherwise set flags to the settings you desire Before mo
512. te that some compilers may handle this differently 7 A break causes termination of its immediately enclosing loop or switch statement 5 C A Beginner s Guide by Herbert Schildt 8 After break executes after while is displayed 9 0 1 2 3 4 5 6 7 8 9 10 Use a for loop to generate the progression 124 8 16 aed include lt iostream gt using namespace std int main for int i 1 1 lt 100 i 1 cout lt lt 1 lt lt cout lt lt n return 0 11 Change case 6 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std int main char ch int changes 0 cout lt lt Enter period to stop n do cin gt gt ch 1f ch gt a amp amp ch lt z ch char 32 changes cout lt lt ch else if ch gt A amp amp ch lt Z ch char 32 changes t cout lt lt ch while ch cout lt lt nCase changes lt lt changes lt lt n return 0 12 C s unconditional jump statement is the goto Module 4 Arrays Strings and Pointers 1 short int hightemps 31 2 zero 3 Find duplicates 7 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std int main int nume 1 1 2 3 4 2 5 4 7 7 for int 1 0 i lt 10 i for int j itl j lt 10 j i1f nums i nums j cout lt
513. ted For the sake of simplicity this example creates a non circular queue but with a little thought and effort you can easily transform it into a circular queue Step by Step 1 Create a file called Queue cpp 2 Although there are other ways to support a queue the method we will use is based upon an array That is an array will provide the storage for the items put into the queue This array will be accessed through two indices The put index determines where the next element of data will be stored The get index indicates at what location the next element of data will be obtained Keep in mind that the get operation is consumptive and it is not possible to retrieve the same element twice Although the queue that we will be creating stores characters the same logic can be used to store any type of object Begin creating the Queue class with these lines const int maxOsize 100 class Queue char q maxQsize this array holds the queue int size Maximum number of elements the queue can store int putloc getloc the put and get indices 27 C A Beginner s Guide by Herbert Schildt The const variable maxQsize defines the size of the largest queue that can be created The actual size of the queue is stored in the size field 3 The constructor for the Queue class creates a queue of a given size Here is the Queue constructor public Construct a queue of a specific length Queue int len Queue must be less than m
514. teger is specified then the C compiler will generate code that assumes that the high order bit of an integer is to be used as a sign flag If the sign flag is O then the number is positive if it is 1 then the number is negative Negative numbers are almost always represented using A C A Beginner s Guide by Herbert Schildt the two s complement approach In this method all bits in the number except the sign flag are reversed and then 1 is added to this number Finally the sign flag is set to 1 Signed integers are important for a great many algorithms but they have only half the absolute magnitude of their unsigned relatives For example assuming a 16 bit integer here is 32 767 Ohta et LA ate LIE For a signed value if the high order bit were set to 1 the number would then be interpreted as 1 assuming the two s complement format However if you declared this to be an unsigned int then when the high order bit was set to 1 the number would become 65 535 To understand the difference between the way that signed and unsigned integers are interpreted by C try this short program Hinclude lt iostream gt This program shows the difference between signed and unsigned integers using namespace std int main short int i a signed short integer short unsigned int 3 an unsigned short integer j 60000 e 40 000 is within the range of an unsigned Short int but is typically outside the
515. tement Next main calls myfunc Notice how this is achieved the function s name is followed by parentheses In this case the function call is a statement and therefore must end with a semicolon Next myfunc executes its cout statement and then returns to main when the closing is encountered In main execution resumes at the line of code immediately following the call to myfunc Finally main executes its second cout statement and then terminates The output is shown here In main Inside myfunc Back in main The way myfunc is called and the way that it returns represent a specific instance of a process that applies to all functions In general to call a function specify its name followed by parentheses When a function is called execution jumps to the function Execution continues inside the function until its closing curly brace is encountered When the function ends program execution returns to the caller at the statement immediately following the function call Notice this statement in the preceding program void myfunc myfunc s prototype As the comment states this is the prototype for myfunc Although we will discuss prototypes in detail later a few words are necessary now A function prototype declares the function prior to its definition The prototype allows the compiler to know the function s return type as well as the number and type of any parameters that the function may have The c
516. tement executes box is automatically called so that its return value can be obtained This value is then output There is no reason to first assign it to some variable In general a non void function can be used in any type of expression When the expression is evaluated the function is automatically called so that its return value can be obtained For example the following program sums the volume of three boxes and then displays the average volume Use box in an expression include lt iostream gt using namespace std use double data double box double length double width double height int main double sum sum b box 10 1 11 2 3 3 box 5 5 6 6 7 7 box 4 0 5 0 8 0 cout lt lt The sum of the volumes is lt lt sum lt lt n F cout lt lt The average volume is lt lt sum 3 0 lt lt n return 0 This version of box uses double data double box double length double width double height return length width height The output of this program is shown here The sum of the volumes is 812 806 The average volume is 270 935 10 C A Beginner s Guide by Herbert Schildt Progress Check 1 Show the two forms of the return statement 2 Cana void function return a value 3 Cana function call be part of an expression Scope Rules Up to this point we have been using variables without formally discussing where they can be declared how long the
517. test throw test This exception is caught by int main the catch statement in main cout lt lt start n try start a try block cout lt lt Inside try block n Xtest 0 Because Xtest is called from Xtest 1 within a try block its code is Xtest 2 also monitored for errors catch int 1 eatch an error cout lt lt Caught an exception value is cout lt lt i lt lt n cout lt lt end return 0 This program produces the following output start Inside try block Inside Xtest test is 0 Inside Xtest test is 1 Caught an exception value is 1 end As the output confirms the exception thrown in Xtest was caught by the exception handler in main A try block can be localized to a function When this is the case each time the function is entered the exception handling relative to that function is reset Examine this sample program 5 C A Beginner s Guide by Herbert Schildt A try block can be localized to a function include lt iostream gt using namespace std A try catch is reset each time a function is enter void Xhandler int test bry e This try bleck is local to Xhandler if test throw test catch int i cout lt lt Caught One Ex lt lt i lt lt n int main cout lt lt start n Ahnandler 1 Ahnandler 2 f A try block can be localized to a function includ
518. that will be substituted for the identifier each time it is encountered in the source file The identifier is called a macro name and the replacement process is called macro substitution The general form of the directive is define macro name character sequence Notice that there is no semicolon in this statement There can be any number of spaces between the identifier and the start of the character sequence but once the sequence begins it is terminated only by a newline For example if you wanted to use the word UP for the value 1 and the word DOWN for the value O you would declare these two defines define UP 1 define DOWN O These statements will cause the compiler to substitute a 1 or aO each time the name UP or DOWN is encountered in your source file For example the following will print 102 on the screen 1 C A Beginner s Guide by Herbert Schildt It is important to understand that the macro substitution is simply the replacing of an identifier with its associated string Therefore if you want to define a standard message you might write something like this define GETFILE Enter File Name cout lt lt GETFILE C will substitute the string Enter File Name when the macro name GETFILE is encountered To the compiler the cout statement will actually appear to be cout lt lt Enter File Name No text substitutions will occur if the macro name occurs within a quoted string For examp
519. the class Specifically member variables also called instance variables are the data defined by the class Member functions are the code that operates on that data Function is C s term for a subroutine Polymorphism Polymorphism from Greek meaning many forms is the quality that allows one interface to access a general class of actions A simple example of polymorphism is found in the steering wheel of an automobile The steering wheel the interface is the same no matter what type of actual steering mechanism is used That is the steering wheel works the same whether your car has manual steering power steering or rack and pinion steering Thus turning the steering wheel left causes the car to go left no matter what type of steering is used The benefit of the uniform interface is of course that once you know how to operate the steering wheel you can drive any type of car The same principle can also apply to programming For example consider a stack which is a first in last out list You might have a program that requires three different types of stacks One stack is used for integer values one for floating point values and one for characters In this case the algorithm that implements each stack is the same even though the data being stored differs In a non object oriented language you would be required to create three different sets of stack routines with each set using different names However because of polymor
520. the general form of an object that can then be used with any type of data You are saved from the tedium of creating separate implementations for each data type for which you want the algorithm to work The compiler automatically creates the specific versions of the class for you CRITICAL SKILL 12 4 Dynamic Allocation There are two primary ways in which a C program can store information in the main memory of the computer The first is through the use of variables The storage provided by variables is fixed at compile 26 C A Beginner s Guide by Herbert Schildt time and cannot be altered during the execution of a program The second way information can be stored is through the use of C s dynamic allocation system In this method storage for data is allocated as needed from the free memory area that lies between your program and its permanent storage area and the stack This region is called the heap Figure 12 1 shows conceptually how a C program appears in memory Dynamically allocated storage is determined at runtime Thus dynamic allocation makes it possible for your program to create variables that it needs during its execution It can create as many or as few variables as required depending upon the situation Dynamic allocation is often used to support such data structures as linked lists binary trees and sparse arrays Of course you are free to use dynamic allocation wherever you determine it to be of value Dynamic allo
521. the length in feet double m holds the conversion to meters int counter counter 0 Line counter is initially set to zero For f 1 0 lt 100 0 m 3 28 convert to meters cout lt lt lt lt Feet is lt lt m lt lt meters n counter lt Increment the line counter with each loop iteration every l th line print a blank line if counter 10 O _ counter is 10 cout lt lt n output a blank line output a blank line counter 0 reset the line counter return 3 Notice how counter is used to output a blank line after each ten lines It is initially set to zero outside the for loop Inside the loop it is incremented after each conversion When counter equals 10 a blank line is output counter is reset to zero and the process repeats 4 Compile and run the program Here is a portion of the output that you will see Notice that results that don t produce an even result include a fractional component 1 feet is 0 304878 meters 2 feet is 0 609756 meters 3 feet is 0 914634 meters 4 feet is 1 21951 meters 5 feet is 1 52439 meters 6 feet is 1 82927 meters 7 feet is 2 13415 meters 34 C A Beginner s Guide by Herbert Schildt 8 feet is 2 43902 meters 9 feet is 2 7439 meters 10 ated TZ LS 14 15 16 17 Lg L93 20 al 22 23 24 25 26 21 28 29 30 34 j2 23 34 So 36 37 38 39 40 feet feet feet fe
522. the program For example the value 101 is an integer literal Literals are also commonly referred to as constants For the most part literals and their usage are so intuitive that they have been used in one form or another by all the preceding sample programs Now the time has come to explain them formally C literals can be of any of the basic data types The way each literal is represented depends upon its type As explained earlier character literals are enclosed between single quotes For example a and are both character literals Integer literals are specified as numbers without fractional components For example 10 and 100 are integer constants Floating point literals require the use of the decimal point followed by the number s fractional component For example 11 123 is a floating point constant C also allows you to use scientific notation for floating point numbers All literal values have a data type but this fact raises a question As you know there are several different types of integers such as int short int and unsigned long int There are also three different floating point types float double and long double The question is How does the compiler determine the type of a literal For example is 123 23 a float or a double The answer to this question has two parts First the C compiler automatically makes certain assumptions about the type of a literal and second you can explicitly specify the ty
523. the program is shown here object is triangle Area is 48 object is rectangle Area is 100 object is rectangle 36 C A Beginner s Guide by Herbert Schildt Area is 40 object is triangle Area is 24 5 object 1S generic Error area must be overridden Area is 0 Let s examine this program closely First area is declared as virtual in TwoDShape class and is overridden by Triangle and Rectangle Inside TwoDShape area is given a placeholder implementation that simply informs the user that this function must be overridden by a derived class Each override of area supplies an implementation that is suitable for the type of object encapsulated by the derived class Thus if you were to implement an ellipse class for example then area would need to compute the area of an ellipse There is one other important feature in the preceding program Notice in main that shapes is declared as an array of pointers to TwoDShape objects However the elements of this array are assigned pointers to Triangle Rectangle and TwoDShape objects This is valid because a base class pointer can point to a derived class object The program then cycles through the array displaying information about each object Although quite simple this illustrates the power of both inheritance and virtual functions The type of object pointed to by a base class pointer is determined at runtime and acted on accordingly If an object is derived from TwoDShape then its
524. the set If it is not then ch is added and len is updated In either case newset is returned Thus the Original set is untouched by this operation 7 Overload so that it removes an element from the set as shown here Remove an element from the set Set Set operator char ch Set newset int 1 find ch 1 will be 1 if element not found copy and compress the remaining elements for int j 0 j lt len J 1f j i newset newset members j return newset This function starts by creating a new null set Then find is called to determine the index of ch within the original set Recall that find returns 1 if ch is not a member Next the elements of the original set are added to the new set except for the element whose index matches that returned by find Thus the resulting set contains all of the elements of the original set except for ch If ch was not part of the original set to begin with then the two sets are equivalent 8 Overload the and again as shown here These versions implement set union and set difference Set union Set Set operator Set ob2 Set newset this copy the first set Add unique elements from second set for int i 0 i lt ob2 len i newset newset ob2 members i return newset return updated set Set difference Set Set operator Set ob2 Set newset this copy the first set Subtract elements from second set for i
525. the stack and execution resumes at the point just after the recursive call inside the function Recursive functions could be said to telescope out and back Keep in mind that most recursive routines do not significantly reduce code size Also the recursive versions of most routines may execute a bit more slowly than their iterative equivalents due to the added overhead of the additional function calls Too many recursive calls to a function may cause a stack overrun Because storage for function parameters and local variables is on the stack and each new call creates a new copy of these variables it is possible that the stack will be exhausted If this occurs other data may be destroyed as well However you probably will not have to worry about any of this unless a recursive function runs wild The main advantage of recursive functions is that they can be used to create versions of several algorithms that are clearer and simpler than those produced with their iterative relatives For example the Quicksort sorting algorithm is quite difficult to implement in an iterative way Also some problems especially those related to artificial intelligence seem to lend themselves to recursive solutions When writing a recursive function you must include a conditional statement such as an if somewhere to force the function to return without execution of the recursive call If you don t provide the conditional statement then once you call the funct
526. the value entered by the user which must be an integer in this case is put into the variable that is on the right side of the gt gt in this case length Thus after the cin statement executes length will contain the rectangle s length If the user enters a nonnumeric response length will be zero The statements that prompt and read the width work in the same way Some Output Options So far we have been using the simplest types of cout statements However cout allows much more sophisticated output statements Here are two useful techniques First you can output more than one 20 C A Beginner s Guide by Herbert Schildt piece of information using a single cout statement For example in the area program these two lines are used to display the area cout lt lt The area is cout lt lt length width These two statements can be more conveniently coded as shown here cout lt lt The area is lt lt length width This approach uses two output operators within the same cout statement Specifically it outputs the string The area is followed by the area In general you can chain together as many output operations as you like within one output statement Just use a separate lt lt for each item Second up to this point there has been no occasion to advance output to the next line that is to execute a Carriage return linefeed sequence However the need for this will arise very soon In C the
527. the values of the enumeration The variable list is optional because variables may be declared later using the enumeration type name The following fragment defines an enumeration called transport and two variables of type transport called t1 and t2 enum transport car truck airplane train boat t1 t2 Once you have defined an enumeration you can declare additional variables of its type using its name For example this statement declares one variable called how of enumeration transport transport how The statement can also be written like this enum transport how However the use of enum here is redundant In C which also supports enumerations this second form was required so you may see it used in some programs Assuming the preceding declarations the following gives how the value airplane 12 C A Beginner s Guide by Herbert Schildt how airplane The key point to understand about an enumeration is that each of the symbols stands for an integer value As such they can be used in any integer expression Unless initialized otherwise the value of the first enumeration symbol is O the value of the second symbol is 1 and so forth Therefore cout lt lt car lt lt lt lt train displays 0 3 Although enumerated constants are automatically converted to integers integers are not automatically converted into enumerated constants For example the following statement is incorrect how 1 Error
528. tively and refer to macro names The general form of ifdef is ifdef macro name statement sequence endif If macro name has been previously defined in a define statement the statement sequence between the ifdef and endif will be compiled The general form of ifndef is ifndef macro name statement sequence endif If macro name is currently undefined by a define statement then the block of code is compiled Both the ifdef and ifndef can use an else or elif statement Also you can nest ifdefs and ifndefs in the same way as ifs undef The undef directive is used to remove a previously defined definition of a macro name The general form is undef macro name Consider this example define TIMEOUT 100 define WAIT 0 II undef TIMEOUT undef WAIT Here both TIMEOUT and WAIT are defined until the undef statements are encountered The principal use of undef is to allow macro names to be localized to only those sections of code that need them g C A Beginner s Guide by Herbert Schildt Using defined In addition to ifdef there is a second way to determine if a macro name is defined You can use the if directive in conjunction with the defined compile time operator For example to determine if the macro MYFILE is defined you can use either of these two preprocessing commands if defined MYFILE or ifdef MYFILE You can also precede defined with the to reverse the condition For example the
529. to 4 294 967 295 short int 32 748 to 32 767 32 68 to 32 767 unsigned short int signed short int 0 fo 65 535 long int Same as int signed long int Same as signed int unsigned long int Same as unsigned int float 1 8E 38 to 3 4E 38 double 2 2E 308 to BE 208 long double 2 2E 308 to 1 8E 308 bool N A True or false wehar_t l 0 to 65 535 Table 2 2 Typical Bit Widths and Ranges for the C Data Types in a 32 Bit Environment Integers As you learned in Module 1 variables of type int hold integer quantities that do not require fractional components Variables of this type are often used for controlling loops and conditional statements and for counting Because they don t have fractional components operations on int quantities are much faster than they are on floating point types Because integers are so important to programming C defines several varieties As shown in Table 2 1 there are short regular and long integers Furthermore there are signed and unsigned versions of each A signed integer can hold both positive and negative values By default integers are signed Thus the use of signed on integers is redundant but allowed because the default declaration assumes a signed value An unsigned integer can hold only positive values To create an unsigned integer use the unsigned modifier The difference between signed and unsigned integers is in the way the high order bit of the integer is interpreted If a signed in
530. tput is right justified When the internal flag is set a numeric value is padded to fill a field by inserting spaces between any sign or base character If none of these flags is set output is right justified by default By default numeric values are output in decimal However it is possible to change the number base Setting the oct flag causes output to be displayed in octal Setting the hex flag causes output to be displayed in hexadecimal To return output to decimal set the dec flag Setting showbase causes the base of numeric values to be shown For example if the conversion base is hexadecimal the value 1F will be displayed as Ox1F By default when scientific notation is displayed the e is in lowercase Also when a hexadecimal value is displayed the x is in lowercase When uppercase is set these characters are displayed in uppercase Setting showpos causes a leading plus sign to be displayed before positive values Setting showpoint causes a decimal point and trailing zeros to be displayed for all floating point output whether needed or not By setting the scientific flag floating point numeric values are displayed using scientific notation When fixed is set floating point values are displayed using normal notation When neither flag is set the compiler chooses an appropriate method When unitbuf is set the buffer is flushed after each insertion operation When boolalpha is set Booleans can be input or output using the
531. trlen char str int i for i 0 str i i find the end of the string return 1 5 No a local variable s value is lost when its function returns Or more generally its value is lost when its block is exited 6 The main advantages to global variables are that they are available to all other functions in the program and that they stay in existence during the entire lifetime of the program Their main disadvantages are that they take up memory the entire time the program is executing using a global where a local variable will do makes a function less general and using a large number of global variables can lead to unanticipated side effects 11 C A Beginner s Guide by Herbert Schildt include lt iostream gt using namespace std int seriesnum 0 int byThrees void reset int main for int i 0 i lt 10 i cout lt lt byThrees lt lt cout lt lt n reset for int 1 0 1 lt 10 i cout lt lt byThrees lt lt cout lt lt n return 0 int byThrees int t t seriesnum seriesnum 3 return CT void reset seriesnum 0 12 C A Beginner s Guide by Herbert Schildt include lt iostream gt include lt cstring gt using namespace std int main int argc char argv if arge 2 cout lt lt Password required n return 0 if stremp mypassword argv 1 cout lt lt Access permitted n el
532. tructors destructors do not have return types Here is a simple example that uses a constructor and a destructor A simple constructor and destructor include lt iostream gt using namespace std class MyClass public int x 15 C A Beginner s Guide by Herbert Schildt Declare constructor and destructor MyClass constructor Declare constructor ar MyClass destructor _ destructor for MyClas Implement MyClass constructor MyClass MyClass x 10 Implement MyClass destructor MyClass MyClass cout lt lt Destructing n int main MyClass obl MyClass oba2 cout lt lt obl x lt lt lt lt ob2 x lt lt n return OQ The output from the program is shown here 10 10 Destructing Destructing In this example the constructor for MyClass is Implement MyClass constructor MyClass MyClass x 10 Notice that the constructor is specified under public This is because the constructor will be called from code defined outside of its class This constructor assigns the instance variable x of MyClass the value 10 This constructor is called when an object is created For example in the line MyClass ob1 the constructor MyClass is called on the ob1 object giving ob1 x the value 10 The same is true for ob2 After construction ob2 x also has the value 10 The destructor for MyClass is shown next
533. true when the end of the file has been reached otherwise it returns false peek and putback You can obtain the next character in the input stream without removing it from that stream by using peek It has this prototype int peek peek returns the next character in the stream or EOF if the end of the file is encountered The character is contained in the low order byte of the return value You can return the last character read from a stream to that stream by using putback Its prototype is shown here istream amp putback char c where c is the last character read flush When output is performed data is not immediately written to the physical device linked to the stream Instead information is stored in an internal buffer until the buffer is full Only then are the contents of that buffer written to disk However you can force the information to be physically written to disk before the buffer is full by calling flush Its prototype is shown here ostream amp flush Calls to flush might be warranted when a program is going to be used in adverse environments in situations where power outages occur frequently for example NOTE Closing a file or terminating a program also flushes all buffers ccmaes A File Comparison Utility This project develops a simple yet useful file comparison utility It works by opening both files to be compared and then reading and comparing each corresponding s
534. uages at the time such as Pascal C was the first to successfully combine power elegance and expressiveness Its terse yet easy to use syntax coupled with its philosophy that the programmer not the language was in charge quickly won many converts It can be a bit hard to understand from today s perspective but C was a breath of fresh air that programmers had long awaited As a result C became the most widely used structured programming language of the 1980s The Need for C Given the preceding discussion you might be wondering why C was invented Since C was a successful computer programming language why was there a need for something else The answer is complexity Throughout the history of programming the increasing complexity of programs has driven the need for better ways to manage that complexity C is a response to that need To better understand the correlation between increasing program complexity and computer language development consider the following Approaches to programming have changed dramatically since the invention of the computer For example when computers were first invented programming was done by using the computer s front panel to toggle in the binary machine instructions As long as programs were just a few hundred instructions long this approach worked As programs grew assembly language was invented so that programmers could deal with larger increasingly complex programs by using symbolic representati
535. uctor for Vehicle Vehicle int p int int m passengers p fuelcap f mpg m Compute and return the range int range return mpg fuelcap Define functions inline and access Accessor functions private variables through accessor int get_passengers return passengers functions lt h f int get_fuelcap return fuelcap int get_mpg return mpg int main Pass values to Vehicle constructor Vehicle minivan 7 16 21 Vehicle sportscar 2 14 12 int rangel range2 Compute the ranges assuming a full tank of gas rangel minivan range range2 sportscar range cout lt lt Minivan can carry lt lt minivan get_passengers lt lt with a range of lt lt rangel lt lt n Because the member variables of Vehicle are now private the accessor function get_passengers must be used inside main to obtain the number of passengers that a vehicle can hold Progress Check 1 What does inline do 2 Can an inline function be declared inside a class declaration 26 C A Beginner s Guide by Herbert Schildt 3 What is an accessor function ees Creating a Queue Class As you may know a data structure is a means of organizing data The simplest data structure is the array which is a linear list that supports random access to its elements Arrays are often used as the underpinning for more sophisticated data structures su
536. ue of an overloaded assignment operator is the object on the left after the assignment has been made This is in keeping with the traditional action of the operator For example to allow statements like A c c 31 C A Beginner s Guide by Herbert Schildt it is necessary for operator to return the object pointed to by this which will be the object that occurs on the left side of the assignment statement This allows a chain of assignments to be made The assignment operation is one of the most important uses of the this pointer In the preceding program it was not actually necessary to overload the because the default assignment operator provided by C is adequate for the ThreeD class As explained earlier in this module the default assignment operation is a bitwise copy The was overloaded simply to show the proper procedure In general you need to overload the only when the default bitwise copy cannot be used Because the default operator is sufficient for ThreeD subsequent examples in this module will not overload it Order Matters When overloading binary operators remember that in many cases the order of the operands does make a difference For example although A B is commutative A B is not That is A B is not the same as B A Therefore when implementing overloaded versions of the noncommutative operators you must remember which operand is on the left and which is on the right For exampl
537. uence n cout lt lt break n cout lt lt n cout lt lt n break case 3 cout lt lt The for n n cout lt lt for init condition increment cout lt lt statement n break case 4 cout lt lt The while n n cout lt lt while condition statement n break case 5 cout lt lt The do while n n cout lt lt do n cout lt lt statement n cout lt lt while condition n break case 6 cout lt lt The break n n cout lt lt break n break case 7J cout lt lt The continue n n cout lt lt continue n break case 8 cout lt lt The goto n n cout lt lt goto label n break cout lt lt n 5 Create the showmenu function Show the help menu void Help showmenu 11 C A Beginner s Guide by Herbert Schildt cout cout cout cout cout cout cout cout cout cout 6 Create the isvalid function shown here lt lt Help on n i lt lt lt lt lt lt lt lt 7 lt lt lt lt 1 9 lt lt Choose one o amp WwW bo 1f n switch n forn while n do while n breakin continue n goto n q to quit Return true if a selection is valid bool Help isvalid char ch 1f ch return false else return true ral ei E l ch gt 8 amp amp ch I q 7 Rew
538. uide by Herbert Schildt class cl int 1 private by default public inline functions int get_i return i void put_i int j Short functions like those illustrated in this example are usually defined inside the class declaration In class inline functions are quite common when working with classes because frequently a public function provides access to a private variable Such functions are called accessor functions Part of successful object oriented programming is controlling access to data through member functions Because most C programmers define accessor functions and other short member functions inside their classes this convention will be followed by the rest of the C examples in this book It is an approach that you should use too Here is the Vehicle class recoded so that its constructor destructor and range function are defined inside the class Also the passengers fuelcap and mpg fields have been made private and accessor functions have been added to get their values 25 C A Beginner s Guide by Herbert Schildt Defines constructor destructor and range function in line tinclude lt iostream gt using namespace std Declare the Vehicle class Make these class Vehicle variables private These are now private int passengers number of passengers int fuelcap fuel capacity in gallons int mpg uel consumption in miles per gallon public This is a constr
539. umed that chars are signed entities The type char can hold values other than just the ASCII character set It can also be used as a small integer with the range typically from 128 through 127 and can be substituted for an int when the situation does not require larger numbers For example the following program uses a char variable to control the loop that prints the alphabet on the screen if This program displays the alphabet tinclude lt iostream gt using namespace std int main i Use a char variable char letter to control a for loop for letter A letter lt S letter cout lt lt letter return U The for loop works because the character A is represented inside the computer by the value 65 and the values for the letters A to Z are in sequential ascending order Thus letter is initially set to A Each time through the loop letter is incremented Thus after the first iteration letter is equal to B The type wchar_t holds characters that are part of large character sets As you may know many human languages such as Chinese define a large number of characters more than will fit within the 8 bits provided by the char type The wchar_t type was added to C to accommodate this situation While we 6 C A Beginner s Guide by Herbert Schildt won t be making use of wchar_t in this book it is something that you will want to look into if you are tailoring programs for the internatio
540. unctions just like any other values Of course it is necessary to declare the parameters as pointer types To see how passing a pointer allows you to manually create a call by reference consider a function called swap that exchanges the values of the two variables pointed to by its arguments Here is one way to implement it Exchange the values of the variables pointed to by x and y void swap int x int y int temp temp m save the value at addressx Exchange the values ke y put y into x of the variables y temp put x into y pointed to by x and y The swap function declares two pointer parameters x and y It uses these parameters to exchange the values of the variables pointed to by the arguments passed to the function Remember x and y refer to the variables pointed to by x and y Thus the statement Ky y x y puts the value of the object pointed to by y into the object pointed to by x Consequently when the function terminates the contents of the variables used to call the function will be swapped Since swap expects to receive two pointers you must remember to call swap with the addresses of the variables you want to exchange The correct method is shown in this program Demonstrate the pointer version of swap include lt iostream gt using namespace std Declare swap using pointers void swap int x int y 3 C A Beginner s Guide by Herbert Schi
541. ur program defines a class by the same name a conflict will arise The creation of the namespace keyword was a response to these problems Because it localizes the visibility of names declared within it a namespace allows the same name to be used in different contexts without conflicts arising Perhaps the most noticeable beneficiary of namespace is the C standard library Prior to namespace the entire C library was defined within the global namespace which was of course the only namespace Since the addition of namespace the C library is now defined within its own namespace called std which reduces the chance of name collisions You can also create your own namespaces within your program to localize the visibility of any names that you think may cause conflicts This is especially important if you are creating class or function libraries Namespace Fundamentals The namespace keyword allows you to partition the global namespace by creating a declarative region In essence a namespace defines a scope The general form of namespace is shown here namespace name declarations 35 C A Beginner s Guide by Herbert Schildt Anything defined within a namespace statement is within the scope of that namespace Here is an example of a namespace It localizes the names used to implement a simple countdown counter class In the namespace are defined the counter class which implements the counter and the variables upperbound and low
542. ure members are public by default int main Test s s put_i 10 cout lt lt s get_i return OQ This simple program defines a structure type called Test in which get_i and put_i are public and i is private Notice the use of the keyword private to specify the private elements of the structure The following program shows an equivalent program that uses a class instead of a struct include lt iostream gt using namespace std class Test int 1 private by default public int get_i return i void put_i int j i j i int main Test s S put_i 10 cout lt lt s get_i return O Ask the Expert Q Since struct and class are so similar why does C have both 22 C A Beginner s Guide by Herbert Schildt A On the surface there is seeming redundancy in the fact that both structures and classes have virtually identical capabilities Many newcomers to C wonder why this apparent duplication exists In fact it is not uncommon to hear the suggestion that either the keyword class or struct is unnecessary The answer to this line of reasoning is rooted in the desire to keep C compatible with C As C is currently defined a standard C structure is also a completely valid C structure In C which has no concept of public or private structure members all structure members are public by default This is why members of C structures are public rather than private by
543. urn value is assigned to x You can also use a Call to a function in an expression For example x MyFune Z 10 In this case the return value from MyFunc is added to 10 and the result is assigned to x In general whenever a function s name is encountered in a statement it is automatically called so that its return value can be obtained To review an argument is a value passed into a function A return value is data that is passed back to the calling code Here is a short program that demonstrates how to call a function It uses one of C s built in functions called abs to display the absolute value of a number The abs function takes one argument converts it into its absolute value and returns the result 36 C A Beginner s Guide by Herbert Schildt ii Use the abs function inelude lt iostream gt include lt cstdlib gt using namespace std int maint int result result abs 10 4 The calls the abs function and assigns its return value to result cout lt lt result return Here the value 10 is passed as an argument to abs The abs function receives the argument with which it is called and returns its absolute value which is 10 in this case This value is assigned to result Thus the program displays 10 on the screen Notice one other thing about the preceding program it includes the header cstdlib This is the header required by abs Wheneve
544. urpose of C is to allow this barrier to be broken and to help the programmer comprehend and manage larger more complex programs C Is Born C was invented by Bjarne Stroustrup in 1979 at Bell Laboratories in Murray Hill New Jersey He initially called the new language C with Classes However in 1983 the name was changed to C Stroustrup built C on the foundation of C including all of C s features attributes and benefits He also adhered to C s underlying philosophy that the programmer not the language is in charge At this point it is critical to understand that Stroustrup did not create an entirely new programming language Instead he enhanced an already highly successful language Most of the features that Stroustrup added to C were designed to support object oriented programming In essence C is the object oriented version of C By building upon the foundation of C Stroustrup provided a smooth migration path to OOP Instead of having to learn an entirely new language a C programmer needed to learn only a few new features before reaping the benefits of the object oriented methodology When creating C Stroustrup knew that it was important to maintain the original spirit of C including its efficiency flexibility and philosophy while at the same time adding support for object oriented programming Happily his goal was accomplished C still provides the programmer with the freedom and control of C coupled
545. urse the ANSI ISO C standard stipulates that the variable is known only within the statement in which it is declared Most programmers do not declare variables inside any control statement other than the for In fact the declaration of variables within the other statements is controversial with some programmers suggesting that to do so is bad practice CRITICAL SKILL 3 6 Using break to Exit a Loop It is possible to force an immediate exit from a loop bypassing the loop s conditional test by using the break statement When the break statement is encountered inside a loop the loop is immediately terminated and program control resumes at the next statement following the loop Here is a simple example include lt iostream gt using namespace std 27 C A Beginner s Guide by Herbert Schildt int main int t Loops from 0 to 9 not to 100 for t 0 t100 t if t 10 break lt Break out of the for when t equals 10 cout lt lt t lt lt return OQ The output from the program is shown here 0123456789 As the output illustrates this program prints only the numbers O through 9 on the screen before ending It will not go to 100 because the break statement will cause it to terminate early When loops are nested that is when one loop encloses another a break will cause an exit from only the innermost loop Here is an example include lt iostream gt using namesp
546. used to describe polymorphism Part of the key to successfully applying polymorphism is understanding that the base and derived classes form a hierarchy which moves from greater to lesser generalization base to derived When designed correctly the base class provides all of the elements that a derived class can use directly It also defines those functions that the derived class must implement on its own This allows the derived class the flexibility to define its own methods and yet still enforces a consistent interface That is since the form of the interface is defined by the base class any derived class will share that common interface Thus the use of virtual functions makes it possible for the base class to define the generic interface that will be used by all derived classes At this point you might be asking yourself why a consistent interface with multiple implementations is important The answer again goes back to the central driving force behind object oriented programming It helps the programmer handle increasingly complex programs For example if you develop your program correctly then you know that all objects you derive from a base class are accessed in the same general way even if the specific actions vary from one derived class to the next This means that you need to deal with only one interface rather than several Also your derived class is free to use any or all of the functionality provided by the base class You need
547. uses the do while loop shown here do cout lt lt Help on n cout lt lt 1 if n cout lt lt 2 switch n cout lt lt 3 for n cout lt lt 4 while n cout lt lt 5 do while n cout lt lt Choose one cin gt gt choice while choice lt 1 choice gt 5 After making this change the program will loop displaying the menu until the user enters a response that is between 1 and 5 You can see how useful the do while loop is in this context 3 Expand the switch statement to include the for while and do while loops as shown here switch choice case l1 cout lt lt The if n n cout lt lt if condition statement n cout lt lt else statement n break case 2 cout lt lt The switch n n cout lt lt switch expression n cout lt lt case constant n cout lt lt statement sequencen 24 C A Beginner s Guide by Herbert Schildt cout lt lt cout lt lt cout lt lt break a cout lt lt case cout lt lt cout lt lt break case d4 cout lt lt cout lt lt break case 5 cout lt lt cout lt lt cout lt lt cout lt lt break break n j ii ae n pAn The for n n for init condition statement n increment The while n n while condition statement n The do while n n do n statement n while condition
548. using namespace std int main char choice for do 31 C A Beginner s Guide by Herbert Schildt cout cout cout cout cout cout cout Cout cout cout lt lt lt lt lt lt lt _ lt lt lt a Help on n 1 B Choose one LE n switch n forn while n do while n break n continue n goto n r q to quit cin gt gt choice while i f choice cout lt lt choice lt 1 choice gt 8 amp amp choice q break m n n switch choice 32 Case 1 1 E cout lt lt cour lt lt Cour lt lt break Case 2 Cout cout Case Case Case cout cout cout cout cout lt lt lt lt lt lt _ lt lt lt _ lt lt _ lt break cout cout cout 14 e lt lt break cout cout 4 lt _ lt break cout cout cout rR s lt lt lt The 1f n n 1 condition statement n else statement n The switch n n switch expression n case constant n statement sequencen break n Af NDI hn The for n n for init statement n condition increment The while n n while condition statement n The do while n n do n statement n C A Beginner s Guide by Herbert Schildt q cout lt lt while co
549. ut lt lt n s3 sl s2 cout lt lt s3 after s3 sl s2 s3 showset s3 83 sI cout lt lt s3 after s3 sl s3 showset 53 sl n m C A Beginner s Guide by Herbert Schildt cout lt lt n cout lt lt s2 after s2 s2 sa s2 s2 s2 clear s2 s2 showset cout lt lt n s2 s2 C add ABC in reverse order s2 82 B s2 82 A cout lt lt s2 after adding C B A sz2 showset return Q The output from this program is shown here sl after adding ABC ABC Testing for membership using isMember Bis a member of sl T is not a member of s1 sl after sl sl B AC sl after sl sl A C sl after al sl C sl after adding ABC ABC s2 after adding A XW AXW s3 after s3 sl s2 f ABC XW s3 after s3 sl AW s2 after s s2 s2 s2 after adding C BA CBA Module 9 Mastery Check 1 What is a copy constructor and when is it called Show the general form of a copy constructor 2 Explain what happens when an object is returned by a function Specifically when is its destructor called 54 C A Beginner s Guide by Herbert Schildt 3 Given this class class T int i jJ public int sum return i j show how to rewrite sum so that it uses this 4 What is a structure What is a union 5 Inside a member function to what does this r
550. ut lt lt nClearing showpos for cout n cout unsetf ios showpos f cout vebece Clear the showpos flag 1 f f amp ios showpos cout lt lt showpos is set for cout n else cout lt lt showpos is cleared for cout n return OQ The program produces this output showpos is cleared for cout Setting showpos for cout showpos is set for cout Clearing showpos for cout showpos is cleared for cout In the program notice that the type fmtflags is preceded by ios when f is declared This is necessary since fmtflags is a type defined by ios In general whenever you use the name of a type or enumerated constant that is defined by a class you must qualify it with the name of the class Setting the Field Width Precision and Fill Character 13 C A Beginner s Guide by Herbert Schildt In addition to the formatting flags there are three member functions defined by ios that set these additional format values the field width the precision and the fill character The functions that set these values are width precision and fill respectively Each is examined in turn By default when a value is output it occupies only as much space as the number of characters it takes to display it However you can specify a minimum field width by using the width function Its prototype is shown here streamsize width streamsize w Here w becomes the field width and the previous field width is return
551. ut lt lt i lt lt while i gt lowerbound cout lt lt endl ob2 reset 100 lowerbound 90 do i ob2 run cout lt lt i lt lt while i gt Lowerbound return O The program illustrates one other important point using one namespace does not override another When you bring a namespace into view it simply adds its names to whatever other namespaces are currently in effect Thus by the end of the program both std and CounterNameSpace have been added to the global namespace Unnamed Namespaces There is a special type of namespace called an unnamed namespace that allows you to create identifiers that are unique within a file It has this general form 40 C A Beginner s Guide by Herbert Schildt namespace declarations Unnamed namespaces allow you to establish unique identifiers that are known only within the scope of a single file That is within the file that contains the unnamed namespace the members of that namespace may be used directly without qualification But outside the file the identifiers are unknown As mentioned earlier in this book one way to restrict the scope of a global name to the file in which it is declared is to declare it as static While the use of static global declarations is still allowed in C a better way to accomplish this is to use an unnamed namespace The std Namespace Standard C defines its entire library in its own namespace called std This
552. ut fully specifying the data upon which it will operate Once a template class has been defined specific instances of the template class can be created As it relates to the I O library Standard C creates two specific versions of these template classes one for 8 bit characters and another for wide characters These specific versions act like any other classes and no familiarity with templates is required to fully utilize the C I O system The C I O system is built upon two related but different template class hierarchies The first is derived from the low level I O class called basic_streambuf This class supplies the basic low level input and output operations and provides the underlying support for the entire C I O system Unless you are doing advanced I O programming you will not need to use basic_streambuf directly The class hierarchy that you will most commonly be working with is derived from basic_ios This is a high level I O class that provides formatting error checking and status information related to stream I O A base class for basic_ios is called ios_base which defines several traits used by basic_ios basic_ios is used as a base for several derived classes including basic_istream basic_ostream and basic_iostream These classes are used to create streams capable of input output and input output respectively 3 C A Beginner s Guide by Herbert Schildt As explained the I O library creates two specific versions
553. value of num bits determines how many bit places the bits are shifted Each left shift causes all bits within the specified variable to be shifted left one position and a zero bit to be brought in on the right Each right shift shifts all bits to the right one position and brings in a zero on the left However if the variable is a signed integer containing a negative value then each right shift brings in a 1 on the left which preserves the sign bit Remember a shift is not a rotation That is the bits shifted off of one end do not come back around to the other 22 C A Beginner s Guide by Herbert Schildt The shift operators work only with integral types such as int char long int or short int They cannot be applied to floating point values for example Bit shift operations can be very useful for decoding input from external devices such as D A converters and for reading status information The bitwise shift operators can also be used to perform very fast multiplication and division of integers A shift left will effectively multiply a number by 2 and a shift right will divide it by 2 The following program illustrates the effects of the shift operators Example of bitshifting include lt iostream gt using namespace std void show_binary unsigned int u int main int i l t f f shift left for t 0 t lt 8 t show_binary i i i lt lt 1 leftshift i one position cout lt lt n shi
554. ver some special rules apply Remember also that you may need to surround some parts of a pointer expression with parentheses in order to ensure that the outcome is what you desire Pointer Arithmetic There are only four arithmetic operators that can be used on pointers and To understand what occurs in pointer arithmetic let p1 be an int pointer with a current value of 2 000 that is it contains the address 2 000 Assuming 32 bit integers after the expression p1 the contents of p1 will be 2 004 not 2 001 The reason for this is that each time p1 is incremented it will point to the next int The same is true of decrements For example again assuming that p1 has the value 2000 the expression 27 C A Beginner s Guide by Herbert Schildt p1 causes p1 to have the value 1996 Generalizing from the preceding example the following rules apply to pointer arithmetic Each time that a pointer is incremented it will point to the memory location of the next element of its base type Each time it is decremented it will point to the location of the previous element of its base type In the case of character pointers an increment or decrement will appear as normal arithmetic because characters are one byte long However every other type of pointer will increase or decrease by the length of its base type You are not limited to only increment and decrement operations You can also add or subtract integers t
555. ving on you might want to experiment with using these status reporting functions to add extended error checking to the preceding file examples Module 11 Mastery Check 1 What are the four predefined streams called 38 C A Beginner s Guide by Herbert Schildt 2 Does C define both 8 bit and wide character streams 3 Show the general form for overloading an inserter 4 What does ios scientific do 5 What does width do 6 An I O manipulator is used within an I O expression True or false 7 Show how to open a file for reading text input 8 Show how to open a file for writing text output 9 What does ios binary do 10 When the end of the file is reached the stream variable will evaluate as false True or false 11 Assuming a file is associated with an input stream called strm show how to read to the end of the file 12 Write a program that copies a file Allow the user to specify the name of the input and output file on the command line Make sure that your program can copy both text and binary files 13 Write a program that merges two text files Have the user specify the names of the two files on the command line in the order they should appear in the output file Also have the user specify the name of the output file Thus if the program is called merge then the following command line will merge the files MyFile1 txt and MyFile2 txt into Target txt merge MyFile1 txt MyFile2 txt Target txt 14 Show ho
556. w the seekg statement will seek to the 300th byte in a stream called MyStrm 39 C A Beginner s Guide by Herbert Schildt Module12 Exceptions Templates and Other Advanced Topics Table of Contents CRITICAL SKILL 12 1 Exception Handling CRITICAL SKILL 12 2 Generic Functions CRITICAL SKILL 12 3 Generic Classes CRITICAL SKILL 12 4 Dynamic Allocation CRITICAL SKILL 12 5 Namespaces CRITICAL SKILL 12 6 static Class Members CRITICAL SKILL 12 7 Runtime Type Identification RTTI CRITICAL SKILL 12 8 The Casting Operators You have come a long way since the start of this book In this the final module you will examine several important advanced C topics including exception handling templates dynamic allocation and namespaces Runtime type ID and the casting operators are also covered Keep in mind that C is a large sophisticated professional programming language and it is not possible to cover every advanced feature specialized technique or programming nuance in this beginner s guide When you finish this module however you will have mastered the core elements of the language and will be able to begin writing real world programs 1 C A Beginner s Guide by Herbert Schildt CRITICAL SKILL 12 1 Exception Handling An exception is an error that occurs at runtime Using C s exception handling subsystem you can ina structured and controlled manner handle runtime errors When exception handling is
557. wing output Stare Caught One Caught One Caught One end Xhandler throws three types of exceptions int char and double All are caught using the catch statement One very good use for catch is as the last catch of a cluster of catches In this capacity it provides a useful default or catch all statement Using catch as a default is a good way to catch all exceptions that you don t want to handle explicitly Also by catching all exceptions you prevent an unhandled exception from causing an abnormal program termination Specifying Exceptions Thrown by a Function You can specify the type of exceptions that a function can throw outside of itself In fact you can also prevent a function from throwing any exceptions whatsoever To accomplish these restrictions you must add a throw clause to a function definition The general form of this clause is 10 C A Beginner s Guide by Herbert Schildt ret type func name arg list throw type list Here only those data types contained in the comma separated type list can be thrown by the function Throwing any other type of expression will cause abnormal program termination If you don t want a function to be able to throw any exceptions then use an empty list NOTE at the time of this writing Visual C does not actually prevent a function from throwing an exception type that is not specified in the throw clause This is nonstandard behavior
558. with the name of the namespace followed by the scope resolution operator Here is a program that demonstrates the use of the CounterNameSpace Demonstrate a namespace tinclude lt iostream gt using namespace std namespace CounterNamespace int upperbound int lowerbound class counter int count public counter int n 1f n lt upperbound count else count upperbound void reset int n ifin lt upperbound count int run 1 count gt lLowerbound else return lowerbound int main CounterNamespace upperbound CounterNamespace lowerbound return count 100 Oo Explicitly refer to members of l CounterNameSpace Note the use of the scope resolution operator CounterNamespace counter ob1 10 int i do i obl run cout lt lt 1 lt lt while i gt CounterNameSpace lowerbound cout lt lt endl CounterNamespace counter ob2 20 37 C A Beginner s Guide by Herbert Schildt do 1 ob2 run cout lt lt i lt lt while i gt CounterNameSpace lowerbound cout lt lt endl ob2 reset 100 CounterNamesSpace lowerbound 90 do 1 ob2 run cout lt lt i lt lt while i gt CounterNameSpace lowerbound return 0 Notice that the declaration of a counter object and the references to upperbound and lowerbound are qualified by CounterNameSpace However once an object of type count
559. with the power of objects Although C was initially designed to aid in the management of very large programs it is in no way limited to this use In fact the object oriented attributes of C can be effectively applied to virtually any programming task It is not uncommon to see C used for projects such as editors databases personal file systems networking utilities and communication programs Because C shares C s efficiency much high performance systems software is constructed using C Also C is frequently the language of choice for Windows programming The Evolution of C Since C was first invented it has undergone three major revisions with each revision adding to and altering the language The first revision was in 1985 and the second in 1990 The third occurred during the C standardization process Several years ago work began on a standard for C Toward that end a joint ANSI American National Standards Institute and ISO International Standards Organization standardization committee was formed The first draft of the proposed standard was created on January 25 1994 In that draft the ANSI ISO C committee of which was a member kept the features first defined by Stroustrup and added some new ones But in general this initial draft reflected the state of C at the time Soon after the completion of the first draft of the C standard an event occurred that caused the standard to be greatly expanded the
560. wledge to make full use of this in depth C guide Module 12 Mastery Check 1 Explain how try catch and throw work together to support exception handling 2 How must the catch list be organized when catching exceptions of both base and derived classes 3 Show how to specify that a MyExcpt exception can be thrown out of a function called func that returns void 4 Define an exception for the generic Queue class shown in Project 12 1 Have Queue throw this exception when an overflow or underflow occurs Demonstrate its use 5 What is a generic function and what keyword is used to create one 6 Create generic versions of the quicksort and qs functions shown in Project 5 1 Demonstrate their use 7 Using the Sample class shown here create a queue of three Sample objects using the generic Queue shown in Project 12 1 class Sample int id public Sample id 0 Sample int x id x void show cout lt lt id lt lt endl 8 Rework your answer to question 7 so that the Sample objects stored in the queue are dynamically allocated 9 Show how to declare a namespace called RobotMotion 10 What namespace contains the C standard library 11 Can a static member function access the non static data of a class 12 What operator obtains the type of an object at runtime 52 C A Beginner s Guide by Herbert Schildt 13 14 15 16 To determine the validity of a polymorphic cast
561. wo operations are fundamentally different however and applying function overloading in this manner defeats its original purpose In fact programming in this manner is considered to be extremely bad style In practice you should overload only closely related operations Automatic Type Conversions and Overloading As you will recall from Module 2 C provides certain automatic type conversions These conversions also apply to parameters of overloaded functions For example consider the following Automatic type conversions can affect overloaded function resolution 17 C A Beginner s Guide by Herbert Schildt 7 include lt iostream gt using namespace std void f int x void f double x int main int i 10 double d 10 1 short s 99 float r 11 5F f i calls f int f d calls double f s calls f 1int type conversion Automatic type f r calls double type conversion conversions occur here return 0 void f int x cout lt lt Inside int lt lt x lt lt yn void f double x cout lt lt Inside f double lt lt x lt lt n The output from the program is shown here f int 10 Inside f double 10 1 Inside E int 99 f double 11 5 Inside Inside In this example only two versions of f are defined one that has an int parameter and one that has a double parameter However it is possible to pass f a
562. x yields a pointer to the first element of the array Q Are pointers and arrays interchangeable A As the preceding few pages have shown pointers and arrays are strongly related and are interchangeable in many cases For example a pointer that points to the beginning of an array can access that array using either pointer arithmetic or array style indexing However pointers and arrays are not completely interchangeable For example consider this fragment int nums 10 int i for i 0 i lt 10 i nums i this is OK nums ERROR cannot modify nums Here nums is an array of integers As the comments describe while it is perfectly acceptable to apply the operator to nums which is a pointer operation it is illegal to modify nums value The reason for this is that nums is a constant that points to the beginning of an array Thus you cannot increment it More generally while an array name without an index does generate a pointer to the beginning of an array it cannot be changed Although an array name generates a pointer constant it can still take part in pointer style expressions as long as it is not modified For example the following is a valid statement that assigns nums 3 the value 100 nums 3 100 This is OK because nums is not changed String Constants 33 C A Beginner s Guide by Herbert Schildt You might be wondering how string constants like the one in the fragment shown here are h
563. y opl y op2 temp zZz opl z op return temp This allows int ThreeD ThreeD operator int opl ThreeD op2 ThreeD temp temp op2Z x opl temp y op2 y opl temp Z opZ2 z opl return temp Show X Y Z coordinates void ThreeD show cout lt lt x lt lt cout lt lt y lt lt cout lt lt z lt lt n int main ThreeD a l 2 3 b cout lt lt Original value of a a show cout lt lt n b a 10 object integer cout lt lt Value of b after b a 10 b show 41 C A Beginner s Guide by Herbert Schildt cout lt lt n Here the built in type occurs on the left side of an addition b 10 a integer object cout lt lt Value of b after b 10 a e b show return 0 The output is shown here Original value of a 1 2 3 Value of b after b a 10 11 12 13 Value of b after b 10 a 11 12 13 Because the operator function is overloaded twice it can accommodate the two ways in which an integer and an object of type ThreeD can occur in the addition operation Using a Friend to Overload a Unary Operator You can also overload a unary operator by using a friend function However if you are overloading the or you must pass the operand to the function as a reference parameter Since a reference parameter is an implicit pointer to the argument changes to the parameter will af
564. y it occurs after the default private members are declared and before the public members Thus the most common full form of a class declaration is class class name private members by default protected protected members public public members Of course the protected category is optional In addition to specifying protected status for members of a class the keyword protected can also act as an access specifier when a base class is inherited When a base class is inherited as protected all public and protected members of the base class become protected members of the derived class For example in the preceding example if D inherited B as shown here class D protected B then all non private members of B would become protected members of D Progress Check 1 When a base class is inherited as private public members of the base class become private members of the derived class True or false Can a private member of a base class be made public through inheritance 3 To make a member accessible within a hierarchy but private otherwise what access specifier do you use Ask the Expert Q Can you review public protected and private A When a class member is declared as public it can be accessed by any other part of a program When a member is declared as private it can be accessed only by members of its class Further derived classes do not have access to private base class members When a member is decl
565. y reference not call by value Thus it can exchange the two arguments it is called with void swap int amp x int amp y int temp f use references to exchange the values of the arguments temp X x y Now the exchange takes place y temp automatically through the references 6 C A Beginner s Guide by Herbert Schildt passes the address of val not its value to f There is no need to precede val with the amp operator Doing so would be an error Since f receives the address of val in the form of a reference it can modify the value of val To illustrate reference parameters in actual use and to fully demonstrate their benefits the swap function is rewritten using references in the following program Look carefully at how swap is declared and called Use reference parameters to create the swap function include lt iostream gt using namespace std Declare swap using reference parameters void swap int amp x int amp y int main int i J i 10 j 20 cout lt lt Initial values of i and j Here swap is defined as using call by reference not call by value Thus it can exchange the two arguments it is called with void swap int amp x int amp y int temp use references to exchange the values of the arguments temp x x y Now the exchange takes place y temp automatically through the references The output is the
566. y remain in existence and what parts of a program have access to them These attributes are determined by the scope rules defined by C In general the scope rules of a language govern the visibility and lifetime of an object Although C defines a finely grained system of scopes there are two basic ones local and global In both of these scopes you can declare variables In this section you will see how variables declared ina local scope differ from variables declared in the global scope and how each relates to the function CRITICAL SKILL 5 6 Local Scope A local scope is created by a block Recall that a block begins with an opening curly brace and ends with a closing curly brace Thus each time you start a new block you are creating a new scope A variable can be declared within any block A variable that is declared inside a block is called a local variable A local variable can be used only by statements located within the block in which it is declared Stated another way local variables are not known outside their own code blocks Thus statements defined outside a block cannot access an object defined within it In essence when you declare a local variable you are localizing that variable and protecting it from unauthorized access and or modification Indeed the scope rules provide the foundation for encapsulation One of the most important things to understand about local variables is that they exist only while the block
567. y used parts Specifically it shows how to overload the lt lt and gt gt operators so that you can input or output objects of classes that you design It describes how to format output and how to use I O manipulators The module ends by discussing file I O Old vs Modern C I O There are currently two versions of the C object oriented I O library in use the older one that is based upon the original specifications for C and the newer one defined by Standard C The old I O library is supported by the header file lt iostream h gt The new I O library is supported by the header 1 C A Beginner s Guide by Herbert Schildt lt iostream gt For the most part the two libraries appear the same to the programmer This is because the new I O library is in essence simply an updated and improved version of the old one In fact the vast majority of differences between the two occur beneath the surface in the way that the libraries are implemented not in how they are used From the programmer s perspective there are two main differences between the old and new C I O libraries First the new I O library contains a few additional features and defines some new data types Thus the new I O library is essentially a superset of the old one Nearly all programs originally written for the old library will compile without substantive changes when the new library is used Second the old style I O library was in the global namespace The n
568. you will find the name of the header that must be included in order to use that function Progress Check 1 What is a function prototype What is the purpose of a prototype 2 Aside from main must all functions be prototyped 31 C A Beginner s Guide by Herbert Schildt 3 When you use a standard library function why must you include its header CRITICAL SKILL 5 12 Recursion The last topic that we will examine in this module is recursion Sometimes called circular definition recursion is the process of defining something in terms of itself As it relates to programming recursion is the process of a function calling itself A function that calls itself is said to be recursive The classic example of recursion is the function factr which computes the factorial of an integer The factorial of a number N is the product of all the whole numbers between 1 and N For example 3 factorial is 1x2x3 or 6 Both factr and its iterative equivalent are shown here Demonstrate recursion include lt iostream gt 32 C A Beginner s Guide by Herbert Schildt using namespace std int factr int n int factfint n int main use recursive version cout lt lt 4 factorial is lt lt factr 4 cout lt lt n use iterative version cout lt lt 4 factorial is lt lt fact 4 cout lt lt n return 0 Recursive version int factr int n int answer 1f nm 1
569. zeof compile time operator which has these general forms sizeof type sizeof var name The first version returns the size of the specified data type and the second returns the size of the specified variable As you can see if you want to know the size of a data type such as int you must enclose the type name in parentheses If you want to know the size of a variable no parentheses are needed although you can use them if you desire To see how sizeof works try the following short program For many 32 bit environments it displays the values 1 4 4 and 8 33 C A Beginner s Guide by Herbert Schildt Demonstrate sizeof include lt iostream gt using namespace std int main char ch int i cout lt lt sizeof ch lt lt size of char cout lt lt sizeof i lt lt size of int cout lt lt sizeof float lt lt size of float cout lt lt sizeof double lt lt size of double return 0 You can apply sizeof to any data type For example when it is applied to an array it returns the number of bytes used by the array Consider this fragment Assuming 4 byte integers this fragment displays the value 16 that is 4 bytes times 4 elements As mentioned earlier sizeof is a compile time operator All information necessary for computing the size of a variable or data type is known during compilation The sizeof operator primarily helps you to generate portable cod

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