Wiley Professional C++
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1. Create and populate an employee EmployeeT anEmployee anEmployee anEmployee anEmployee anEmployee anEmployee Output the values of an employee ng ae Og ore MY Men middleInitial R llaisicitiastieieul Weep employeeNumber 42 salary 80000 11 Chapter 1 cout lt lt Employee lt lt anEmployee firstInitial lt lt anEmployee middleInitial lt lt anEmployee lastInitial lt lt endl cout lt lt Number lt lt anEmployee employeeNumber lt lt endl cout lt lt Salary lt lt anEmployee salary lt lt endl return 0 Conditionals Conditionals let you execute code based on whether or not something is true There are three main types of conditionals in C If Else Statements The most common conditional is the if statement which can be accompanied by else If the condition given inside the if statement is true the line or block of code is executed If not execution continues to the else case if present or to the code following the conditional The following pseudocode shows a cas cading if statement a fancy way of saying that the if statement has an else statement that in turn has another if statement and so on tac ab S 4 4 Do something else if i gt 2 Do something else else Do something else The expression between the parentheses of an if statement must be a Boolean value or evaluate to a Boolean value Conditional operato2. 10 Behind the scenes an enumerated type is just an integer value The real value of kPieceTypeKing is A Crash Course in C zero However by defining the possible values for variables of type PieceT your compiler can give you a warning or error if you attempt to perform arithmetic on PieceT variables or treat them as integers The following code which declares a PieceT variable then attempts to use it as an integer results in a warning on most compilers PieceT myPiece myPiece 0 Structs Structs let you encapsulate one or more existing types into a new type The classic example of a struct is a database record If you are building a personnel system to keep track of employee information you will need to store the first initial last initial middle initial employee number and salary for each employee A struct that contains all of this information is shown in the header file that follows employeestruct h typedef struct char firs einitialt char middleInitial char lastInitial int employeeNumber Ine salary EmployeeT A variable declared with type EmployeeT will have all of these fields built in The individual fields of a ww struct can be accessed by using the character The example that follows creates and then outputs the record for an employee structtest cpp include lt iostream gt include employeestruct h using namespace std int main int argc char argv
3. Unary operator to decrement a variable by 1 i i Shorthand syntax fori i j i j Shorthand syntax for i j i i j i 9 die Se PG i j S a ieee a a SS 5 2 SS O amp Takes the raw bits of one variable and performs a i j amp k amp bitwise and with the other variable j amp k Takes the raw bits of one variable and performs a Eseje k bitwise or with the other variable j k A Crash Course in C Operator Description Usage lt lt Takes the raw bits of a variable and shifts each i i lt lt 1 gt gt bit left lt lt or right gt gt the specified number of i i gt gt 4 lt lt places i lt lt 1 gt gt i gt gt 4 R Performs a bitwise exclusive or operation on E D MPS St the two arguments I asg The following program shows the most common variable types and operators in action If you re unsure about how variables and operators work try to figure out what the output of this program will be and then run it to confirm your answer typetest cpp include lt iostream gt using namespace std int main int argc char argv int someInteger 256 short someShort long someLong float someFloat double someDouble someInteger someInteger 2 someShort short someInteger someLong someShort 10000 someFloat someLong 0 785 someDouble double someFloat 100000 cout lt lt someDou
4. A Crash Course in C The goal of this chapter is to cover briefly the most important parts of C so that you have a base of knowledge before embarking on the rest of the book This chapter is not a comprehensive lesson in the C programming language The very basic points like what a program is and the differ ence between and are not covered The very esoteric points remember what a union is how about the volatile keyword are also omitted Certain parts of the C language that are less rele vant in C are also left out as are parts of C that get in depth coverage in later chapters This chapter aims to cover the parts of C that programmers encounter on a daily basis If you ve been away from C for a while and you ve forgotten the syntax for a for loop you ll find that in this chapter If you re fairly new to C and you don t understand what a reference variable is you ll learn that here as well If you already have significant experience with C skim this chapter to make sure that there aren t any fundamental parts of the language on which you need to brush up If you re new to C take the time to read this chapter carefully and make sure that you understand the examples If you need additional introductory information consult the titles listed in Appendix B The Basics of C The C language is often viewed as a better C or a superset of C Many of the annoyances or rough edges of the C langua
5. Q m m m Q Q The ability to view all former employees The design for this program divides the code into three parts The Employee class encapsulates the information describing a single employee The Database class manages all the employees of the com pany A separate UserInter face file provides the interactivity of the program The Employee Class The Employee class maintains all the information about an employee Its methods provide a way to query and change that information Employees also know how to display themselves on the console Methods also exist to adjust the employee s salary and employment status 29 Chapter 1 Employee h 30 The Employee h file declares the behavior of the Employee class The sections of this file are described individually in the material that follows Employee h include lt iostream gt namespace Records The first few lines of the file include a comment indicating the name of the file and the inclusion of the stream functionality This code also declares that the subsequent code contained within the curly braces will live in the Records namespace Records is the namespace that is used throughout this program for application specific code const int kDefaultStartingSalary 30000 This constant representing the default starting salary for new employees lives in the Records names pace Other code that lives in Records can access this constant simply as kD
6. The ternary operator is represented by a and a The following code will output yes if the variable i is greater than 2 and no otherwise std cout lt lt i1 gt 2 yes no The advantage of the ternary operator is that it can occur within almost any context In the preceding example the ternary operator is used within code that performs output A convenient way to remember how the syntax is used is to treat the question mark as though the statement that comes before it really is a question For example Is i greater than 2 If so the result is yes if not the result is no Unlike an if statement or a switch statement the ternary operator doesn t execute code based on the result Instead it is used within code as shown in the preceding example In this way it really is an oper ator like and as opposed to a true conditional such as if and switch Conditional Operators You have already seen a conditional operator without a formal definition The gt operator compares two values The result is true if the value on the left is greater than the value on the right All conditional operators follow this pattern they all result ina true or false The table below shows other common conditional operators Operator Description Usage lt Determines if the left hand side if i lt 0 lt is less than less than or equal to std cout lt lt i is negative g
7. gt gt employeeNumber cout lt lt How much of a raise cin gt gt raiseAmount A Crash Course in C EIA YL Employee amp emp inDB getEmployee employeeNumber emp promote raiseAmount catch std exception ex cerr lt lt Unable to promote employee lt lt endl doFire and doPromote both ask the database for an employee by their employee number and then use the public methods of the Employee object to make changes Evaluating the Program The preceding program covers a number of topics from the very simple to the more obscure There are a number of ways that you could extend this program For example the user interface does not expose all of the functionality of the Database or Employee classes You could modify the UI to include those fea tures You could also change the Database class to remove fired employees from the mEmployees array potentially saving space If there are parts of this program that don t make sense consult the preceding sections to review those topics If something is still unclear the best way to learn is to play with the code and try things out For example if you re not sure how to use the ternary operator write a short main function that tries it out Summary Now that you know the fundamentals of C you are ready to become a professional C programmer The next five chapters will introduce you to several important design concepts By covering design
8. if it is Note that after their use the mNext Slot and mNextEmployeeNumber data members are incremented so that the next employee will get a new slot and number Employee amp Database getEmployee int inEmployeeNumber icone siaye ao Oe ak lt WWedeSilojeg a4s if mEmployees i getEmployeeNumber inEmployeeNumber return mEmployees i cerr lt lt No employee with employee number lt lt inEmployeeNumber lt lt endl throw exception Employee amp Database getEmployee string inFirstName string inLastName for int i 0 i lt mNextSlot i if mEmployees i getFirstName inFirstName amp amp mEmployees i getLastName inLastName return mEmployees i cerr lt lt No match with name lt lt inFirstName lt lt lt lt inLastName lt lt endl throw exception Both versions of getEmployee work in similar ways The methods loop over all nonblank employees in the mEmployees array and check to see if each Employee is a match for the information passed to the method If no match is found an error is output and an exception is thrown 36 A Crash Course in C void Database displayAl11 ore tie 2 Of L a meelo e if mEmployees i display void Database displayCurrent ore ses L Of 2 miNescteSiloie a if if mEmployees i getIsHired mEmployees i display void Database displayFormer oie Ghar
9. like this are covered in Chapter 12 as an Object Oriented Language If you are a C programmer you may have viewed the features covered so far in this chapter as convenient additions to the C language As the name C implies in many ways the language is just a better C There is one major point that this view overlooks Unlike C C is an object oriented language Object oriented programming OOP is a very different arguably more natural way to write code If you are used to procedural languages such as C or Pascal don t worry Chapter 3 covers all the back ground information you need to know to shift your mindset to the object oriented paradigm If you already know the theory of OOP the rest of this section will get you up to speed or refresh your mem ory on basic C object syntax Declaring a Class 26 A class defines the characteristics of an object It is somewhat analogous to a struct except a class defines behaviors in addition to properties In C classes are usually declared in a header file and fully defined in a corresponding source file A basic class definition for an airline ticket class is shown below The class can calculate the price of the ticket based on the number of miles in the flight and whether or not the customer is a member of the Elite Super Rewards Program The definition begins by declaring the class name Inside a set of curly braces the data members properties of the class and i
10. lt WO Oue ee eeg cout lt lt endl Colbie K lt Vesa gt ty cin gt gt selection return selection 39 Chapter 1 The displayMenu function simply outputs the menu and gets input from the user One important note is that this code assumes that the user will play nice and type a number when a number is requested When you read about I O in Chapter 14 you will learn how to protect against bad input void doHire Database amp inDB string firstName string lastName cout lt lt First name cin gt gt firstName cout lt lt Last name cin gt gt lastName try inDB addEmployee firstName lastName catch std exception ex cerr lt lt Unable to add new employee lt lt endl The doHire function simply gets the new employee s name from the user and tells the database to add the employee It handles errors somewhat gracefully by outputting a message and continuing 40 void doFire Database amp inDB int employeeNumber cout lt lt Employee number cin gt gt employeeNumber try Employee amp emp inDB getEmployee employeeNumber emp fire cout lt lt Employee lt lt employeeNumber lt lt has been terminated lt lt endl catch std exception ex cerr lt lt Unable to terminate employee lt lt endl void doPromote Database amp inDB int employeeNumber int raiseAmount cout lt lt Employee number cin
11. Most compilers offer a strict mode that will turn off these nonstandard extensions to the language To allocate an array dynamically you first need to declare a pointer int myVariableSizedArray The after the int type indicates that the variable you are declaring refers to some integer memory in the heap Think of the pointer as an arrow that points at the dynamically allocated heap memory It does not yet point to anything specific because you haven t assigned it to anything it is an uninitialized variable To initialize the pointer to new heap memory you use the new command myVariableSizedArray new int arraySize This allocates memory for enough integers to satisfy the arraySize variable Figure 1 3 shows what the stack and the heap both look like after this code is executed As you can see the pointer variable still resides on the stack but the array that was dynamically created lives on the heap Stack Heap myVariableSizedArray O myVariableSizedArray 1 myVariableSizedArray 2 myVariableSizedArray myVariableSizedArray 3 myVariableSizedArray 4 myVariableSizedArray 5 myVariableSizedArray 6 myVariableSizedArray 7 Figure 1 3 19 Chapter 1 Now that the memory has been allocated you can work with myVariableSizedArray as though it were a regular stack based array myVariableSizedArray 3 2 When your code is done with the array i
12. Records int displayMenu void doHire Database amp inDB void doFire Database amp inDB void doPromote Database amp inDB void doDemote Database amp inDB int main int argc char argv Database employeeDB bool done false while done int selection displayMenu switch selection 38 A Crash Course in C case 1 doHire employeeDB break case 2 doFire employeeDB break case 3 doPromote employeeDB break case 4 employeeDB displayAl1 break case 5 employeeDB displayCurrent break case 6 employeeDB displayFormer break case 0 done true break default cerr lt lt Unknown command lt lt endl return 0 The main function is a loop that displays the menu performs the selected action then does it all again For most actions separate functions are defined For simpler actions like displaying employees the actual code is put in the appropriate case int displayMenu int selection cout lt lt endl cout lt lt Employee Database lt lt endl cout eea uee endik cout lt lt 1 Hire a new employee lt lt endl cout lt lt 2 Fire an employee lt lt endl cout lt lt 3 Promote an employee lt lt endl cout lt lt 4 List all employees lt lt endl cout lt lt 5 List all current employees lt lt endl cout lt lt 6 List all previous employees lt lt endl Corie lt
13. able as the size it must be a constant value The code that follows shows the declaration of an array of 10 integers followed by a for loop that initializes each integer to zero int myArray 10 DESETO 0 for ink lt 0 myArray i 15 Chapter 1 The preceding example shows a one dimensional array which you can think of as a line of integers each with its own numbered compartment C allows multidimensional arrays You might think of a two dimensional array as a checkerboard where each location has a position along the x axis and a position along the y axis Three dimensional and higher arrays are harder to picture and are rarely used The code below shows the syntax for allocating a two dimensional array of characters for a Tic Tac Toe board and then putting an o in the center square char ticTacToeBoard 3 3 ticTacToeBoard 1 1 o Figure 1 1 shows a visual representation of this board with the position of each square ticTacToeBoard O O ticTacToeBoard O 1 ticTacToeBoard 0O 2 ticTacToeBoard 1 O ticTacToeBoard 1 1 ticTacToeBoard 1 2 ticTacToeBoard 2 O ticTacToeBoard 2 1 ticTacToeBoard 2 2 Figure 1 1 In C the first element of an array is always at position 0 not position 1 The last position of the array is always the size of the array minus 1 Functions 16 For programs of any significant size pla
14. an T Socketwrench Ticket setNumberOfMiles 700 int cost myTicket calculatePriceInDollars Gove ss Mimie piekert vaill Cose ST ss COSE lt lt Suci AirlineTicket myTicket2 Heap based AirlineTicket my my my my Ticket2 new AirlineTicket Allocate a new object Ticket2 gt setPassengerName Laudimore M Hallidue Ticket2 gt setNumberOfMiles 2000 Ticket2 gt setHasEliteSuperRewardsStatus true int cost2 myTicket2 gt calculatePriceInDollars cout lt lt This other ticket will cost lt lt cost2 lt lt endl del lete myTicket2 return 0 27 Chapter 1 28 The definitions of the AirlineTicket class methods are shown below AirlineTicket cpp include lt iostream gt include AirlineTicket h using namespace std AirlineTicket AirlineTicket Initialize data members fHasEliteSuperRewardsStatus false mPassengerName Unknown Passenger mNumberOfMiles 0 AirlineTicket AirlineTicket Nothing much to do in terms of cleanup int AirlineTicket calculatePriceInDollars if getHasEliteSuperRewardsStatus Elite Super Rewards customers fly for free return 0 The cost of the ticket is the number of miles times 0 1 Real airlines probably have a more complicated formula return static_cast lt int gt getNumberOfMiles 0 1 string AirlineTicket getPassengerName return mPassengerName v
15. at a high level without getting into too much actual code you will gain an appreciation for good program design without getting bogged down in the syntax When you start getting deeper into the C language later in the book refer back to this chapter to brush up on parts of the language that you may need to review Going back to some of the sample code in this chapter may be all you need to see to bring a forgotten concept back to the forefront of your mind 41
16. ble lt lt endl The C compiler has a recipe for the order in which expressions are evaluated If you have a compli cated line of code with many operators the order of execution may not be obvious For that reason it s probably better to break up a complicated statement into several smaller statements or explicitly group expressions using parentheses For example the following line of code is confusing unless you happen to know the C operator precedence table by heart int i 34 8 2 21 7 2 Adding parentheses makes it clear which operations are happening first int i 34 8 2 21 7 2 Chapter 1 Breaking up the statement into separate lines makes it even clearer Int I S gE 2 ine S20 fT j 2 E T O EE E 4 For those of you playing along at home all three approaches are equivalent and end up with i equal to 51 If you assumed that C evaluated expressions from left to right your answer would have been 1 In fact C evaluates and first in left to right order followed by addition and subtraction then bitwise operators Parenthesis let you explicitly tell the compiler that a certain operation should be eval uated separately Types In C you can use the basic types int bool etc to build more complex types of your own design Once you are an experienced C programmer you will rarely use the following techniques which are features brought in from C because classes are far
17. cing all the code inside of main is unmanageable To make programs easy to understand you need to break up or decompose code into concise functions In C you first declare a function to make it available for other code to use If the function is used inside a particular file of code you generally declare and define the function in the source file If the function is for use by other modules or files you generally put the declaration in a header file and the definition in a source file A Crash Course in C Function declarations are often called function prototypes or signatures to emphasize that they represent how the function can be accessed but not the code behind it A function declaration is shown below This example has a return type of void indicating that the func tion does not provide a result to the caller The caller must provide two arguments for the function to work with an integer and a character void myFunction int i char c Without an actual definition to match this function declaration the link stage of the compilation process will fail because code that makes use of the function myFunction will be calling nonexistent code The following definition simply prints the values of the two parameters void myFunction int i char c Siecle scols lt lt Tee well OE 1 as 7 lt lt a lt lt siecissEiniclils std cout lt lt the value of c is lt lt c lt lt std endl Els
18. compilers Chapter 1 will issue a warning if you assign a float to an int without an explicit cast If you are certain that the left hand side type is fully compatible with the right hand side type it s okay to cast implicitly Operators What good is a variable if you don t have a way to change it The table below shows the most common operators used in C and sample code that makes use of them Note that operators in C can be binary operate on two variables unary operate on a single variable or even ternary operate on three vari ables There is only one ternary operator in C and it is covered in the next section Conditionals Operator Description Usage Binary operator to assign the value on the right to int the variable on the left i 3 int j j i Unary operator to negate the true false non 0 0 bool b true status of a variable bool b2 b Binary operator for addition int a sa 2 int j i 5 int k i j Binary operators for subtraction multiplication int i 5 1 and division int j 5 2 Int k 3 6 4 Binary operator for remainder of a division int remainder 5 2 operation Also referred to as the mod operator Unary operator to increment a variable by 1 If the i operator occurs before the variable the result of i the expression is the unincremented value If the operator occurs after the variable the result of the expression is the new value
19. cords are kept in a fixed size array Because the database will also take care of automati cally assigning an employee number to a new employee a constant defines where the numbering begins class Database public Database Database Employee amp addEmployee std string inFirstName std string inLastName Employee amp getEmployee int inEmployeeNumber Employee amp getEmployee std string inFirstName std string inLastName The database provides an easy way to add a new employee by providing a first and last name For con venience this method will return a reference to the new employee External code can also get an 34 A Crash Course in C employee reference by calling the getEmployee method Two versions of this method are declared One allows retrieval by employee number The other requires a first and last name void displayAl1 void displayCurrent void displayFormer Because the database is the central repository for all employee records it has methods that will output all employees the employees who are currently hired and the employees who are no longer hired protected Employee mEmployees kMaxEmployees int mNextSlot int mNextEmployeeNumber Ie The mEmployees array is a fixed size array that contains the Employee objects When the database is created this array will be filled with nameless employees all with an employee number of 1 When the addEmployee met
20. d be able to handle it include lt iostream gt include lt stdexcept gt int main int argc char argv coya std cout lt lt divideNumbers 2 5 0 5 lt lt std endl std cout lt lt divideNumbers 2 3 0 lt lt std endl catch std exception exception std cout lt lt An exception was caught lt lt std endl The first call to divideNumbers executes successfully and the result is output to the user The second call throws an exception No value is returned and the only output is the error message that is printed when the exception is caught The output for the preceding block of code is 5 An exception was caught Exceptions can get tricky in C To use exceptions properly you need to understand what happens to the stack variables when an exception is thrown and you have to be careful to properly catch and han dle the necessary exceptions The preceding example used the built in std exception exception type but it is preferable to write your own exception types that are more specific to the error being thrown Unlike the Java language the C compiler doesn t force you to catch every exception that might occur A Crash Course in C If your code never catches any exceptions but an exception is thrown it will be caught by the program itself which will be terminated These trickier aspects of exceptions are covered in much more detail in Chapter 15 The Many Uses of const The keyword c
21. e Number lt lt getEmployeeNumber lt lt endl The display method uses the console output stream to display information about the current employee Because this code is part of the Employee class it could access data members such as mSalary directly instead of using the getSalary accessor However it is considered good style to make use of accessors when they exist even within the class Accessors and setters void Employee setFirstName string inFirstName mFirstName inFirstName string Employee getFirstName Ht return mFirstName void Employee setLastName string inLastName mLastName inLastName string Employee getLastName return mLastName A Crash Course in C void Employee setEmployeeNumber int inEmployeeNumber 3 EmployeeNumber inEmployeeNumber int Employee getEmployeeNumber return mEmployeeNumber void Employee setSalary int inSalary mSalary inSalary int Employee getSalary return mSalary bool Employee getIsHired return fHired A number of accessors and setters perform the simple task of getting and setting values Even though these methods seem trivial it s better to have trivial accessors and setters than to make your data mem bers public In the future you may want to perform bounds checking in the setSalary method for example EmployeeTest cpp As you write ind
22. e value of the parameter it will not compile In the following code a char is automatically cast toa const char in the call to mysteryFunction If the author of mysteryFunction attempts to change the values within the character array the code will not compile There are actually ways around this restriction but using them requires conscious effort C only protects against accidentally changing const variables consttest cpp void mysteryFunction const char myString int main int argc char argv char myString new char 2 moer tael Tarp mocca 9 O mysteryFunction myString return 0 25 Chapter 1 Const References C You will often find code that uses const reference parameters At first that seems like a contradiction Reference parameters allow you to change the value of a variable from within another context const seems to prevent such changes The main value in const reference parameters is efficiency When you pass a variable into a function an entire copy is made When you pass a reference you are really just passing a pointer to the original so the computer doesn t need to make the copy By passing a const reference you get the best of both worlds no copy is made but the original variable cannot be changed const references become more important when you are dealing with objects because they can be large and making copies of them can have unwanted side effects Subtle issues
23. e you can define the context in which names are defined To place code in a namespace simply enclose it within a namespace block namespaces h namespace mycode void foo A Crash Course in C The implementation of a method or function can also be handled in a namespace namespaces cpp include lt iostream gt include namespaces h namespace mycode void foo std cout lt lt foo called in the mycode namespace lt lt std endl By placing your version of foo in the namespace mycode it is isolated from the foo function provided by the third party library To call the namespace enabled version of foo prepend the namespace onto the function name as follows mycode foo Calls the foo function in the mycode namespace Any code that falls within a mycode namespace block can call other code within the same namespace without explicitly prepending the namespace This implicit namespace is useful in making the code more precise and readable You can also avoid prepending of namespaces with the using directive This directive tells the compiler that the subsequent code is making use of names in the specified namespace The namespace is thus implied for the code that follows usingnamespaces cpp include namespaces h using namespace mycode int main int argc char argv foo Implies mycode foo J A single source file can contain multiple using directi
24. efaultStartingSalary Elsewhere it must be referenced as Records kDefaultStartingSalary class Employee public Employee void promote int inRaiseAmount 1000 void demote int inDemeritAmount 1000 void hire Hires or rehires the employee void fire Dismisses the employee void display Outputs employee info to the console Accessors and setters void setFirstName std string inFirstName std string getFirstName void setLastName std string inLastName std string getLastName void setEmployeeNumber int inEmployeeNumber suave getEmployeeNumber void setSalary int inNewSalary int getSalary bool getIsHired The Employee class is declared along with its public methods The promote and demote methods both have integer parameters that are specified with a default value In this way other code can omit the integer parameters and the default will automatically be used A Crash Course in C A number of accessors provide mechanisms to change the information about an employee or query the current information about an employee private std string mFirstName std string mLastName int mEmployeeNumber int mSalary bool fHired We Finally the data members are declared as private so that other parts of the code cannot modify them directly The accessors provide the only public way of modifying or querying these values Employee cpp The implementa
25. elpful If you are a C programmer with little C experience you should read this section carefully Pointers and Dynamic Memory Dynamic memory allows you to build programs with data that is not of fixed size at compile time Most nontrivial programs make use of dynamic memory in some form The Stack and the Heap Memory in your C application is divided into two parts the stack and the heap One way to visual ize the stack is as a deck of cards The current top card represents the current scope of the program usu ally the function that is currently being executed All variables declared inside the current function will take up memory in the top stack frame the top card of the deck If the current function which we ll call 00 calls another function bar a new card is put on the deck so that bar has its own stack frame to work with Any parameters passed from foo to bar are copied from the foo stack frame into the bar stack frame The mechanics of parameter passing and stack frames are covered in Chapter 13 Figure 1 2 shows what the stack might look like during the execution of a hypothetical function foo that has declared two integer values int i 7 intj 11 foo main Figure 1 2 Stack frames are nice because they provide an isolated memory workspace for each function If a vari able is declared inside the foo stack frame calling the bar function won t c
26. et you write code that scribbles on random memory addresses or tries to divide by zero computers don t deal well with infinity One of the language features that attempts to add a degree of safety back to the language is exceptions 23 Chapter 1 24 An exception is an unexpected situation For example if you are writing a function that retrieves a Web page several things could go wrong The Internet host that contains the page might be down the page might come back blank or the connection could be lost In many programming languages you would handle this situation by returning a special value from the function such as the NULL pointer Exceptions provide a much better mechanism for dealing with problems Exceptions come with some new terminology When a piece of code detects an exceptional situation it throws an exception Another piece of code catches the exception and takes appropriate action The fol lowing example shows a function divideNumbers that throws an exception if the caller passes in a denominator of zero include lt stdexcept gt double divideNumbers double inNumerator double inDenominator if inDenominator 0 throw std exception return inNumerator inDenominator When the throw line is executed the function will immediately end without returning a value If the caller surrounds the function call with a try catch block as shown in the following code it will receive the exception an
27. ewhere in the program you can make calls to myFunction and pass in constants or variables for the two parameters Some sample function calls are shown here myFunction 8 a myFunction someInt b myFunction 5 someChar In C unlike C a function that takes no parameters just has an empty parameter list It is not necessary to use void to indicate that no parameters are taken However you should still use void to indicate when no value is returned C functions can also return a value to the caller The following function declaration and definition is for a function that adds two numbers and returns the result int addNumbers int numberl int number2 int addNumbers int numberl int number2 int result numberl number2 return result Those Are the Basics At this point you have reviewed the basic essentials of C programming If this section was a breeze skim the next section to make sure that you re up to speed on the more advanced material If you 17 Chapter 1 struggled with this section you may want to obtain one of the fine introductory C books mentioned in Appendix D before continuing Diving Deeper into C Loops variables and conditionals are terrific building blocks but there is much more to learn The top ics covered next include many features that are designed to help C programmers with their code as well as a few features that are often more confusing than h
28. ge were addressed when C was designed Because C is based on C much of the syntax you ll see in this section will look familiar to you if are an experienced C programmer The two languages certainly have their differences though As evidence The C Programming Language by C creator Bjarne Stroustrup weighs in at 911 pages while Kernighan and Ritchie s The C Programming Language is a scant 274 pages So if you re a C programmer be on the lookout for new or unfamiliar syntax Chapter 1 The Obligatory Hello World In all its glory the following code is the simplest C program you re likely to encounter helloworld cpp include lt iostream gt int main int argc char argv std cout lt lt Hello World lt lt std endl return 0 This code as you might expect prints the message Hello World on the screen It is a simple program and unlikely to win any awards but it does exhibit several important concepts about the format of a C program Comments The first line of the program is a comment a message that exists for the programmer only and is ignored by the compiler In C there are two ways to delineate a comment In the preceding example two slashes indicate that whatever follows on that line is a comment helloworld cpp The same behavior this is to say none would be achieved by using a C style comment which is also valid in C C style comments start with and end with I
29. hange it unless you specifically tell it to Also when the foo function is done running the stack frame goes away and all of the variables declared within the function no longer take up memory The heap is an area of memory that is completely independent of the current function or stack frame You can put variables on the heap if you want them to exist even when the function in which they were declared has completed The heap is less structured than the stack You can think of it as just a pile of bits Your program can add new bits to the pile at any time or modify bits that are already in the pile 18 A Crash Course in C Dynamically Allocated Arrays Due to the way that the stack works the compiler must be able to determine at compile time how big each stack frame will be Since the stack frame size is predetermined you cannot declare an array with a variable size The following code will not compile because the arraySize is a variable not a constant int arraySize 8 int myVariableSizedArray arraySize This won t compile Because the entire array must go on the stack the compiler needs to know exactly what size it will be so variables aren t allowed However it is possible to specify the size of an array at run time by using dynamic memory and placing the array in the heap instead of the stack Some C compilers actually do support the preceding declaration but is not cur rently a part of the C specification
30. hod is called one of these blank employees will be populated with real data The mNext Slot data member keeps track of which blank employee is next in line to be populated The mNextEmployeeNumber data member keeps track of what employee number will be assigned to the new employee Database cpp Database cpp include lt iostream gt include lt stdexcept gt include Database h using namespace std namespace Records Database Database mNextSlot 0 mNextEmployeeNumber kFirstEmployeeNumber Database Database The Database constructor takes care of initializing the next slot and next employee number members to their starting values mNext Slot is initialized to zero so that when the first employee is added it will go into slot 0 of the mEmployees array 35 Chapter 1 Employee amp Database addEmployee string inFirstName string inLastName if mNextSlot gt kMaxEmployees cerr lt lt There is no more room to add the new employee lt lt endl throw exception Employee amp theEmployee mEmployees mNextSlot theEmployee setFirstName inFirstName theEmployee setLastName inLastName theEmployee setEmployeeNumber mNextEmployeeNumber theEmployee hire return theEmployee The addEmployee method fills in the next blank employee with actual information An initial check makes sure that the mEmployees array is not full and throws an exception
31. i Op a wmilexxteSlloes sak i if mEmployees i getIsHired mEmployees i display J The display methods all use a similar algorithm They loop through all nonblank employees and tell each employee to display itself to the console if the criterion for display matches DatabaseTest cpp A simple test for the basic functionality of the database follows DatabaseTest cpp include lt i0stream gt include Database h using namespace std using namespace Records int main int argc char argv Database myDB Employee amp empl myDB addEmployee Greg Wallis emp1 fire Employee amp emp2 myDB addEmployee Scott Kleper emp2 setSalary 100000 37 Chapter 1 Employee amp emp3 myDB addEmployee Nick Solter emp3 setSalary 10000 emp3 promote cout lt lt all employees lt lt endl cout ericiia myDB displayAll1 cout lt lt endl cout lt lt current employees lt lt endl cout lt lt endl myDB displayCurrent cout lt lt endl cout lt lt former employees lt lt endl cout lt lt endl myDB displayFormer The User Interface The final part of the program is a menu based user interface that makes it easy for users to work with the employee database Userlinterface cpp UserInterface cpp include lt i0stream gt include lt stdexcept gt include Database h using namespace std using namespace
32. igned long 1 5400 float Floating point and double precision float f 7 2 double numbers double d 7 2 char A single character char ch m bool true or false same as non 0 or 0 bool b true C does not provide a basic string type However a standard implementation of a string is provided as part of the standard library as described later in this chapter and in Chapter 13 Variables can be converted to other types by casting them For example an int can be cast to a bool C provides three ways of explicitly changing the type of a variable The first method is a holdover from C but is still the most commonly used The second method seems more natural at first but is rarely seen The third method is the most verbose but often considered the cleanest bool someBool bool someInt method 1 bool someBool bool someInt method 2 bool someBool static_cast lt bool gt someInt method 3 The result will be false if the integer was 0 and true otherwise In some contexts variables can be automatically cast or coerced For example a short can be automatically converted into a long because a long represents the same type of data with additional precision long someLong someShort no explicit cast needed When automatically casting variables you need to be aware of the potential loss of data For example casting a float to an int throws away information the fractional part of the number Many
33. ividual classes it is often useful to test them in isolation The following code includes a main function that performs some simple operations using the Employee class Once you are confi dent that the Employee class works you should remove or comment out this file so that you don t attempt to compile your code with multiple main functions EmployeeTest cpp include lt iostream gt include Employee h using namespace std using namespace Records int main int argc char argv cout lt lt Testing the Employee class lt lt endl 33 Chapter 1 Employee emp emp setFirstName Marni emp setLastName Kleper emp setEmployeeNumber 71 emp setSalary 50000 emp promote emp promote 50 emp hire emp display return 0 The Database Class The Database class uses an array to store Employee objects An integer called mNext Slot is used as a marker to keep track of the next unused array slot This method for storing objects is probably not ideal because the array is of a fixed size In Chapters 4 and 21 you will learn about data structures in the C standard library that you can use instead Database h Database h include lt iostream gt include Employee h namespace Records const int kMaxEmployees 100 const int kFirstEmployeeNumber 1000 Two constants are associated with the database The maximum number of employees is a constant because the re
34. more powerful Still it is important to know about the two most common ways of bu Enumerated Types ilding types so that you will recognize the syntax An integer really represents a value within a sequence the sequence of numbers Enumerated types let you define your own sequence example in a chess program you types as shown in the following c that they can never change int kPiece l int kPiecel int kPiecel int kPiecel const const const const etc ypeKing TypeQueen ypeRook TypePawn int myPiece kPieceTypeK This representation is fine but it c s so that you can declare variables with values in that sequence For could represent each piece as an int with constants for the piece ode The integers representing the types are marked const to indicate 0 1 1 2 3 1 ing an become dangerous Since the piece is just an int what would happen if another programmer added code to increment the value of the piece By adding one a king becomes a queen which really makes no sense Worse still someone could come in and give a piece a value of 1 which has no corresponding constant Enumerated types resolve these problems by tightly defining the range of values for a variable The fol lowing code declares a new type PieceT that has four possible values representing four of the chess pieces typedef enum kPieceTypeKing kPieceTypeQueen kPieceTypeRook kPieceTypePawn PieceT
35. most functions is that they take in zero or more parameters do some calculations and return a single result Sometimes however that pattern is broken You may be tempted to return two values or you may want the function to be able to change the value of one of the variables that were passed in In C the primary way to accomplish such behavior is to pass in a pointer to the variable instead of the variable itself The only problem with this approach is that it brings the messiness of pointer syntax into what is really a simple task In C there is an explicit mechanism for pass by reference Attaching amp to a type indicates that the variable is a reference It is still used as though it was a normal variable but behind the scenes it is really a pointer to the original variable Below are two implementations of an addone function The first will have no effect on the variable that is passed in because it is passed by value The second uses a reference and thus changes the original variable void addOne int i i Has no real effect because this is a copy of the original void addOne int amp i i Actually changes the original variable The syntax for the call to the addoOne function with an integer reference is no different than if the func tion just took an integer me mybe 7 p addone myInt Exceptions C is a very flexible language but not a particularly safe one The compiler will l
36. n this fashion C style comments are capable of spanning multiple lines The code below shows a C style comment in action or more appro priately inaction this is a multiline C style comment The compiler will ignore it Sales Comments are covered in detail in Chapter 7 Preprocessor Directives Building a C program is a three step process First the code is run through a preprocessor which recog nizes metainformation about the code Next the code is compiled or translated into machine readable object files Finally the individual object files are linked together into a single application Directives that are aimed at the preprocessor start with the character as in the line include lt iostream gt in the previous example In this case an include directive tells the preprocessor to take everything from the iostream header file and make it available to the current file The most common use of header files is to declare functions that will be defined elsewhere Remember a declaration tells the compiler how a func tion is called A definition contains the actual code for the function The iostream header declares the input and output mechanisms provided by C If the program did not include it it would be unable to perform its only task of outputting text A Crash Course in C In C included files usually end in h such as lt stdio h gt In C the suffix is omit ted for standard library headers such as lt io
37. oid AirlineTicket setPassengerName string inName mPassengerName inName int AirlineTicket getNumberOfMiles return mNumberOfMiles void AirlineTicket setNumberOfMiles int inMiles mNumberOfMiles inMiles A Crash Course in C bool AirlineTicket getHasEliteSuperRewardsStatus return fHasEliteSuperRewardsStatus void AirlineTicket setHasEliteSuperRewardsStatus bool inStatus fHasEliteSuperRewardsStatus inStatus The preceding example exposes you to the general syntax for creating and using classes Of course there is much more to learn Chapters 8 and 9 go into more depth about the specific C mechanisms for defining classes Your First Useful C Program The following program builds on the employee database example used earlier when discussing structs This time you will end up with a fully functional C program that uses many of the features discussed in this chapter This real world example includes the use of classes exceptions streams arrays names paces references and other language features An Employee Records System A program to manage a company s employee records needs to be flexible and have useful features The feature set for this program includes the following The ability to add an employee The ability to fire an employee The ability to promote an employee The ability to view all employees past and present The ability to view all current employees
38. onst can be used in several different ways in C All of its uses are related but there are subtle differences One of the authors has discovered that the subtleties of const make for excellent interview questions In Chapter 12 you will learn all of the ways that const can be used The following sections outline the most frequent uses Const Constants If you assumed that the keyword const has something to do with constants you have correctly uncov ered one of its uses In the C language programmers often use the preprocessor define mechanism to declare symbolic names for values that won t change during the execution of the program such as the version number In C programmers are encouraged to avoid define in favor of using const to define constants Defining a constant with const is just like defining a variable except that the compiler guarantees that code cannot change the value const float kVersionNumber 2 0 const string kProductName Super Hyper Net Modulator Const to Protect Variables In C you can cast a non const variable to a const variable Why would you want to do this It offers some degree of protection from other code changing the variable If you are calling a function that a coworker of yours is writing and you want to ensure that the function doesn t change the value of a parameter you pass in you can tell your coworker to have the function take a const parameter If the function attempts to change th
39. ork with strings of text in C There is the C style which represents strings as arrays of characters the C style which wraps that representation in an easier to use string type and the general class of nonstandard approaches C Style Strings A string of text like Hello World is internally represented as an array of characters with the character 0 representing the end of the string As you ve seen arrays and pointers are sometimes related You could use either one to represent a string as shown here char arrayString 20 Hello World char pointerString Hello World For the arrayString the compiler allocates space for 20 characters on the stack The first 13 characters in the array are filled in with H e etc ending with the character 0 The characters in positions 13 to 19 contain whatever random values happen to be in memory The 0 character tells code that uses the string where the content of the string ends Even though the array has a length of 20 functions that process or output the string should ignore everything after the 0 character For the pointerString the compiler allocates enough memory on the stack just to hold the pointer The pointer points to an area of memory that the compiler has set aside to hold the constant string Hello World In this string there is also a 0 character after the d character The C language provides a number of standard functions for working with
40. p address of operator skow at fp int myIntegerPointer amp 1 Points to the variable with the value 8 C has a special syntax for dealing with pointers to structures Technically if you have a pointer to a structure you can access its fields by first dereferencing it with then using the normal syntax as in the code that follows which assumes the existence of a function called getEmployee EmployeeT anEmployee getEmployee cout lt lt anEmployee salary lt lt endl A Crash Course in C This syntax is a little messy The gt arrow operator lets you perform both the dereference and the field access in one step The following code is equivalent to the preceding code but is easier to read EmployeeT anEmployee getEmployee cout lt lt anEmployee gt salary lt lt endl Normally when you pass a variable into a function you are passing by value If a function takes an inte ger parameter it is really a copy of the integer that you pass in Pointers to stack variables are often used in C to allow functions to modify variables in other stack frames essentially passing by reference By dereferencing the pointer the function can change the memory that represents the variable even though that variable isn t in the current stack frame This is less common in C because C has a better mech anism called references which is covered below Strings in C There are three ways to w
41. pragma is not standard across compilers we advocate not using it The main function main is of course where the program starts An int is returned from main indicating the result status of the program main takes two parameters argc gives the number of arguments passed to the program and argv contains those arguments Note that the first argument is always the name of the program itself 1 0 Streams If you re new to C and coming from a C background you re probably wondering what std cout is and what has been done with trusty old print While printf can still be used in C a much better input output facility is provided by the streams library Chapter 1 I O streams are covered in depth in Chapter 14 but the basics of output are very simple Think of an output stream as a laundry chute for data Anything you toss into it will be output appropriately std cout is the chute corresponding to the user console or standard out There are other chutes including std cerr which outputs to the error console The lt lt operator tosses data down the chute In the preceding example a quoted string of text is sent to standard out Output streams allow multiple data of varying types to be sent down the stream sequentially on a single line of code The following code outputs text followed by a number followed by more text std cout lt lt There are lt lt 219 lt lt ways I love you lt lt s
42. ringtest2 cpp include lt string gt include lt iostream gt using namespace std int main int argc char argv Slevin Shes PELLO string str2 World Stringi Geis syjerl qe 2 YW SETZ Coble lt lt lt sia as Y lt lt Biel lt lt Gel cout lt lt Str2 is lt lt str2 lt lt endl cout lt lt Str3 is lt lt str3 lt lt endl wie arry ello torii 1 cout lt lt str3 is what it should be lt lt endl else cout lt lt Hmmm return 0 The preceding examples show just a few of the many features of C strings Chapter 13 goes into fur ther detail str3 isn t what it should be lt lt endl A Crash Course in C Nonstandard Strings There are several reasons why many C programmers don t use C style strings Some programmers simply aren t aware of the string type because it was not always part of the C specification Others have discovered over the years that the C string doesn t provide the behavior they need and have developed their own string type Perhaps the most common reason is that development frameworks and operating systems tend to have their own way of representing strings such as the CString class in Microsoft s MFC Often this is for backward compatibility or legacy issues When starting a project in C it is very important to decide ahead of time how your group will represent strings References The pattern for
43. rs described below provide ways of evaluating expressions to result in a true or false Boolean value Switch Statements The switch statement is an alternate syntax for performing actions based on the value of a variable In switch statements the variable must be compared to a constant so the greater than if statements above could not be converted to switch statements Each constant value represents a case If the vari able matches the case the subsequent lines of code are executed until the break statement is reached You can also provide a default case which is matched if none of the other cases match switch statements are generally used when you want to do something based on the specific value of a variable as opposed to some test on the variable The following pseudocode shows a common use of the switch statement switch menuItem case kOpenMenultem Code to open a file break 12 A Crash Course in C case kSaveMenulItem Code to save a file break default Code to give an error message break If you omit the break statement the code for the subsequent case will be executed whether or not it matches This is sometimes useful but more frequently a source of bugs The Ternary Operator C has one operator that takes three arguments known as the ternary operator It is used as a shorthand conditional expression of the form if something then perform action otherwise perform some other action
44. stream gt Your favorite standard head ers from C still exist in C but with new names For example you can access the functionality from lt stdio h gt by including lt cstdio gt The table below shows some of the most common preprocessor directives Preprocessor Directive Functionality Common Uses include file define key value ifdef key ifndef key endif pragma The specified file is inserted into the code at the location of the directive Every occurrence of the specified key is replaced with the specified value Code within the ifdef if defined or ifndef if not defined blocks are conditionally included or omitted based on whether the specified value has been defined with define Varies from compiler to compiler Often allows the programmer to display a warning or error if the directive is reached during preprocessing Almost always used to include header files so that code can make use of functionality that is defined elsewhere Often used in C to define a constant value or a macro C provides a better mechanism for constants Macros are often dangerous so define is rarely used in C See Chapter 12 for details Used most frequently to protect against circular includes Each included file defines a value initially and surrounds the rest of its code with a ifndef and endif so that it won t be included multiple times Because usage of
45. strings which are described in the lt cstring gt header file The details of the standard library are not covered here because C pro vides a much cleaner and simpler way of working with strings C Strings C style strings are important to understand because they are still frequently used by C programmers However C includes a much more flexible string type The string type described by the lt string gt header file acts just like a basic type Just like I O streams the string type lives in the std package The example that follows shows how strings can be used just like character arrays 21 Chapter 1 22 stringtest cpp include lt string gt include lt iostream gt using namespace std int main int argc char euze string myString Hello World cout lt lt The value of myString is lt lt myString lt lt endl return 0 The magic of C strings is that you can use standard operators to work with them Instead of using a function like strcat in C to concatenate two strings you can simply use If you ve ever tried to use the operator to compare two C style strings you ve discovered that it doesn t work when used on C style strings is actually comparing the address of the character arrays not their contents With C strings actually compares two strings The example that follows shows some of the standard opera tors in use with C strings st
46. t greater than or greater than or gt equal to the right hand side Determines if the left hand side if i 3 4 equals the right hand side std cout lt lt i is 3 Don t confuse this with the assignment operator Table continued on following page 13 Chapter 1 Operator Description Usage t Not equals The result of if i 3 the statement is true if the std cout lt lt i is not 3 left hand side does not equal the right hand side Logical not Negates the if someBoolean true false status of a std cout lt lt someBoolean is false Boolean expression This is a unary operator amp amp Logical and The result if someBoolean amp amp someOtherBoolean is true if both parts of the std cout lt lt both are true expression are true Logical or The result is if someBoolean someOtherBoolean true if either part of the std cout lt lt at least one is true expression is true C uses short circuit logic when evaluating an expression That means that once the final result is cer tain the rest of the expression won t be evaluated For example if you are doing a logical or of several Boolean expressions as shown below the result is known to be true as soon as one of them is found to be true The rest won t even be checked bool result booll bool2 G gt 7 27 13 i 1 lt 2 In the example above if boo11 is found to be tr
47. t should remove it from the heap so that other variables can use the memory In C you use the delete command to do this delete myVariableSizedArray The brackets after delete indicate that you are deleting an array The C commands new and delete are similar to malloc and free from C The syntax of new and delete is simpler because you don t need to know how many bytes of memory are required Working with Pointers 20 There are other reasons to use heap memory besides dynamically allocating arrays You can put any variable in the heap by using a similar syntax int myIntegerPointer new int In this case the pointer points to just a single integer value To access this value you need to dereference the pointer Think of dereferencing as following the pointer s arrow to the actual value in the heap To set the value of the newly allocated heap integer you would use code like the following myIntegerPointer 8 Notice that this is not the same as setting myIntegerPointer to the value 8 You are not changing the pointer you are changing the memory that it points to If you were to reassign the pointer value it would point to the memory address 8 which is probably random garbage that will eventually make your program crash Pointers don t always point to heap memory You can declare a pointer that points to a variable on the stack even another pointer To get a pointer to a variable you use the am
48. td endl std endl represents an end of line character When the output stream encounters std end1 it will output everything that has been sent down the chute so far and move to the next line An alternate way of representing the end of a line is by using the n character The n character is an escape character which refers to a new line character Escape characters can be used within any quoted string of text The list below shows the most common escape characters n new line r carriage return t tab the backslash character Oococo oOo quotation mark Streams can also be used to accept input from the user The simplest way to do this is to use the gt gt operator with an input stream The std cin input stream accepts keyboard input from the user User input can be tricky because you can never know what kind of data the user will enter See Chapter 14 for a full explanation of how to use input streams Namespaces Namespaces address the problem of naming conflicts between different pieces of code For example you might be writing some code that has a function called foo One day you decide to start using a third party library which also has a foo function The compiler has no way of knowing which version of foo you are referring to within your code You can t change the library s function name and it would be a big pain to change your own Namespaces come to the rescue in such scenarios becaus
49. that the code to be executed comes first and the conditional check for whether or not to continue happens at the end In this way you can use a loop when you want a block of code to always be exe cuted at least once and possibly additional times based on some condition The example that follows will output This is silly once even though the condition will end up being false Migs a 1007 oma std cout lt lt This is silly lt lt std endl dseg P whibe Ii lt 5 The For Loop The for loop provides another syntax for looping Any for loop can be converted to a while loop and vice versa However the for loop syntax is often more convenient because it looks at a loop in terms of a starting expression an ending condition and a statement to execute at the end of every iteration In the following code i is initialized to 0 the loop will continue as long as i is less than 5 and at the end of every iteration i is incremented by 1 This code does the same thing as the while loop example but to some programmers it is easier to read because the starting value ending condition and per iteration statement are all visible on one line ong auae a Sh soe S e Gi Std an cCout Leas SS Niy 2 lt lt Std end Arrays Arrays hold a series of values all of the same type each of which can be accessed by its position in the array In C you must provide the size of the array when the array is declared You cannot give a vari
50. tions for the Employee class methods are shown here Employee cpp include lt iostream gt include Employee h using namespace std namespace Records Employee Employee mFirstName mLastName mEmployeeNumber 1 mSalary kDefaultStartingSalary fHired false The Employee constructor sets the initial values for the Employee s data members By default new employees have no name an employee number of 1 the default starting salary and a status of not hired void Employee promote int inRaiseAmount setSalary getSalary inRaiseAmount J void Employee demote int inDemeritAmount setSalary getSalary inDemeritAmount 31 Chapter 1 32 The promote and demote methods simply call the setSalary method with a new value Note that the default values for the integer parameters do not appear in the source file They only need to exist in the header void Employee hire fHired true void Employee fire fHired false The hire and fire methods just set the Hired data member appropriately void Employee display cou cou lt lt Salary lt lt getSalary lt lt endl lt lt endl cout lt lt Employee lt lt getLastName lt lt lt lt getFirstName lt lt endl Coutos e a lt lt endl cout lt lt fHired Current Employee Former Employee lt lt endl cout lt lt Employe
51. ts methods behaviors are declared Each data member and method is associated with a particular access level public protected or private These labels can occur in any order and can be repeated AirlineTicket h include lt string gt class AirlineTicket public AirlineTicket A Crash Course in C AirlineTicket int calculatePriceInDollars std string getPassengerName void setPassengerName std string inName int getNumberOfMiles void setNumberOfMiles int inMiles bool getHasEliteSuperRewardsStatus void setHasEliteSuperRewardsStatus bool inStatus private std string mPassengerName int mNumberOfMiles bool fHasEliteSuperRewardsStatus Wy The method that has the same name of the class with no return type is a constructor It is automatically called when an object of the class is created The method with a tilde character followed by the class name is a de The sample structor It is automatically called when the object is destroyed program that follows makes use of the class declared in the previous example This example shows the creation of a stack based AirlineTicket object as well as a heap based object AirlineTicketTest cpp include lt iostream gt include AirlineTicket h using namespace std int main int argc char argv AirlineTicket myTicket Stack based AirlineTicket my my Ticket setPassengerName Sherm
52. ue the entire expression must be true so the other parts aren t evaluated In this way the language saves your code from doing unnecessary work It can how ever be a source of hard to find bugs if the later expressions in some way influence the state of the pro gram for example by calling a separate function The following code shows a statement using amp amp that will short circuit after the second term because 1 always evaluates to true bool result booll amp amp 1 amp amp i gt 7 amp amp done Loops Computers are great for doing the same thing over and over C provides three types of looping structures The While Loop while loops let you perform a block of code repeatedly as long as an expression evaluates to true For example the following completely silly code will output This is silly five times Koe i Op while i lt 5 Siecle veowle lt lt Moe ais gallliky lt lt Siecle eievellls Ip 14 A Crash Course in C The keyword break can be used within a loop to immediately get out of the loop and continue execu tion of the program The keyword continue can be used to return to the top of the loop and reevaluate the while expression Both are often considered poor style because they cause the execution of a pro gram to jump around somewhat haphazardly The Do While Loop C also has a variation on the while loop called do while It works similarly to the while loop except
53. uld decide whether variables will be declared at the start of each function or on an as needed basis Variables can be declared without being given a value These undeclared variables generally end up with a semirandom value based on whatever is in memory at the time and are the source of countless bugs Variables in C can alternatively be assigned an initial value when they are declared The code that follows shows both flavors of variable declaration both using ints which represent integer values hellovariables cpp include lt iostream gt using namespace std int main int argc char argv int uninitializedint ne Uni tial zeding 2 75 cout lt lt uninitializedInt lt lt is a random value lt lt endl cout lt lt initializedInt lt lt was assigned an initial value lt lt endl return 0 A Crash Course in C When run this code will output a random value from memory for the first line and the number 7 for the second This code also shows how variables can be used with output streams The table that follows shows the most common variable types used in C Type Description Usage int Positive and negative integers range int i 7 depends on compiler settings short Short integer usually 2 bytes short s 13 long Long integer usually 4 bytes long 1 7 unsigned int Limits the preceding types to unsigned int i 2 unsigned short values gt 0 unsigned short s 23 unsigned long uns
54. ves but beware of overusing this shortcut In the extreme case if you declare that you re using every namespace known to humanity you re effectively eliminating namespaces entirely Name conflicts will again result if you are using two namespaces that contain the same names It is also important to know in which namespace your code is operating so that you don t end up accidentally calling the wrong version of a function You ve seen the namespace syntax before we used it in the Hello World program cout and endl are actually names defined in the std namespace We could have rewritten Hello World with the using directive as shown here Chapter 1 helloworld cpp include lt iostream gt using namespace std int main int argc char argv cout lt lt Hello World lt lt endl return 0 The using directive can also be used to refer to a particular item within a namespace For example if the only part of the std namespace that you intend to use is cout you can refer to it as follows using std cout Subsequent code can refer to cout without prepending the namespace but other items in the std namespace will still need to be explicit using std cout cout lt lt Hello World lt lt std endl Variables In C variables can be declared just about anywhere in your code and can be used anywhere in the cur rent block below the line where they are declared In practice your engineering group sho
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