Home

The C++ Language Tutorial

1. macro value LINE Integer value representing the current line in the source code file being compiled FILE A string literal containing the presumed name of the source file being compiled DATE A string literal in the form Mmm dd yyyy containing the date in which the compilation process began TIME A A string literal in the form hh mm ss containing the time at which the compilation process began An integer value All C compilers have this constant defined to some value If the compiler is fully cpluspluscompliant with the C standard its value is equal or greater than 199711L depending on the version of the standard they comply For example 136 eplusplus com 2008 All rights reserved The C Le guage Tutorial standard macro names include lt iostream gt using namespace std int main cout lt lt This is the line number lt lt LINE coute Eor sexe Y lt lt emia SW nl cout Les compilation began d DATE cole lt lt WV aie Y lt lt wii SW lp con SSEDheEconpilenmgqivesacdicplsoi salt eoe cout T cplusplus return 0 137 thas is the tine number 7 of filie home jay stdmacronames cpp Its compilation began Nov 1 2005 at TORIPE ZOR The compiler gives a cplusplus value of 1 eplusplus com 2008 All rights reserved 4 The ig n Tutorial C Standard Library Input Output with files C provides the following classe
2. bobby The first element pointed by bobby can be accessed either with the expression bobby 0 or the expression bobby Both are equivalent as has been explained in the section about pointers The second element can be accessed either with bobby 1 Or bobby 1 and so on You could be wondering the difference between declaring a normal array and assigning dynamic memory to a pointer as we have just done The most important difference is that the size of an array has to be a constant value which limits its size to what we decide at the moment of designing the program before its execution whereas the dynamic memory allocation allows us to assign memory during the execution of the program runtime using any variable or constant value as its size The dynamic memory requested by our program is allocated by the system from the memory heap However computer memory is a limited resource and it can be exhausted Therefore it is important to have some mechanism to check if our request to allocate memory was successful or not C provides two standard methods to check if the allocation was successful One is by handling exceptions Using this method an exception of type bad alloc is thrown when the allocation fails Exceptions are a powerful C feature explained later in these tutorials But for now you should know that if this exception is thrown and it is not handled by a specific handler the program execution is terminated 74
3. 4 The Be Tutorial The only new thing that we introduced is that the parameters of subtraction are variables instead of constants That is perfectly valid In this case the values passed to function subtraction are the values of x and y that are 5 and 3 respectively giving 2 as result The fourth case is more of the same Simply note that instead of vi 4 SUDE rac ETSN i E we could have written z subtraction x y 4 with exactly the same result I have switched places so you can see that the semicolon sign goes at the end of the whole statement It does not necessarily have to go right after the function call The explanation might be once again that you imagine that a function can be replaced by its returned value No Gu 2 N Functions with no type The use of void If you remember the syntax of a function declaration type name argumentl argument2 statement you will see that the declaration begins with a type that is the type of the function itself i e the type of the datum that will be returned by the function with the return statement But what if we want to return no value Imagine that we want to make a function just to show a message on the screen We do not need it to return any value In this case we should use the void type specifier for the function This is a special specifier that indicates absence of type void function example I m a function include lt iostream gt usin
4. When the buffer is flushed all the data contained in it is written to the physical medium if it is an output stream or simply freed if it is an input stream This process is called synchronization and takes place under any of the following circumstances e When the file is closed before closing a file all buffers that have not yet been flushed are synchronized and all pending data is written or read to the physical medium e When the buffer is full Buffers have a certain size When the buffer is full it is automatically synchronized e Explicitly with manipulators When certain manipulators are used on streams an explicit synchronization takes place These manipulators are flush and endl e Explicitly with member function sync Calling stream s member function sync which takes no parameters causes an immediate synchronization This function returns an int value equal to 1 if the stream has no associated buffer or in case of failure Otherwise if the stream buffer was successfully synchronized it returns 0 144 eplusplus com 2008 All rights reserved
5. eplusplus com 2008 All rights reserved 4 The ci Tutorial This exception method is the default method used by new and is the one used in a declaration like bobby new int 5 if it fails an exception is thrown The other method is known as nothrow and what happens when it is used is that when a memory allocation fails instead of throwing a bad alloc exception or terminating the program the pointer returned by new is a null pointer and the program continues its execution This method can be specified by using a special object called nothrow declared in header new as argument for new bobby new nothrow int 5 In this case if the allocation of this block of memory failed the failure could be detected by checking if bobby took a null pointer value int bobby bobby new nothrow int 5 if bobby 0 error assigning memory Take measures This nothrow method requires more work than the exception method since the value returned has to be checked after each and every memory allocation but I will use it in our examples due to its simplicity Anyway this method can become tedious for larger projects where the exception method is generally preferred The exception method will be explained in detail later in this tutorial Operators delete and delete Since the necessity of dynamic memory is usually limited to specific moments within a program once it is no longer needed it should
6. Assignment The assignment operator assigns a value to a variable a Do This statement assigns the integer value 5 to the variable a The part at the left of the assignment operator is known as the value left value and the right one as the rvalue right value The Ivalue has to be a variable whereas the rvalue can be either a constant a variable the result of an operation or any combination of these The most important rule when assigning is the right to left rule The assignment operation always takes place from right to left and never the other way a b This statement assigns to variable a the Ivalue the value contained in variable b the rvalue The value that was stored until this moment in a is not considered at all in this operation and in fact that value is lost Consider also that we are only assigning the value of b to a at the moment of the assignment operation Therefore a later change of b will not affect the new value of a For example let us have a look at the following code I have included the evolution of the content stored in the variables as comments assignment operator a 4 b 7 include lt iostream gt using namespace std int main dike d Je JUL ane Doe a 10 HU GEM OES i Ale H GEM list a b ef Sos Toa i yg Vi Ay DEN poub aive COUE La lp Come Uit Colle KK Jog return 0 This code will give us as result that the value contained in a is 4 and the o
7. However when typeid is applied to objects like a and b typeid yields their dynamic type i e the type of their most derived complete object If the type typeid evaluates is a pointer preceded by the dereference operator and this pointer has a null value typeid throws a bad typeid exception 132 eplusplus com 2008 All rights reserved 4 The enge Tutorial Preprocessor directives Preprocessor directives are lines included in the code of our programs that are not program statements but directives for the preprocessor These lines are always preceded by a hash sign 4 The preprocessor is executed before the actual compilation of code begins therefore the preprocessor digests all these directives before any code is generated by the statements These preprocessor directives extend only across a single line of code As soon as a newline character is found the preprocessor directive is considered to end No semicolon is expected at the end of a preprocessor directive The only way a preprocessor directive can extend through more than one line is by preceding the newline character at the end of the line by a backslash macro definitions define undef To define preprocessor macros we can use define Its format is define identifier replacement When the preprocessor encounters this directive it replaces any occurrence of identifier in the rest of the code by replacement This replacement can be
8. class mysequence T memblock N pubic void setmember int x T value T getmember int x r template lt class T int N gt void mysequence lt T N gt setmember int x T value memblock x value template lt class T int N gt T mysequence lt T N gt getmember int x return memblock x ine manni ET mysequence lt int 5 gt myints mysequence lt double 5 gt myfloats myints setmember 0 100 myfloats setmember 3 3 1416 cout lt lt myints getmember 0 lt lt n cout lt lt myfloats getmember 3 lt lt n return 0 It is also possible to set default values or types for class template parameters For example if the previous class template definition had been template lt class T char int N 10 gt class mysequence We could create objects using the default template parameters by declaring mysequence lt gt myseq Which would be equivalent to 118 eplusplus com 2008 All rights reserved 4 The cr e Tutorial mysequence lt char 10 gt myseq Templates and multiple file projects From the point of view of the compiler templates are not normal functions or classes They are compiled on demand meaning that the code of a template function is not compiled until an instantiation with specific template arguments is required At that moment when an instantiation is required the compiler generates a function specifically for those arguments from the
9. ppoly3 gt set_values 4 5 cout lt lt ppolyl gt area lt lt endl cout lt lt ppoly2 area lt lt endl cout lt lt ppoly3 gt area lt lt endl return 0 Now the three classes CPolygon CRectangle and CTriangle have all the same members width height set values and area The member function area has been declared as virtual in the base class because it is later redefined in each derived class You can verify if you want that if you remove this virtual keyword from the declaration of area within CPolygon and then you run the program the result will be 0 for the three polygons instead of 20 10 and 0 That is because instead of calling the corresponding area function for each object CRectangle area CTriangle area and CPolygon area respectively CPolygon area will be called in all cases since the calls are via a pointer whose type is CPolygon 108 eplusplus com 2008 All rights reserved 4 The ci Tutorial Therefore what the virtual keyword does is to allow a member of a derived class with the same name as one in the base class to be appropriately called from a pointer and more precisely when the type of the pointer is a pointer to the base class but is pointing to an object of the derived class as in the above example A class that declares or inherits a virtual function is called a polymorphic class Note that despite of its virtuality we have also been able t
10. Dereference operator We have just seen that a variable which stores a reference to another variable is called a pointer Pointers are said to point to the variable whose reference they store Using a pointer we can directly access the value stored in the variable which it points to To do this we simply have to precede the pointer s identifier with an asterisk which acts as dereference operator and that can be literally translated to value pointed by Therefore following with the values of the previous example if we write beth ted that we could read as beth equal to value pointed by ted beth would take the value 25 since ted is 1776 and the value pointed by 1776 is 25 ted memory beth You must clearly differentiate that the expression ted refers to the value 1776 while ted with an asterisk preceding the identifier refers to the value stored at address 1776 which in this case is 25 Notice the difference of including or not including the dereference operator I have included an explanatory commentary of how each of these two expressions could be read beth beth ted beth equal to ted 1776 ted beth equal to value pointed by ted 25 Notice the difference between the reference and dereference operators e amp isthe reference operator and can be read as address of e isthe dereference operator and can be read as value pointed by 64 eplusplus com 2008 All
11. addition 5 3 cout e Ihe result ts lt xr return 0 In order to examine this code first of all remember something said at the beginning of this tutorial a C program always begins its execution by the main function So we will begin there We can see how the main function begins by declaring the variable z of type int Right after that we see a call to a function called addition Paying attention we will be able to see the similarity between the structure of the call to the function and the declaration of the function itself some code lines above int addition int a int bh t f z addition 5 3 J The parameters and arguments have a clear correspondence Within the main function we called to addition passing two values 5 and 3 that correspond to the int a and int b parameters declared for function addition 41 eplusplus com 2008 All rights reserved 4 The enge Tutorial At the point at which the function is called from within main the control is lost by main and passed to function addition The value of both arguments passed in the call 5 and 3 are copied to the local variables int a and int b within the function Function addition declares another local variable int r and by means of the expression r a b it assigns to r the result of a plus b Because the actual parameters passed for a and b are 5 and 3 respectively the result is 8 The following line of code return r final
12. lt Mirvin mi Cir Jowsoxepasun p return 0 In this case we performed two insertions into cout in two different statements Once again the separation in different lines of code has been done just to give greater readability to the program since main could have been perfectly valid defined this way aes Jess 0 db cowe lt lt lt gere woe We cole lt lt V5 Vig el fene oroen Vp sain Op j We were also free to divide the code into more lines if we considered it more convenient int main gout lt lt Hello World cout e WAV cr CHpip Johetexepesint p return 0 And the result would again have been exactly the same as in the previous examples Preprocessor directives those that begin by are out of this general rule since they are not statements They are lines read and processed by the preprocessor and do not produce any code by themselves Preprocessor directives must be specified in their own line and do not have to end with a semicolon Comments Comments are parts of the source code disregarded by the compiler They simply do nothing Their purpose is only to allow the programmer to insert notes or descriptions embedded within the source code C supports two ways to insert comments line comment block comment The first of them known as line comment discards everything from where the pair of slash signs is found up to the end of that same line The second one known as block c
13. that appear in the previous example expression can be read as x pointed by x amp x address of x x y member y of object x x gt y member y of object pointed by x x y member y of object pointed by x equivalent to the previous one x 0 first object pointed by x x 1 second object pointed by x x n n 1 th object pointed by x Be sure that you understand the logic under all of these expressions before proceeding with the next sections If you have doubts read again this section and or consult the previous sections about pointers and data structures Classes defined with struct and union Classes can be defined not only with keyword class but also with keywords struct and union The concepts of class and data structure are so similar that both keywords struct and class can be used in C to declare classes i e structs can also have function members in C not only data members The only difference between both is that members of classes declared with the keyword struct have public access by default while members of classes declared with the keyword c1ass have private access For all other purposes both keywords are equivalent 93 eplusplus com 2008 All rights reserved The enge Tutorial The concept of unions is different from that of classes declared with struct and class since unions only store one data member at a time but nevertheless they are also classes and can th
14. therefore this catches also classes derived from exception like our myex object of class myexception All exceptions thrown by components of the C Standard library throw exceptions derived from this std exception class These are exception description bad_alloc thrown by new on allocation failure bad_cast thrown by dynamic_cast when fails with a referenced type bad exception thrown when an exception type doesn t match any catch bad typeid thrown by typeid ios base failureithrown by functions in the iostream library For example if we use the operator new and the memory cannot be allocated an exception of type bad alloc is thrown Ery int myarray new int 1000 catch bad alloc amp cout lt lt Error allocating memory lt lt endl It is recommended to include all dynamic memory allocations within a try block that catches this type of exception to perform a clean action instead of an abnormal program termination which is what happens when this type of exception is thrown and not caught If you want to force a bad_alloc exception to see it in action you can try to allocate a huge array On my system trying to allocate 1 billion ints threw a bad alloc exception Because bad alloc is derived from the standard base class exception we can handle that same exception by catching references to the exception class 125 eplusplus com 2008 All rights reserved d D lt The C
15. CPolygon poly would not be valid for the abstract base class we have just declared because tries to instantiate an object Nevertheless the following pointers Crolyoon ppolwir CPolwvoon bDpoly2 would be perfectly valid This is so for as long as CPolygon includes a pure virtual function and therefore it s an abstract base class However pointers to this abstract base class can be used to point to objects of derived classes Here you have the complete example 109 eplusplus com 2008 All rights reserved 4 The enge Tutorial abstract base class include lt iostream gt using namespace std class CPolygon protected int width height jeiullo babere vordiset i valuesik intan mint width a height b virtual int area void 0 hi class CRectangle public CPolygon jexslle babere int area void return width height E class CTriangle public CPolygon public int area void return width height 2 Jm int main CRectangle rect CTriangle trgl CPolygon ppolyl amp rect CPolygon ppolyz amp trgl ppolyl set values 4 5 ppoly2 set values 4 5 cout lt lt ppolyl gt area lt lt endl cout lt lt ppoly2 gt area lt lt endl return 0 20 10 If you review the program you will notice that we refer to objects of different but related classes using a unique type of pointer CPolygon This can be tremendously useful Fo
16. b amp a if b gt isitme a cout lt lt yes amp a is b return 0 It is also frequently used in operator member functions that return objects by reference avoiding the use of temporary objects Following with the vector s examples seen before we could have written an operator function similar to this one CVector amp CVector operator const CVector amp param x param x y param y return thie In fact this function is very similar to the code that the compiler generates implicitly for this class if we do not include an operator member function to copy objects of this class Static members A class can contain static members either data or functions Static data members of a class are also known as class variables because there is only one unique value for all the objects of that same class Their content is not different from one object of this class to another For example it may be used for a variable within a class that can contain a counter with the number of objects of that class that are currently allocated as in the following example 98 eplusplus com 2008 All rights reserved E The enge Tutorial static members in classes 7 include lt iostream gt 6 using namespace std class CDummy PUDINS Statie ane N eT mmy o ME EM exe army en ate int CDummy n 0 int main y CDummy a CDummy b 5 CDummy c new CDummy cout lt lt s n lt lt e
17. instead of narrow characters char we can precede the constant with the L prefix L This is a wide character string Wide characters are used mainly to represent non English or exotic character sets Boolean literals There are only two valid Boolean values true and false These can be expressed in C as values of type bool by using the Boolean literals true and false Defined constants define You can define your own names for constants that you use very often without having to resort to memory consuming variables simply by using the define preprocessor directive Its format is 19 eplusplus com 2008 All rights reserved 4 The Crt Lageugee Tutorial define identifier value For example define PI 3 14159 define NEWLINE n This defines two new constants PI and NEWLINE Once they are defined you can use them in the rest of the code as if they were any other regular constant for example defined constants calculate circumference 31 4159 include lt iostream gt using namespace std define PI 3 14159 define NEWLINE n int main double r 5 0 radius double circle eirele 2 se Pra r cout lt lt circle cout lt lt NEWLINE return 0 In fact the only thing that the compiler preprocessor does when it encounters define directives is to literally replace any occurrence of their identifier in the previous example these were PI and NEWLINE by the code to which
18. lt lt endl cout lt lt rectb area lt lt rectb area lt lt endl return 0 As you can see the result of this example is identical to the previous one But now we have removed the member function set_values and have included instead a constructor that performs a similar action it initializes the values of x and y with the parameters that are passed to it Notice how these arguments are passed to the constructor at the moment at which the objects of this class are created CRectangle rect 3 4 CRectangle rectb 5 6 Constructors cannot be called explicitly as if they were regular member functions They are only executed when a new object of that class is created You can also see how neither the constructor prototype declaration within the class nor the latter constructor definition include a return value not even void The destructor fulfills the opposite functionality It is automatically called when an object is destroyed either because its scope of existence has finished for example if it was defined as a local object within a function and the function ends or because it is an object dynamically assigned and it is released using the operator delete The destructor must have the same name as the class but preceded with a tilde sign and it must also return no value The use of destructors is especially suitable when an object assigns dynamic memory during its lifetime and at the moment of being destroyed
19. mycolor green mycolor red Enumerations are type compatible with numeric variables so their constants are always assigned an integer numerical value internally If it is not specified the integer value equivalent to the first possible value is equivalent to 0 and the following ones follow a 1 progression Thus in our data type colors t that we have defined above black would be equivalent to 0 blue would be equivalent to 1 green to 2 and so on 84 eplusplus com 2008 All rights reserved 4 The enge Tutorial We can explicitly specify an integer value for any of the constant values that our enumerated type can take If the constant value that follows it is not given an integer value it is automatically assumed the same value as the previous one plus one For example enum months t january 1 february march april may june july august september october november december y2k In this case variable y2k of enumerated type months_t can contain any of the 12 possible values that go from january to december and that are equivalent to values between 1 and 12 not between 0 and 11 since we have made january equal to 1 85 eplusplus com 2008 All rights reserved 4 The ci Tutorial Object Oriented Programming Classes I A class is an expanded concept of a data structure instead of holding only data it can hold both data and functions An object is an instantiation of a cl
20. on it followed by a variable of type int After this piece of code the variable myint will contain the numerical value 1204 stringstreams Enter price 22 25 include lt iostream gt Enter quantity 7 include lt string gt Total price 155 75 include lt sstream gt using namespace std int main String mystr float price 0 int quantity 0 cout lt lt Mangieere price Wp getline cin mystr stringstream mystr gt gt price cout lt lt Enter quantity 5 getline cin mystr stringstream mystr gt gt quantity cout lt lt Total price lt lt orice quantity lt lt endl return 0 In this example we acquire numeric values from the standard input indirectly Instead of extracting numeric values directly from the standard input we get lines from the standard input cin into a string object mystr and then we extract the integer values from this string into a variable of type int quantity 32 eplusplus com 2008 All rights reserved 4 The enge Tutorial Using this method instead of direct extractions of integer values we have more control over what happens with the input of numeric values from the user since we are separating the process of obtaining input from the user we now simply ask for lines with the interpretation of that input Therefore this method is usually preferred to get numerical values from the user in all programs that are intensive in user input
21. sqr set_side 4 rect convert sgr cout lt lt rect area return 0 In this example we have declared CRectangle as a friend of CSquare so that CRectangle member functions could have access to the protected and private members of CSquare more concretely to CSquare side which describes the side width of the square You may also see something new at the beginning of the program an empty declaration of class CSquare This is necessary because within the declaration of CRectangle we refer to CSquare as a parameter in convert The definition of CSquare is included later so if we did not include a previous empty declaration for CSquare this class would not be visible from within the definition of CRectangle Consider that friendships are not corresponded if we do not explicitly specify so In our example CRectangle is considered as a friend class by CSquare but CRectangle does not consider CSquare to be a friend so CRectangle can access the protected and private members of CSquare but not the reverse way Of course we could have declared also CSquare as friend of CRectangle if we wanted to Another property of friendships is that they are not transitive The friend of a friend is not considered to be a friend unless explicitly specified Inheritance between classes A key feature of C classes is inheritance Inheritance allows to create classes which are derived from other classes so that they automatically include some of i
22. 3 gt 6 evaluates to false true amp amp false 3 gt 6 evaluates to true true false oo Conditional operator The conditional operator evaluates an expression returning a value if that expression is true and a different one if the expression is evaluated as false Its format is condition resultl result2 If condition is true the expression will return result1 if it is not it will return result2 Wet poe 3 returns 3 since 7 is not equal to 5 mcbe3 o4 or 3 I returns 4 since 7 is egual to 542 Do SD returns the value of a since 5 is greater than 3 a gt b a b returns whichever is greater a or b conditional operator 7 include lt iostream gt using namespace std int main owe KK en return 0 In this example a was 2 and b was 7 so the expression being evaluated a gt b was not true thus the first value specified after the question mark was discarded in favor of the second value the one after the colon which was b with a value of 7 Comma operator The comma operator is used to separate two or more expressions that are included where only one expression is expected When the set of expressions has to be evaluated for a value only the rightmost expression is considered For example the following code a 9537 lue 25 eplusplus com 2008 All rights reserved 4 The enge Tutorial Would first assign the value 3 to b and
23. 33 eplusplus com 2008 All rights reserved 4 The cr e Tutorial Control Structures Control Structures A program is usually not limited to a linear sequence of instructions During its process it may bifurcate repeat code or take decisions For that purpose C provides control structures that serve to specify what has to be done by our program when and under which circumstances With the introduction of control structures we are going to have to introduce a new concept the compound statement or block A block is a group of statements which are separated by semicolons like all C statements but grouped together in a block enclosed in braces statementl statement2 statement3 Most of the control structures that we will see in this section require a generic statement as part of its syntax A statement can be either a simple statement a simple instruction ending with a semicolon or a compound statement several instructions grouped in a block like the one just described In the case that we want the statement to be a simple statement we do not need to enclose it in braces But in the case that we want the statement to be a compound statement it must be enclosed between braces forming a block Conditional structure if and else The if keyword is used to execute a statement or block only if a condition is fulfilled Its form is if condition statement Where condition is the expression that is
24. Language Tutorial bad alloc standard exception include lt iostream gt include lt exception gt using namespace std int main Cey int myarray new int 1000 catch exception amp e cout lt lt Standard exception lt lt e what lt lt endl return 0 126 eplusplus com 2008 All rights reserved 4 The Crt Lageugee Tutorial Type Casting Converting an expression of a given type into another type is known as type casting We have already seen some ways to type cast Implicit conversion Implicit conversions do not require any operator They are automatically performed when a value is copied to a compatible type For example short a 2000 sbsue lop b a Here the value of a has been promoted from short to int and we have not had to specify any type casting operator This is known as a standard conversion Standard conversions affect fundamental data types and allow conversions such as the conversions between numerical types short to int int to float double to int to or from bool and some pointer conversions Some of these conversions may imply a loss of precision which the compiler can signal with a warning This can be avoided with an explicit conversion Implicit conversions also include constructor or operator conversions which affect classes that include specific constructors or operator functions to perform conversions For example class A
25. also include some additional specific reserved keywords Very important The C language is a case sensitive language That means that an identifier written in capital letters is not equivalent to another one with the same name but written in small letters Thus for example the RESULT variable is not the same as the result variable or the Result variable These are three different variable identifiers Fundamental data types When programming we store the variables in our computer s memory but the computer has to know what kind of data we want to store in them since it is not going to occupy the same amount of memory to store a simple number than to store a single letter or a large number and they are not going to be interpreted the same way The memory in our computers is organized in bytes A byte is the minimum amount of memory that we can manage in C A byte can store a relatively small amount of data one single character or a small integer generally an integer between 0 and 255 In addition the computer can manipulate more complex data types that come from grouping several bytes such as long numbers or non integer numbers Next you have a summary of the basic fundamental data types in C as well as the range of values that can be represented with each one Name Description Size Range signed 128 to 127 h char Character or small integer 1byte unsigned 0 to 255 short int signed 32768 to 32767 short Short Integ
26. be freed so that the memory becomes available again for other requests of dynamic memory This is the purpose of the operator delete whose format is delete pointer deletes ooi er The first expression should be used to delete memory allocated for a single element and the second one for memory allocated for arrays of elements The value passed as argument to delete must be either a pointer to a memory block previously allocated with new or a null pointer in the case of a null pointer delete produces no effect 75 cplusplus com 2008 All rights reserved 4 The ci Tutorial rememb o matic How many numbers would you like to type 5 include lt iostream gt Enter number 75 include lt new gt Enter number 436 using namespace std Enter number 1067 Enter number 8 int main Enter number 32 You have entered 75 436 1067 8 32 abge abdo Jub aF cout lt lt How many numbers would you like to type Cia SS ae p new nothrow int i as ge 0 cout Error memory could not be allocated else for n 0 n i ntt cout lt lt Enter number Calin SS Terbo e cout lt lt You have entered for n 0 med ms Cole x pepe e UU We delete p return 0 Notice how the value within brackets in the new statement is a variable value entered by the user i not a constant value p new nothrow int i But the user could have entered a val
27. being evaluated If this condition is true statement is executed If it is false statement is ignored not executed and the program continues right after this conditional structure For example the following code fragment prints x is 100 only if the value stored in the x variable is indeed 100 if x 100 cout lt lt Mox is Que If we want more than a single statement to be executed in case that the condition is true we can specify a block using braces if x 100 oul lt lt x ais We Glo he ES X We can additionally specify what we want to happen if the condition is not fulfilled by using the keyword else Its form used in conjunction with i is if condition statementl else statement2 For example 34 eplusplus com 2008 All rights reserved 4 The Bs Tutorial if x 100 cout lt lt Ux as 100 else cout lt lt x 1s nob 100 prints on the screen x is 100 if indeed x has a value of 100 but if it has not and only if not it prints out x is not 100 The if else structures can be concatenated with the intention of verifying a range of values The following example shows its use telling if the value currently stored in x is positive negative or none of them i e zero if Se gt Oj coute lt We GIG ToxeXslabitab e p else if x lt 0 cout x is negative else Cowie we Use ale Ug Remember that in case that we want more than a single statement to be ex
28. block size read memory block size Where memory block is of type pointer to char char and represents the address of an array of bytes where the read data elements are stored or from where the data elements to be written are taken The size parameter is an integer value that specifies the number of characters to be read or written from to the memory block reading a complete binary file the complete file content is in memory include lt iostream gt include lt fstream gt using namespace std ifstream pos type size char memblock int main ifstream file example bin HOS tin oss binary ios tate ee GE eco Smowen size file tellg memblock new char size file seekg 0 ios beg file read memblock size file close cout the complete file content is in memory delete memblock else cout lt lt Unable to open file return 0 In this example the entire file is read and stored in a memory block Let s examine how this is done 143 eplusplus com 2008 All rights reserved 4 The Be Tutorial First the file is open with the ios ate flag which means that the get pointer will be positioned at the end of the file This way when we call to member tellg we will directly obtain the size of the file Notice the type we have used to declare variable size ifstream pos type size ifstream pos type is a specific type used for buffer and fi
29. class B X public BA m fy hg A a B b a Here a implicit conversion happened between objects of class A and class B because B has a constructor that takes an object of class A as parameter Therefore implicit conversions from A to B are allowed Explicit conversion C is a strong typed language Many conversions specially those that imply a different interpretation of the value require an explicit conversion We have already seen two notations for explicit type conversion functional and c like casting short a 2000 int b lo mE e c like cast notation lo int a functional notation The functionality of these explicit conversion operators is enough for most needs with fundamental data types However these operators can be applied indiscriminately on classes and pointers to classes which can lead to code that while being syntactically correct can cause runtime errors For example the following code is syntactically correct 127 cplusplus com 2008 All rights reserved E The iy Tutorial class type casting include lt iostream gt using namespace std class CDummy float abe aA class CAddition Ine a ye jorblleyl Latte p CAddition int a int b x a y b int result return x ty int main F CDummy d CAdoition padd padd CAddition amp d cout lt lt padd result return 0 The program declares a pointer to CAddition but then it ass
30. compound expression that can actually produce some effect In fact this statement performs the only action that generates a visible effect in our first program cout represents the standard output stream in C and the meaning of the entire statement is to insert a sequence of characters in this case the Hello World sequence of characters into the standard output stream which usually is the screen cout is declared in the iostream standard file within the std namespace so that s why we needed to include that specific file and to declare that we were going to use this specific namespace earlier in our code Notice that the statement ends with a semicolon character This character is used to mark the end of the statement and in fact it must be included at the end of all expression statements in all C programs one of the most common syntax errors is indeed to forget to include some semicolon after a statement return 0 The return statement causes the main function to finish return may be followed by a return code in our example is followed by the return code 0 A return code of 0 for the main function is generally interpreted as the program worked as expected without any errors during its execution This is the most usual way to end a C console program You may have noticed that not all the lines of this program perform actions when the code is executed There were lines containing only comments those beginning by There we
31. correspond to their literal binary value Data output operations on text files are performed in the same way we operated with cout writing on a text file file example txt include lt iostream gt This is a line include lt fstream gt This is another line using namespace std inte main F ofstream myfile example txt if myfile is open mytie lt lt nndca cem em myfile lt lt This is another line n myfile close else cout lt lt Unable to open file return 0 Data input from a file can also be performed in the same way that we did with cin 140 eplusplus com 2008 All rights reserved E The cr e Tutorial reading a text file This is a line include lt iostream gt This is another line include lt fstream gt include lt string gt using namespace std int main string line ifstream myfile example txt if myfile is open while myfile eof getline myfile line cout lt lt line lt lt endl myfile close else cout lt lt Unable to open file return 0 This last example reads a text file and prints out its content on the screen Notice how we have used a new member function called eof that returns true in the case that the end of the file has been reached We have created a while loop that finishes when indeed my ile eof becomes true i e the end of the file has been reached Checking stat
32. example of class CRectangle we could have declared the object rectb in addition to the object rect example one class two objects rect area 12 include lt iostream gt rectb area 30 using namespace std class CRectangle ant x ys jesse g void set values int int int area return x y woid CRectamgles set values ame a ant b x a y b int main CRectangle rect rectb rect set values 3 4 rectb set values 5 6 cout rect area rect area endl cout rectb area rectb area endl return 0 In this concrete case the class type of the objects to which we are talking about is CRectangle of which there are two instances or objects rect and rectb Each one of them has its own member variables and member functions Notice that the call to rect area does not give the same result as the call to rectb area This is because each object of class CRectangle has its own variables x and y as they in some way have also their own function members set value and area that each uses its object s own variables to operate That is the basic concept of object oriented programming Data and functions are both members of the object We no longer use sets of global variables that we pass from one function to another as parameters but instead we handle objects that have their own data and functions embedded as members Notice that we have not had to give any
33. having been modified Passing by reference is also an effective way to allow a function to return more than one value For example here is a function that returns the previous and next numbers of the first parameter passed more than one returning value Previous 99 Next 101 include iostream using namespace std void prevnext int x int amp prev int amp next prev Beale next x 1 int main ine x100 y Z prevnext x y z cout Previous y Next z return 0 Default values in parameters When declaring a function we can specify a default value for each of the last parameters This value will be used if the corresponding argument is left blank when calling to the function To do that we simply have to use the assignment operator and a value for the arguments in the function declaration If a value for that parameter is not passed when the function is called the default value is used but if a value is specified this default value is ignored and the passed value is used instead For example 48 z cplusplus com 2008 All rights reserved o 4 The enge Tutorial default values in functions include iostream E using namespace std int divide int a int b 2 abo 425 r a b return r int main cout lt lt divide 12 cout endi cout divide 20 4 return 0 As we can see in the body of the program there are two calls to func
34. identifier is any valid identifier and entities is the set of classes objects and functions that are included within the namespace For example namespace myNamespace inean b In this case the variables a and b are normal variables declared within a namespace called myNamespace In order to access these variables from outside the myNamespace namespace we have to use the scope operator For example to access the previous variables from outside myNamespace we can write myNamespace a myNamespace b The functionality of namespaces is especially useful in the case that there is a possibility that a global object or function uses the same identifier as another one causing redefinition errors For example namespaces 5 include iostream 3 1416 using namespace std namespace first int var 5 namespace second double var 3 1416 int main coub e Llrstiivar lt lt endl cout lt lt second var lt lt endl return 0 In this case there are two global variables with the same name var One is defined within the namespace first and the other one in second No redefinition errors happen thanks to namespaces 120 eplusplus com 2008 All rights reserved 4 The Be Tutorial using The keyword using is used to introduce a name from a namespace into the current declarative region For example using E include iostream Zt LBS using namespace std 10 3 1416 namespac
35. included with your compiler if you have doubts on how to compile a C console program The previous program is the typical program that programmer apprentices write for the first time and its result is the printing on screen of the Hello World sentence It is one of the simplest programs that can be written in C but it already contains the fundamental components that every C program has We are going to look line by line at the code we have just written my first program in C This is a comment line All lines beginning with two slash signs are considered comments and do not have any effect on the behavior of the program The programmer can use them to include short explanations or observations within the source code itself In this case the line is a brief description of what our program is include lt iostream gt Lines beginning with a hash sign are directives for the preprocessor They are not regular code lines with expressions but indications for the compiler s preprocessor In this case the directive include lt iostream gt tells the preprocessor to include the iostream standard file This specific file iostream includes the declarations of the basic standard input output library in C and it is included because its functionality is going to be used later in the program using namespace std All the elements of the standard C library are declared within what is called a namespace the namespace with the name
36. is enclosed between double quotes because it is a constant string of characters Whenever we want to use constant strings of characters we must enclose them between double quotes so that they can be clearly distinguished from variable names For example these two sentences have very different results cout lt lt Hello prints Hello cout lt lt Hello prints the content of Hello variable The insertion operator lt lt may be used more than once in a single statement cout lt lt Hallo lt lt I am ccm Ctt statement This last statement would print the message Hello I am a C statement on the screen The utility of repeating the insertion operator lt lt is demonstrated when we want to print out a combination of variables and constants or more than one variable cout lt lt Hello I am lt lt age lt lt years old and my zipcode is lt lt zipcode If we assume the age variable to contain the value 24 and the zipcode variable to contain 90064 the output of the previous statement would be Hello I am 24 years old and my zipcode is 90064 It is important to notice that cout does not add a line break after its output unless we explicitly indicate it therefore the following statements 29 eplusplus com 2008 All rights reserved 4 The ci Tutorial cout lt lt This is a sentence W cout This is another sentence will be shown on the screen one following th
37. is the number three expressed as a floating point numeric literal The default type for floating point literals is double If you explicitly want to express a float or long double numerical literal you can use the f or 1 suffixes respectively Se Ans Sin long double 6 02e23f H float Any of the letters that can be part of a floating point numerical constant e 1 can be written using either lower or uppercase letters without any difference in their meanings Character and string literals There also exist non numerical constants like zZ Vio Hello world Pow do you dob The first two expressions represent single character constants and the following two represent string literals composed of several characters Notice that to represent a single character we enclose it between single quotes and to express a string which generally consists of more than one character we enclose it between double quotes 7 When writing both single character and string literals it is necessary to put the quotation marks surrounding them to distinguish them from possible variable identifiers or reserved keywords Notice the difference between these two expressions x alone would refer to a variable whose identifier is x whereas x enclosed within single quotation marks would refer to the character constant x Character and string literals have certain peculiarities like the escape codes These are special characters that are diff
38. one is billy 1 and therefore the third one is billy 2 By this same reason its last element is billy 4 Therefore if we write billy 5 we would be accessing the sixth element of billy and therefore exceeding the size of the array In C it is syntactically correct to exceed the valid range of indices for an array This can create problems since accessing out of range elements do not cause compilation errors but can cause runtime errors The reason why this is allowed will be seen further ahead when we begin to use pointers At this point it is important to be able to clearly distinguish between the two uses that brackets have related to arrays They perform two different tasks one is to specify the size of arrays when they are declared and the second one is to specify indices for concrete array elements Do not confuse these two possible uses of brackets with arrays 55 eplusplus com 2008 All rights reserved 4 The enge Tutorial aoe aliyil declaration of a new array lopli Le Was access to an element of the array If you read carefully you will see that a type specifier always precedes a variable or array declaration while it never precedes an access Some other valid operations with arrays billy 0 a Tome da TIS b billy at2 billy billy a billy 2 5 arrays example 12206 include lt iostream gt using namespace std bie sewise Dp quies 2 Wile d 3029730 5
39. parameters in any of the calls to rect area or rectb area Those member functions directly used the data members of their respective objects rect and rectb Constructors and destructors Objects generally need to initialize variables or assign dynamic memory during their process of creation to become operative and to avoid returning unexpected values during their execution For example what would happen if in the previous example we called the member function area before having called function set values Probably we would have gotten an undetermined result since the members x and y would have never been assigned a value In order to avoid that a class can include a special function called constructor which is automatically called whenever a new object of this class is created This constructor function must have the same name as the class and cannot have any return type not even void We are going to implement CRectangle including a constructor 88 eplusplus com 2008 All rights reserved 4 The ci Tutorial example class constructor rect area 12 include lt iostream gt rectb area 30 using namespace std class CRectangle int width height puple CRectangle int int int area return width height CRectangle CRectangle int a int b width a height b int main CRectangle rect 3 4 CRectangle rectb 5 6 cout lt lt rect area lt lt rect area
40. price and in the second one we have not The difference is seen when we access the members dollars and yens of an object of this type For an object of the first type it would be book price dollars book price yens whereas for an object of the second type it would be book dollars book yens Once again I remind you that because it is a union and not a struct the members dollars and yens occupy the same physical space in the memory so they cannot be used to store two different values simultaneously You can set a value for price in dollars or in yens but not in both Enumerations enum Enumerations create new data types to contain something different that is not limited to the values fundamental data types may take Its form is the following enum enumeration name valuel value2 value3 object names For example we could create a new type of variable called color to store colors with the following declaration enum colors t black blue green cyan red purple yellow white Notice that we do not include any fundamental data type in the declaration To say it somehow we have created a whole new data type from scratch without basing it on any other existing type The possible values that variables of this new type color t may take are the new constant values included within braces For example once the colors t enumeration is declared the following expressions will be valid colors myeolor mycolor blue if
41. rights reserved 4 The enge Tutorial Thus they have complementary or opposite meanings A variable referenced with amp can be dereferenced with Earlier we performed the following two assignment operations andy 25 ted amp andy Right after these two statements all of the following expressions would give true as result andy 25 amp andy 1776 ted 1776 ted 25 The first expression is quite clear considering that the assignment operation performed on andy was andy 25 The second one uses the reference operator which returns the address of variable andy which we assumed it to have a value of 1776 The third one is somewhat obvious since the second expression was true and the assignment operation performed on ted was ted amp andy The fourth expression uses the dereference operator that as we have just seen can be read as value pointed by and the value pointed by ted is indeed 25 So after all that you may also infer that for as long as the address pointed by ted remains unchanged the following expression will also be true ted andy Declaring variables of pointer types Due to the ability of a pointer to directly refer to the value that it points to it becomes necessary to specify in its declaration which data type a pointer is going to point to It is not the same thing to point to a char as to point to an int ora float The declaration of pointers follows this format type
42. set of functions or operators 76 eplusplus com 2008 All rights reserved 4 The enge Tutorial Data structures We have already learned how groups of sequential data can be used in C But this is somewhat restrictive since in many occasions what we want to store are not mere sequences of elements all of the same data type but sets of different elements with different data types Data structures A data structure is a group of data elements grouped together under one name These data elements known as members can have different types and different lengths Data structures are declared in C using the following syntax struct structure name member typei member namel1 member type2 member name2 member type3 member name3 object names where structure name is a name for the structure type object name can be a set of valid identifiers for objects that have the type of this structure Within braces there is a list with the data members each one is specified with a type and a valid identifier as its name The first thing we have to know is that a data structure creates a new type Once a data structure is declared a new type with the identifier specified as structure name is created and can be used in the rest of the program as if it was any other type For example Eee produce int weight float price product apple product banana melon We have first declared a structure type cal
43. since otherwise the function would perform an infinite recursive loop in which once it arrived to 0 it would continue multiplying by all the negative numbers probably provoking a stack overflow error on runtime This function has a limitation because of the data type we used in its design long for more simplicity The results given will not be valid for values much greater than 10 or 15 depending on the system you compile it Declaring functions Until now we have defined all of the functions before the first appearance of calls to them in the source code These calls were generally in function main which we have always left at the end of the source code If you try to repeat some of the examples of functions described so far but placing the function main before any of the other functions that were called from within it you will most likely obtain compiling errors The reason is that to be able to call a function it must have been declared in some earlier point of the code like we have done in all our examples But there is an alternative way to avoid writing the whole code of a function before it can be used in main or in some other function This can be achieved by declaring just a prototype of the function before it is used instead of the entire definition This declaration is shorter than the entire definition but significant enough for the compiler to determine its return type and the types of its parameters Its form is 5
44. sty xm public vVoidiset values Ime ane int area void rect Declares a class i e a type called CRectangle and an object i e a variable of this class called rect This class contains four members two data members of type int member x and member y with private access because private is the default access level and two member functions with public access set_values and area of which for now we have only included their declaration not their definition Notice the difference between the class name and the object name In the previous example CRectangle was the class name i e the type whereas rect was an object of type CRectangle It is the same relationship int and a have in the following declaration 86 eplusplus com 2008 All rights reserved 4 The ig n Tutorial int a where int is the type name the class and a is the variable name the object After the previous declarations of CRectangle and rect we can refer within the body of the program to any of the public members of the object rect as if they were normal functions or normal variables just by putting the object s name followed by a dot and then the name of the member All very similar to what we did with plain data structures before For example rect set values 354 myarea rect area The only members of rect that we cannot access from the body of our program outside the class are x and y since they have private acce
45. the class template parameter Template specialization If we want to define a different implementation for a template when a specific type is passed as template parameter we can declare a specialization of that template For example let s suppose that we have a very simple class called mycontainer that can store one element of any type and that it has just one member function called increase which increases its value But we find that when it stores an element of type char it would be more convenient to have a completely different implementation with a function member uppercase so we decide to declare a class template specialization for that type template specialization 8 include lt iostream gt J using namespace std class template template class T class mycontainer T element papine mycontainer T arg element arg T increase return t element class template specialization template lt gt class mycontainer char char element pupies mycontainer char arg element arg char uppercase if element gt a amp amp element lt z element A a return element int main mycontainer lt int gt myint 7 mycontainer lt char gt mychar j cout lt lt myint increase lt lt endl cout lt lt mychar uppercase lt lt endl return 0 This is the syntax used in the class template specialization template lt gt class mycontainer
46. the member yours year is a valid variable of type int and mine title is a valid variable of type string The objects mine and yours can also be treated as valid variables of type movies t for example we have passed them to the function printmovie as we would have done with regular variables Therefore one of the most important advantages of data structures is that we can either refer to their members individually or to the entire structure as a block with only one identifier 78 eplusplus com 2008 All rights reserved 4 The enge Tutorial Data structures are a feature that can be used to represent databases especially if we consider the possibility of building arrays of them array Of Structures iueuewe ql include lt iostream gt Enter year 1 include lt string gt Enter title include lt sstream gt Enter year 1 using namespace std Enter title Enter year I define N MOVIES 3 You have ente Blade Runner Matrix 1999 Taxi Driver Struct movies min String Enele int year films N MOVIES void printmovie movies t movie int main string mystr mmt for n 0 n N MOVIES n cout lt lt Enter title gt getline cin films n title cout lt lt Enter year getline cin mystr stringstream mystr gt gt films n year cout lt lt nYou have entered these movies n for n 0 n N MOVIES n printmovie films n return 0 vo
47. the new capabilities included in ANSI C especially those released prior to the publication of the standard This tutorial is thought to be followed with modern compilers that support at least on some degree ANSI C specifications I encourage you to get one if yours is not adapted There are many options both commercial and free Compilers The examples included in this tutorial are all console programs That means they use text to communicate with the user and to show their results eplusplus com 2008 All rights reserved Es 4 The enge Tutorial All C compilers support the compilation of console programs Check the user s manual of your compiler for more info on how to compile them eplusplus com 2008 All rights reserved 4 The cr e Tutorial Basics of C Structure of a program Probably the best way to start learning a programming language is by writing a program Therefore here is our first program my first program inm CFF Hello World include lt iostream gt using namespace std int main cout lt lt Hellen World return 0 The first panel shows the source code for our first program The second one shows the result of the program once compiled and executed The way to edit and compile a program depends on the compiler you are using Depending on whether it has a Development Interface or not and on its version Consult the compilers section and the manual or help
48. to declare all objects of that class according to the constructor prototypes you defined for the class 91 eplusplus com 2008 All rights reserved 4 The ci Tutorial class CExample public ine a De CExample int n int m a n b m semel wabdbeuedby 0 4L Gees jg Here we have declared a constructor that takes two parameters of type int Therefore the following object declaration would be correct CExample ex 2 3 But CExample ex Would not be correct since we have declared the class to have an explicit constructor thus replacing the default constructor But the compiler not only creates a default constructor for you if you do not specify your own It provides three special member functions in total that are implicitly declared if you do not declare your own These are the copy constructor the copy assignment operator and the default destructor The copy constructor and the copy assignment operator copy all the data contained in another object to the data members of the current object For CExample the copy constructor implicitly declared by the compiler would be something similar to CExample CExample const CExample amp rv a rv a b rv b c rv c Therefore the two following object declarations would be correct CExample ex 2 3 CExample ex2 ex copy constructor data copied from ex Pointers to classes It is perfectly valid to create pointers that point to c
49. very little interaction with the user if any at all Using the standard input and output library we will be able to interact with the user by printing messages on the screen and getting the user s input from the keyboard C uses a convenient abstraction called streams to perform input and output operations in sequential media such as the screen or the keyboard A stream is an object where a program can either insert or extract characters to from it We do not really need to care about many specifications about the physical media associated with the stream we only need to know it will accept or provide characters sequentially The standard C library includes the header file iostream where the standard input and output stream objects are declared Standard Output cout By default the standard output of a program is the screen and the C stream object defined to access it iS cout cout s used in conjunction with the insertion operator which is written as lt lt two less than signs cout lt lt Output sentence prints Output sentence on screen cou ce 1210 prints number 120 on screen cout lt lt x prints the content of x on screen The lt lt operator inserts the data that follows it into the stream preceding it In the examples above it inserted the constant string Output sentence the numerical constant 120 and variable x into the standard output stream cout Notice that the sentence in the first instruction
50. void pointer is a special type of pointer that can point to somewhere without a specific type One refers to the value stored in the pointer itself and the other to the type of data it points to Pointers to functions C allows operations with pointers to functions The typical use of this is for passing a function as an argument to another function since these cannot be passed dereferenced In order to declare a pointer to a function we have to declare it like the prototype of the function except that the name of the function is enclosed between parentheses and an asterisk is inserted before the name 72 eplusplus com 2008 All rights reserved P The enge Tutorial pointer to functions 8 include iostream using namespace std ine addition int ar int D return atb aine Sionee cae aime el aee dej return a b int operation int x int y int functoce int 396 Woe yp gq functbocall x vi return g int main HUME ils ny int minus aint nt subtraction m operation 7 5 addition n operation 20 m minus SUD EMESSSTIIT return 0 In the example minus is a pointer to a function that has two parameters of type int It is immediately assigned to point to the function subtraction all in a single line ine 4 minus Gime nt subtraction 73 cplusplus com 2008 All rights reserved 4 The cr e Tutorial Dyn
51. we want to release the memory that the object was allocated 89 eplusplus com 2008 All rights reserved 4 The ci Tutorial example on constructors and destructors rect area 12 include lt iostream gt rectb area 30 using namespace std class CRectangle int width height foulbiaes CRectangle int int CRectangle int area return width height J CRectangle CRectangle int a int b width new int height new int width a height b CRectangle CRectangle delete width delete height int main CRectangle rect 3 4 rectb 5 6 cout rect area rect area endl cout rectb area rectb area endl return 0 Overloading Constructors Like any other function a constructor can also be overloaded with more than one function that have the same name but different types or number of parameters Remember that for overloaded functions the compiler will call the one whose parameters match the arguments used in the function call In the case of constructors which are automatically called when an object is created the one executed is the one that matches the arguments passed on the object declaration 90 eplusplus com 2008 All rights reserved 4 The enge Tutorial overloading class constructors rect area 12 include lt iostream gt rectb area 25 using namespace std class CRectangl
52. zero character And in order to express a hexadecimal number we have to precede it with the characters 0x zero x For example the following literal constants are all equivalent to each other 75 decimal 0113 H octal 0x4b hexadecimal All of these represent the same number 75 seventy five expressed as a base 10 numeral octal numeral and hexadecimal numeral respectively Literal constants like variables are considered to have a specific data type By default integer literals are of type int However we can force them to either be unsigned by appending the u character to it or long by appending 1 75 JL aset g5u unsigned int JSL long nowi unsigned long In both cases the suffix can be specified using either upper or lowercase letters Floating Point Numbers They express numbers with decimals and or exponents They can include either a decimal point an e character that expresses by ten at the Xth height where X is an integer value that follows the e character or both a decimal point and an e character 17 cplusplus com 2008 All rights reserved 4 The Bs Tutorial SMS Hi Sha IUIUS E0979 1 2561102 x 0223 LOSS Wi Wats vx Os 3 0 Hit Sis These are four valid numbers with decimals expressed in C The first number is PI the second one is the number of Avogadro the third is the electric charge of an electron an extremely small number all of them approximated and the last one
53. 1 eplusplus com 2008 All rights reserved 4 The ig n Tutorial type name argument typel argument type2 It is identical to a function definition except that it does not include the body of the function itself i e the function statements that in normal definitions are enclosed in braces and instead of that we end the prototype declaration with a mandatory semicolon The parameter enumeration does not need to include the identifiers but only the type specifiers The inclusion of a name for each parameter as in the function definition is optional in the prototype declaration For example we can declare a function called protofunction with two int parameters with any of the following declarations ine EOvcorunic tions Ane hasty Ine feKeXeleso ol P ink prototunction int 305 Anyway including a name for each variable makes the prototype more legible declaring functions prototypes Type a number 0 to exit 9 include lt iostream gt Number is odd using namespace std Type a number 0 to exit 6 Number is even iwiexel vexelel Cases e E Type a number 0 to exit 1030 void even int a Number is even Type a number 0 to exit 0 int main Number is even aioe ube do cout lt lt Type a number 0 to exit Ein E abe Sockel Gb S while i 0 return 0 void odd int a sis eso N00 coue lt lt verse is oclh Were else even a void even int a if a 2 0 c
54. Control StTUCtUFO6S 2502s ccsccsusacctscccaceasausvesssssasccaasuananassscaccesauanaesdscasccosiuanen tastes TRA IUE PURO E OVE EAE UAR UE EXTR REG 34 Control Str ctUres cette ete E ehe E E E EUR EUR RER YE Baa ERE a aS AA E YEAR e aUe ee Re obe sex VE AUN RE 34 F lictions 1 orici etri a ad a Ord Ho ds xdv etna doa vun doe xd pude va duce ius eor pod ERAS 41 FU lictions Il secenario ette d dev tet eleven ed avvia tau au etx lev ux tav ute vs vo ted ev inne 47 Compound data types 5 1 voies oo presso so Era sio ova aa Soy ea 8o Oy yag a Sopa Yo SEU YR TONEN EEEN Feb oa do E Ya RES Rag RR DOR 54 hic Cp MM 54 Character Sequences rrise rriorse aai a aa a aa raina eap Taa PERENE RE arisi 60 eE E A E E A E E E T E E AN E E E E 63 Dynamic MOM OF RE 74 D ta Str rUCtU ES TEE 77 Other Data TVD6S ric otecser oen que dias cie i doeet a ees eo eraran ee eer a rarae rip Es ce ETE 82 Object Oriented Programmitng 452 5512 eno ao io annua so nra ooa regna so nau ph Io nasa a SU Na saa Soa NER ERR SO Y RR RR SN NRR RR OR 86 Classes I ise te ie Gs I eM NIME I E RU IE LE 86 Classes Il Secssicssesezcescssssunecovsgneed R AN peus etes eau etes du vases de eg a V eet dU saan du RES DU REESE seta 95 Friendship and inheritance sisse enne nnn nennen nn niani s ares setis n nass essi tasa sans nnns 100 Polymorpbistmi eic onte iei et Rode eco toten aces Romeo
55. ZE Line control line When we compile a program and some error happen during the compiling process the compiler shows an error message with references to the name of the file where the error happened and a line number so it is easier to find the code generating the error The 1ine directive allows us to control both things the line numbers within the code files as well as the file name that we want that appears when an error takes place Its format is line number filename Where number is the new line number that will be assigned to the next code line The line numbers of successive lines will be increased one by one from this point on filename is an optional parameter that allows to redefine the file name that will be shown For example 135 eplusplus com 2008 All rights reserved 4 The Crt Lageugee Tutorial line 20 assigning variable aliene YER This code will generate an error that will be shown as error in file assigning variable line 20 Error directive error This directive aborts the compilation process when it is found generating a compilation the error that can be specified as its parameter ifndef cplusplus error A C compiler is required endif This example aborts the compilation process if the macro name __ cplusplus is not defined this macro name is defined by default in all C compilers Source file inclusion include This directive has also been used ass
56. a class derived from mother that we defined as class daughter protected mother This would set protected as the maximum access level for the members of daughter that it inherited from mother That is all members that were public in mother would become protected in daughter Of course this would not restrict daughter to declare its own public members That maximum access level is only set for the members inherited from mother If we do not explicitly specify any access level for the inheritance the compiler assumes private for classes declared with class keyword and public for those declared with struct What is inherited from the base class In principle a derived class inherits every member of a base class except e its constructor and its destructor e its operator members e its friends Although the constructors and destructors of the base class are not inherited themselves its default constructor i e its constructor with no parameters and its destructor are always called when a new object of a derived class is created or destroyed If the base class has no default constructor or you want that an overloaded constructor is called when a new derived object is created you can specify it in each constructor definition of the derived class derived constructor name parameters base constructor name parameters For example 104 eplusplus com 2008 All rights reserved 4 The enge Tutorial
57. ading the addition operator This function can be called either implicitly using the operator or explicitly using the function name ap lag c a operator b Both expressions are equivalent Notice also that we have included the empty constructor without parameters and we have defined it with an empty block wecicone D dL je This is necessary since we have explicitly declared another constructor CVector int int And when we explicitly declare any constructor with any number of parameters the default constructor with no parameters that the compiler can declare automatically is not declared so we need to declare it ourselves in order to be able to construct objects of this type without parameters Otherwise the declaration 96 eplusplus com 2008 All rights reserved 4 The Bs Tutorial o Vie GIO e included in main would not have been valid Anyway I have to warn you that an empty block is a bad implementation for a constructor since it does not fulfill the minimum functionality that is generally expected from a constructor which is the initialization of all the member variables in its class In our case this constructor leaves the variables x and y undefined Therefore a more advisable definition would have been something similar to this CVector x0 ys0 I which in order to simplify and show only the point of the code I have not included in the example As well as a c
58. amic Memory Until now in all our programs we have only had as much memory available as we declared for our variables having the size of all of them to be determined in the source code before the execution of the program But what if we need a variable amount of memory that can only be determined during runtime For example in the case that we need some user input to determine the necessary amount of memory space The answer is dynamic memory for which C integrates the operators new and delete Operators new and new In order to request dynamic memory we use the operator new new is followed by a data type specifier and if a sequence of more than one element is required the number of these within brackets It returns a pointer to the beginning of the new block of memory allocated Its form is pointer new type pointer new type number of elements The first expression is used to allocate memory to contain one single element of type type The second one is used to assign a block an array of elements of type type where number of elements is an integer value representing the amount of these For example int bobby bobby new int 5 In this case the system dynamically assigns space for five elements of type int and returns a pointer to the first element of the sequence which is assigned to bobby Therefore now bobby points to a valid block of memory with space for five elements of type int int _ _
59. an expression a statement a block or simply anything The preprocessor does not understand C it simply replaces any occurrence of identifier by replacement define TABLE SIZE 100 int tablel TABLE SIZE int table2 TABLE SIZE After the preprocessor has replaced TABLE SIZE the code becomes equivalent to int tabilel 100 int tabte2 100 This use of define as constant definer is already known by us from previous tutorials but define can work also with parameters to define function macros define getmax a b a gt b a b This would replace any occurrence of getmax followed by two arguments by the replacement expression but also replacing each argument by its identifier exactly as you would expect if it was a function function macro 5 include lt iostream gt 7 using namespace std define getmax a b a gt b a b int main int x 5 y y getmax x 2 cout lt lt y lt lt endl cout lt lt getmax 7 x lt lt endl return 0 Defined macros are not affected by block structure A macro lasts until it is undefined with the undef preprocessor directive 133 cplusplus com 2008 All rights reserved 4 The enge Tutorial define TABLE SIZE 100 int tablel TABLE SIZE fundef TABLE SIZE define TABLE SIZE 200 int table2 TABLE SIZE This would generate the same code as int tabilel 100 int tabile2 200 Function macro definitions accept two special ope
60. an object of this class to store two integer values of type int with the values 115 and 36 we would write mypair lt int gt myobject 115 36 this same class would also be used to create an object to store any other type mypair lt double gt myfloats 3 0 2 18 The only member function in the previous class template has been defined inline within the class declaration itself In case that we define a function member outside the declaration of the class template we must always precede that definition with the template lt gt prefix class templates 100 include lt iostream gt using namespace std template lt class T gt class mypair Tome de pupie mypair T first T second a first b second T getmax r template lt class T gt T mypair lt T gt getmax T retval retval a gt b a b return retval int main Ty adam smit c t lOO E EE cout lt lt myobject getmax return 0 Notice the syntax of the definition of member function getmax 116 eplusplus com 2008 All rights reserved E The Bs Tutorial template lt class T gt T mypair lt T gt getmax Confused by so many T s There are three T s in this declaration The first one is the template parameter The second T refers to the type returned by the function And the third T the one between angle brackets is also a requirement It specifies that this function s template parameter is also
61. and height of different objects of type CRectangle which are private members Notice that neither in the declaration of duplicate nor in its later use in main have we considered duplicate a member of class CRectangle It isn t It simply has access to its private and protected members without being a member The friend functions can serve for example to conduct operations between two different classes Generally the use of friend functions is out of an object oriented programming methodology so whenever possible it is better to use members of the same class to perform operations with them Such as in the previous example it would have been shorter to integrate duplicate within the class CRectangle 100 eplusplus com 2008 All rights reserved 4 The Bs Tutorial Friend classes Just as we have the possibility to define a friend function we can also define a class as friend of another one granting that first class access to the protected and private members of the second one friend class 16 include lt iostream gt using namespace std class CSquare class CRectangle int width height public int area return width height void convert CSquare a class CSquare private int side public vou1dasetesuides untea side a friend class CRectangle void CRectangle convert CSquare a width a side height a side int main CSquare sqr CRectangle rect
62. ants that represent entire strings of characters have already showed up several times These are specified enclosing the text to become a string literal between double quotes For example the result iss 60 eplusplus com 2008 All rights reserved 4 The Crt ig n Tutorial is a constant string literal that we have probably used already Double quoted strings are literal constants whose type is in fact a null terminated array of characters So string literals enclosed between double quotes always have a null character 0 automatically appended at the end Therefore we can initialize the array of char elements called myword with a null terminated sequence of characters by either one of these two methods char myword ff Misa reget DLs NSU Mirela UNO cate char myword Hello In both cases the array of characters myword is declared with a size of 6 elements of type char the 5 characters that compose the word Hello plus a final null character 0 which specifies the end of the sequence and that in the second case when using double quotes it is appended automatically Please notice that we are talking about initializing an array of characters in the moment it is being declared and not about assigning values to them once they have already been declared In fact because this type of null terminated arrays of characters are regular arrays we have the same restrictions that we have with any ot
63. asily achieved by declaring all functions prototypes at the beginning of a program 53 eplusplus com 2008 All rights reserved 4 The ci Tutorial Compound data types Arrays An array is a series of elements of the same type placed in contiguous memory locations that can be individually referenced by adding an index to a unique identifier That means that for example we can store 5 values of type int in an array without having to declare 5 different variables each one with a different identifier Instead of that using an array we can store 5 different values of the same type int for example with a unique identifier For example an array to contain 5 integer values of type int called billy could be represented like this 0 1 2 3 4 billy PP d int where each blank panel represents an element of the array that in this case are integer values of type int These elements are numbered from 0 to 4 since in arrays the first index is always 0 independently of its length Like a regular variable an array must be declared before it is used A typical declaration for an array in C is type name elements where type is a valid type like int float name is a valid identifier and the elements field which is always enclosed in square brackets specifies how many of these elements the array has to contain Therefore in order to declare an array called billy as the one shown in the above diagram it
64. ass In terms of variables a class would be the type and an object would be the variable Classes are generally declared using the keyword class with the following format class class_name access specifier 1 member1 access_specifier 2 member2 object_names Where class_name is a valid identifier for the class object names is an optional list of names for objects of this class The body of the declaration can contain members that can be either data or function declarations and optionally access specifiers All is very similar to the declaration on data structures except that we can now include also functions and members but also this new thing called access specifier An access specifier is one of the following three keywords private public Or protected These specifiers modify the access rights that the members following them acquire e private members of a class are accessible only from within other members of the same class or from their friends e protected members are accessible from members of their same class and from their friends but also from members of their derived classes e Finally public members are accessible from anywhere where the object is visible By default all members of a class declared with the c1ass keyword have private access for all its members Therefore any member that is declared before one other class specifier automatically has private access For example class CRectangle Amt
65. at can take any of the following values ios beg offset counted from the beginning of the stream ios cur joffset counted from the current position of the stream pointer ios end offset counted from the end of the stream The following example uses the member functions we have just seen to obtain the size of a file 142 eplusplus com 2008 All rights reserved 4 The ci Tutorial obtaining file size size is 40 bytes include lt iostream gt include lt fstream gt using namespace std int main long begin end ifstream myfile example txt begin myfile tellg myfile seekg 0 ios end end myfile tellg myfile close cout lt lt size asi lt lt end begin lt lt bytes n return 0 Binary files In binary files to input and output data with the extraction and insertion operators lt lt and gt gt and functions like getline is not efficient since we do not need to format any data and data may not use the separation codes used by text files to separate elements like space newline etc File streams include two member functions specifically designed to input and output binary data sequentially write and read The first one write is a member function of ostream inherited by ofstream And read is a member function of istream that is inherited by ifstream Objects of class fstream have both members Their prototypes are write memory
66. aught by other handlers if it is specified at last 123 eplusplus com 2008 All rights reserved 4 The enge Tutorial mue oq code here catch int param cout lt lt int exception catch char param cout lt lt char exception Catch cout lt lt default exception In this case the last handler would catch any exception thrown with any parameter that is neither an int nora char After an exception has been handled the program execution resumes after the try catch block not after the throw statementl It is also possible to nest try catch blocks within more external try blocks In these cases we have the possibility that an internal catch block forwards the exception to its external level This is done with the expression throw with no arguments For example eyi Eey A code here cateh GINE N di throw cabo oe 4 cout lt lt Exception occurred Exception specifications When declaring a function we can limit the exception type it might directly or indirectly throw by appending a throw suffix to the function declaration float myfunction char parem throw int This declares a function called myfunction which takes one agument of type char and returns an element of type float The only exception that this function might throw is an exception of type int If it throws an exception with a different type either directly or indirectly it cannot be ca
67. ay Access publicprotected private members of the same class yes yes yes members of derived classesyes yes no not members yes no no Where not members represent any access from outside the class such as from main from another class or from a function In our example the members inherited by CRectangle and CTriangle have the same access permissions as they had in their base class CPolygon 103 eplusplus com 2008 All rights reserved 4 The enge Tutorial CPolygon width protected access CRectangle width protected access CPolygon set values public access CRectangle set values public access This is because we have used the pub1ic keyword to define the inheritance relationship on each of the derived classes class CRectangle public CPolygon This public keyword after the colon denotes the maximum access level for all the members inherited from the class that follows it in this case CPolygon Since public is the most accessible level by specifying this keyword the derived class will inherit all the members with the same levels they had in the base class If we specify a more restrictive access level like protected all public members of the base class are inherited as protected in the derived class Whereas if we specify the most restricting of all access levels private all the base class members are inherited as private For example if daughter was
68. before the variable identifier a or after it a Although in simple expressions like a or a both have exactly the same meaning in other expressions in which the result of the increase or decrease operation is evaluated as a value in an outer expression they may have an important difference in their meaning In the case that the increase operator is used as a prefix a the value is increased before the result of the expression is evaluated and therefore the increased value is considered in the outer expression in case that it is used as a suffix a the value stored in a is increased after being evaluated and therefore the value stored before the increase operation is evaluated in the outer expression Notice the difference Example 1 Example 2 B 3 B 3 A B IA B A contains 4 B contains 4 A contains 3 B contains 4 In Example 1 B is increased before its value is copied to A While in Example 2 the value of B is copied to A and then B is increased Relational and equality operators gt lt gt lt In order to evaluate a comparison between two expressions we can use the relational and equality operators The result of a relational operation is a Boolean value that can only be true or false according to its Boolean result We may want to compare two expressions for example to know if they are equal or if one is greater than the other is Here is a list of the relational and equality ope
69. bjects of type CBase pba and pbb to a pointer object of type CDerived but only the first one is successful Notice their respective initializations new CDerived new CBase CBase pba CBase pbb Even though both are pointers of type CBase pba points to an object of type CDerived while pbb points to an object of type cBase Thus when their respective type castings are performed using dynamic cast pba is pointing to a full object of class CbDerived whereas pbb is pointing to an object of class CBase which is an incomplete object of class CDerived When dynamic cast cannot cast a pointer because it is not a complete object of the required class as in the second conversion in the previous example it returns a null pointer to indicate the failure If dynamic cast is used to convert to a reference type and the conversion is not possible an exception of type bad cast is thrown instead dynamic cast can also cast null pointers even between pointers to unrelated classes and can also cast pointers of any type to void pointers void 129 eplusplus com 2008 All rights reserved 4 The cr e Tutorial static cast static cast can perform conversions between pointers to related classes not only from the derived class to its base but also from a base class to its derived This ensures that at least the classes are compatible if the proper object is converted but no safety check is performed during runtime to che
70. case n where n is a variable or ranges case 1 3 because they are not valid C constants If you need to check ranges or values that are not constants use a concatenation of if and else if statements 40 eplusplus com 2008 All rights reserved 4 The enge Tutorial Functions I Using functions we can structure our programs in a more modular way accessing all the potential that structured programming can offer to us in C A function is a group of statements that is executed when it is called from some point of the program The following is its format type name parameterl parameter2 statements where type is the data type specifier of the data returned by the function e name is the identifier by which it will be possible to call the function parameters as many as needed Each parameter consists of a data type specifier followed by an identifier like any regular variable declaration for example int x and which acts within the function as a regular local variable They allow to pass arguments to the function when it is called The different parameters are separated by commas e statements is the function s body It is a block of statements surrounded by braces Here you have the first function example function example The result is 8 include iostream using namespace std int addition int a int p aoho 485 r atb return r inec eme abate ag z
71. ce std int main String mystring mystring This is the initial string content cout lt lt mystring lt lt endl mystring This is a different string content cout mystring endl return 07 For more details on C strings you can have a look at the string class reference 16 eplusplus com 2008 All rights reserved 4 The ci Tutorial Constants Constants are expressions with a fixed value Literals Literals are used to express particular values within the source code of a program We have already used these previously to give concrete values to variables or to express messages we wanted our programs to print out for example when we wrote a 5 the 5 in this piece of code was a literal constant Literal constants can be divided in Integer Numerals Floating Point Numerals Characters Strings and Boolean Values Integer Numerals TS 707 cS They are numerical constants that identify integer decimal values Notice that to express a numerical constant we do not have to write quotes nor any special character There is no doubt that it is a constant whenever we write 1776 in a program we will be referring to the value 1776 In addition to decimal numbers those that all of us are used to use every day C allows the use as literal constants of octal numbers base 8 and hexadecimal numbers base 16 If we want to express an octal number we have to precede it with a 0
72. char First of all notice that we precede the class template name with an emptytemplate lt gt parameter list This is to explicitly declare it as a template specialization 117 eplusplus com 2008 All rights reserved 4 The ig n Tutorial But more important than this prefix is the lt char gt specialization parameter after the class template name This specialization parameter itself identifies the type for which we are going to declare a template class specialization char Notice the differences between the generic class template and the specialization template class T class mycontsiner I template lt gt class mycontainer char The first line is the generic template and the second one is the specialization When we declare specializations for a template class we must also define all its members even those exactly equal to the generic template class because there is no inheritance of members from the generic template to the specialization Non type parameters for templates Besides the template arguments that are preceded by the class or typename keywords which represent types templates can also have regular typed parameters similar to those found in functions As an example have a look at this class template that is used to contain sequences of elements sequence template 100 include lt iostream gt 3 1416 using namespace std template lt class T int N gt
73. char is a one byte long type The value returned by sizeof is a constant so it is always determined before program execution Other operators Later in these tutorials we will see a few more operators like the ones referring to pointers or the specifics for object oriented programming Each one is treated in its respective section Precedence of operators When writing complex expressions with several operands we may have some doubts about which operand is evaluated first and which later For example in this expression a gt 5 7 3 2 26 cplusplus com 2008 All rights reserved 4 The cH agure Tutorial we may doubt if it really means With a result of Ci Or a B 7 2 with a result of 0 The correct answer is the first of the two expressions with a result of 6 There is an established order with the priority of each operator and not only the arithmetic ones those whose preference come from mathematics but for all the operators which can appear in C From greatest to lowest priority the priority order is as follows Level Operator Description Grouping E E Left to i P right O gt dynamic cast static cast Left to 2 reinterpret cast const cast typeid postfix right sizeof new delete unary prefix 3 Pare indirection and reference Right to pointers left To unary sign operator Right to 4 type type casting left m OPEN Lef
74. ck if the object being converted is in fact a full object of the destination type Therefore it is up to the programmer to ensure that the conversion is safe On the other side the overhead of the type safety checks of dynamic cast is avoided class CBase class CDerived public CBase CBase a new CBase Gheruvedaessbexsbatauegcast eDennived oa m This would be valid although b would point to an incomplete object of the class and could lead to runtime errors if dereferenced static cast can also be used to perform any other non pointer conversion that could also be performed implicitly like for example standard conversion between fundamental types double d 3 14159265 amt Mcteibnrelre sibimet Or any conversion between classes with explicit constructors or operator functions as described in implicit conversions above reinterpret cast reinterpret cast converts any pointer type to any other pointer type even of unrelated classes The operation result is a simple binary copy of the value from one pointer to the other All pointer conversions are allowed neither the content pointed nor the pointer type itself is checked It can also cast pointers to or from integer types The format in which this integer value represents a pointer is platform specific The only guarantee is that a pointer cast to an integer type large enough to fully contain it is granted to be able to be cast back to a valid pointer The conversions
75. constructors and derived classes mother no parameters include lt iostream gt daughter int parameter using namespace std mother int parameter class mother son int parameter jeiblodbiberg mother cout lt lt mother no parameters Nn mother int a cout lt lt mother int parameter Wn J class daughter public mother papine daughter int a cout lt lt daughter int parameter n n class son public mother polos e son int a mother a cout lt lt son int parameter n n hg int main daughter cynthia 0 son daniel 0 return 0 Notice the difference between which mother s constructor is called when a new daughter object is created and which when it is a son object The difference is because the constructor declaration of daughter and son daughter int a nothing specified call default son int a mother a constructor specified call this Multiple inheritance In C it is perfectly possible that a class inherits members from more than one class This is done by simply separating the different base classes with commas in the derived class declaration For example if we had a specific class to print on screen COutput and we wanted our classes CRectangle and CTriangle to also inherit its members in addition to those of CPolygon we could write class CRectangle public CPolygon public COutput elass Clrvanche public Elson Wee Utt here is the compl
76. cplusplus com C Language Tutorial Written by Juan Souli Last revision June 2007 Available online at http www cplusplus com doc tutorial The online version is constantly revised and may contain corrections and changes 4 The ci Tutorial This document and its content is copyright of cplusplus com cplusplus com 2008 All rights reserved Any redistribution or reproduction of part or all of the content in any form is prohibited other than to print a personal copy of the entire document or download it to a local hard disk without modifying its content in any way including but not limited to this copyright notice You may not except with express written permission from cplusplus com distribute the content of this document Nor may you transmit it or store it in any other website or other form of electronic retrieval system eplusplus com 2008 All rights reserved 4 The enge Tutorial Table of contents UEL TISCALI LIU DOLI UMUUUTEMMUEET 3 bier Ts ror Pc 5 Terieesrete eoa 5 BaSiCs Of o m 7 Structure OF a proie M 7 Ege ERE CNP o TP 11 oriri M 17 Blur lmee 21 Basic Te Vi OG TV e V RRRRRRRRRRRRRRRRRRRRRRREMMEEEEEMEEEEMMMMMMMMMMN 29
77. d by a valid variable identifier For example 12 eplusplus com 2008 All rights reserved 4 The enge Tutorial alie lp float mynumber These are two valid declarations of variables The first one declares a variable of type int with the identifier a The second one declares a variable of type float with the identifier mynumber Once declared the variables a and mynumber can be used within the rest of their scope in the program If you are going to declare more than one variable of the same type you can declare all of them in a single statement by separating their identifiers with commas For example inte ely Joly Nel This declares three variables a b and c all of them of type int and has exactly the same meaning as int s ime By ant cr The integer data types char short long and int can be either signed or unsigned depending on the range of numbers needed to be represented Signed types can represent both positive and negative values whereas unsigned types can only represent positive values and zero This can be specified by using either the specifier signed or the specifier unsigned before the type name For example unsigned short int NumberOfSisters Signed int MyAccountBalance By default if we do not specify either signed or unsigned most compiler settings will assume the type to be signed therefore instead of the second declaration above we could have written int MyAccountBalance wi
78. d operate with any of these elements as if they were standard variables of their respective types apple weight apple price banana weight banana price melon weight melon price Each one of these has the data type corresponding to the member they refer to apple weight banana weight and melon weight are of type int while apple price banana price and melon price are of type float Let s see a real example where you can see how a structure type can be used in the same way as fundamental types example about structures include lt iostream gt include lt string gt include lt sstream gt using namespace std struct moves mind string castles int year mine yours void printmovie movies t movie int main string mystr mine title 2001 A Space Odyssey mine year 1968 Colts lt lt Winters Celes We getline cin yours title cout lt lt Enter year 7 getline cin mystr stringstream mystr gt gt yours year cout lt lt My favorite movie is n printmovie mine Come lt lt Umuml sous es in Up printmovie yours return 0 void printmovie movies t movie cout lt lt movie title Come lt lt W lt lt moviles yec lt lt wy WE Enter title Alien Enter year 1979 My favorite movie is 2001 A Space Odyssey 1968 Andiyours alls Alien 1979 The example shows how we can use the members of an object as regular variables For example
79. ddition Also it would have been impossible to use the variable z directly within function addition since this was a variable local to the function main Hinclude lt iostream h gt int Integer Char aCharacter char string 20 Global variables unsigned int Humber fsons unsigned short Age float AHumber Another ne Localvariahles cout lt lt Enter your age cin Age Instructions Therefore the scope of local variables is limited to the same block level in which they are declared Nevertheless we also have the possibility to declare global variables These are visible from any point of the code inside and outside all functions In order to declare global variables you simply have to declare the variable outside any function or block that means directly in the body of the program And here is another example about functions 43 eplusplus com 2008 All rights reserved 4 The enge Tutorial function example The first result is 5 include iostream The second result is 5 using namespace std The third result is 2 The fourth result is 6 buma hbleneseeieacaueim Simic Gu aee le alone aad r a b return r int main Int x5 Ey d z subtraction 7 2 Come lt lt Mine mihian resili sie W X m lt lt UNIQUE cout lt lt ihe secondi result is uk Subtraction ESSERI couci ariet iirdiresulti ris a Sut onae EN z 4 subtraction x y cout lt lt UTr
80. dynamically allocated 111 eplusplus com 2008 All rights reserved P The enge Tutorial dynamic allocation and polymorphism 20 include lt iostream gt 10 using namespace std class CPolygon protected int width height public VOU Seta values aint vals mint B width a height b virtual int area void 0 void printarea void cout lt lt this gt area lt lt endl Me class CRectangle public CPolygon public int area void return width height he class CTriangle public CPolygon pupie int area void return width height 2 Ig int main CPolygon ppolyl new CRectangle CPolygon ppoly2 new CTriangle ppolyl set values 4 5 ppoly2 set values 4 5 ppolyl printarea ppoly2 printarea delete ppolyl delete ppoly2 return 0 Notice that the ppoly pointers CPolygon ppolyl new CRectangle CPolygon ppoly2 new CTriangle are declared being of type pointer to CPolygon but the objects dynamically allocated have been declared having the derived class type directly 112 eplusplus com 2008 All rights reserved 4 The enge Tutorial Advanced concepts Templates Function templates Function templates are special functions that can operate with generic types This allows us to create a function template whose functionality can be adapted to more than one type or class without repeating the entire cod
81. e cin gt gt age The first statement declares a variable of type int called age and the second one waits for an input from cin the keyboard in order to store it in this integer variable cin can only process the input from the keyboard once the RETURN key has been pressed Therefore even if you request a single character the extraction from cin will not process the input until the user presses RETURN after the character has been introduced You must always consider the type of the variable that you are using as a container with cin extractions If you request an integer you will get an integer if you request a character you will get a character and if you request a string of characters you will get a string of characters 30 eplusplus com 2008 All rights reserved 4 The enge Tutorial i o example Please enter an integer value 702 The value you entered is 702 and its double is include lt iostream gt 1404 using namespace std int main ant X cout Please enter an integer value eng 29 abe cout The value you entered is i cout lt lt eich ilies double as Eco Mcr return 0 The user of a program may be one of the factors that generate errors even in the simplest programs that use cin like the one we have just seen Since if you request an integer value and the user introduces a name which generally is a string of characters the result may cause your program to misope
82. e int width height pupie CRectangle CRectangle int int int area void return width height CRectangle CRectangle width 5 height 5 CRectangle CRectangle int a int b width a height b int main CRectangle rect 3 4 CRectangle rectb cout lt lt rect area lt lt rect area lt lt endl cout lt lt rectb area lt lt rectb area lt lt endl return 0 In this case rectb was declared without any arguments so it has been initialized with the constructor that has no parameters which initializes both width and height with a value of 5 Important Notice how if we declare a new object and we want to use its default constructor the one without parameters we do not include parentheses CRectangle rectb Pe aee CRectangle rectb wrong Default constructor If you do not declare any constructors in a class definition the compiler assumes the class to have a default constructor with no arguments Therefore after declaring a class like this one class CExample mouse e int eir lei ep void multiply int n int m an bsm c a b Jj The compiler assumes that CExample has a default constructor so you can declare objects of this class by simply declaring them without any arguments CExample ex But as soon as you declare your own constructor for a class the compiler no longer provides an implicit default constructor So you have
83. e accepts them of type 1oat The compiler knows which one to call in each case by examining the types passed as arguments when the function is called If it is called with two ints as its arguments it calls to the function that has two int parameters in its prototype and if it is called with two floats it will call to the one which has two 1oat parameters in its prototype In the first call to operate the two arguments passed are of type int therefore the function with the first prototype is called This function returns the result of multiplying both parameters While the second call passes two arguments of type float so the function with the second prototype is called This one has a different behavior it divides one parameter by the other So the behavior of a call to operate depends on the type of the arguments passed because the function has been overloaded Notice that a function cannot be overloaded only by its return type At least one of its parameters must have a different type inline functions The inline specifier indicates the compiler that inline substitution is preferred to the usual function call mechanism for a specific function This does not change the behavior of a function itself but is used to suggest to the compiler that the code generated by the function body is inserted at each point the function is called instead of being inserted only once and perform a regular call to it which generally involves some additional ov
84. e conducted with them the others make no sense in the world of pointers But both addition and subtraction have a different behavior with pointers according to the size of the data type to which they point When we saw the different fundamental data types we saw that some occupy more or less space than others in the memory For example let s assume that in a given compiler for a specific machine char takes 1 byte short takes 2 bytes and 1ong takes 4 Suppose that we define three pointers in this compiler char mychar Isynveyiexc Seti ASlloXe ee long mylong and that we know that they point to memory locations 1000 2000 and 3000 respectively So if we write mychart myshort mylongt mychar aS you may expect would contain the value 1001 But not so obviously myshort would contain the value 2002 and mylong would contain 3004 even though they have each been increased only once The reason is that when adding one to a pointer we are making it to point to the following element of the same type with which it has been defined and therefore the size in bytes of the type pointed is added to the pointer 69 eplusplus com 2008 All rights reserved 4 The enge Tutorial 1000 1001 CREE 2000 2001 2002 2003 LL myshort 3000 3001 3002 3003 3004 3005 3006 3007 es mylong This is applicable both when adding and subtracting any number to a pointer It would happen exactly the
85. e first int x e 5 align NE KOL namespace second double x 3 1416 double y 2 7183 int main wisubmey ebrei gop using second y cout x endl cout lt lt y lt lt endl cout lt lt first y lt lt endl cout lt lt second x lt lt endl return 0 Notice how in this code x without any name qualifier refers to first x whereas y refers to second y exactly as our using declarations have specified We still have access to first y and second x using their fully qualified names The keyword using can also be used as a directive to introduce an entire namespace using 5 include iostream 10 using namespace std 3 1416 Eo WARS Namespace first int x 5 int y 10 namespace second double x 3 146 double y 2 7183 int main using namespace first cout x endl couri enc cout lt lt second x lt lt endl cout lt lt second y lt lt endl return 0 In this case since we have declared that we were using namespace first all direct uses of x and y without name qualifiers were referring to their declarations in namespace first 121 eplusplus com 2008 All rights reserved 4 The ci Tutorial using and using namespace have validity only in the same block in which they are stated or in the entire code if they are used directly in the global scope For example if we had the intention to first use the objects of one na
86. e flags In addition to eof which checks if the end of file has been reached other member functions exist to check the state of a stream all of them return a bool value bad Returns true if a reading or writing operation fails For example in the case that we try to write to a file that is not open for writing or if the device where we try to write has no space left fail Returns true in the same cases as bad but also in the case that a format error happens like when an alphabetical character is extracted when we are trying to read an integer number eof Returns true if a file open for reading has reached the end good It is the most generic state flag it returns false in the same cases in which calling any of the previous functions would return true In order to reset the state flags checked by any of these member functions we have just seen we can use the member function clear which takes no parameters get and put stream pointers All i o streams objects have at least one internal stream pointer ifstream like istream has a pointer known as the get pointer that points to the element to be read in the next input operation 141 eplusplus com 2008 All rights reserved 4 The enge Tutorial ofstream like ostream has a pointer known as the put pointer that points to the location where the next element has to be written Finally stream inherits both the get and the put pointers fro
87. e for each type In C this can be achieved using template parameters A template parameter is a special kind of parameter that can be used to pass a type as argument just like regular function parameters can be used to pass values to a function template parameters allow to pass also types to a function These function templates can use these parameters as if they were any other regular type The format for declaring function templates with type parameters is template class identifier function declaration template typename identifier function declaration The only difference between both prototypes is the use of either the keyword class or the keyword typename Its use is indistinct since both expressions have exactly the same meaning and behave exactly the same way For example to create a template function that returns the greater one of two objects we could use template class myType gt myType GetMax myType a myType b return a gt b a b Here we have created a template function with myType as its template parameter This template parameter represents a type that has not yet been specified but that can be used in the template function as if it were a regular type As you can see the function template GetMax returns the greater of two parameters of this still undefined type To use this function template we use the following format for the function call function name type parameters For example t
88. e operand located at its right and the only thing that it does is to inverse the value of it producing false if its operand is true and true if its operand is false Basically it returns the opposite Boolean value of evaluating its operand For example 1 5 5 evaluates to false because the expression at its right 5 5 is true u 4 evaluates to true because 6 4 would be false true evaluates to false false evaluates to true The logical operators amp amp and are used when evaluating two expressions to obtain a single relational result The operator amp amp corresponds with Boolean logical operation AND This operation results true if both its two operands are true and false otherwise The following panel shows the result of operator amp amp evaluating the expression a amp amp b amp amp OPERATOR a b a amp amp b true true true true falseffalse falsejtrue false falsefalsefalse The operator corresponds with Boolean logical operation OR This operation results true if either one of its two operands is true thus being false only when both operands are false themselves Here are the possible results of a b 24 eplusplus com 2008 All rights reserved 4 The Crt ig n Tutorial OPERATOR a b ja b true true true true falsetrue falsetrue true falsefalsefalse For example oo amp amp
89. e other without any line break between them This is a sentence This is another sentence even though we had written them in two different insertions into cout In order to perform a line break on the output we must explicitly insert a new line character into cout In C a new line character can be specified as n backslash n cout lt lt First sentence n cout lt lt Second sentence nThird sentence This produces the following output First sentence Second sentence Third sentence Additionally to add a new line you may also use the endl manipulator For example cout First sentence endl cout Second sentence endl would print out First sentence Second sentence The endl manipulator produces a newline character exactly as the insertion of n does but it also has an additional behavior when it is used with buffered streams the buffer is flushed Anyway cout will be an unbuffered stream in most cases so you can generally use both the n escape character and the endl manipulator in order to specify a new line without any difference in its behavior Standard Input cin The standard input device is usually the keyboard Handling the standard input in C is done by applying the overloaded operator of extraction gt gt on the cin stream The operator must be followed by the variable that will store the data that is going to be extracted from the stream For example int ag
90. e passed to the function were copies of their values but never the variables themselves For example suppose that we called our first function addition using the following code Int FS Wes Z z addition x y What we did in this case was to call to function addition passing the values of x and y i e 5 and 3 respectively but not the variables x and y themselves int addition ant a int bh t 1 z addition 5 3 This way when the function addition is called the value of its local variables a and b become 5 and 3 respectively but any modification to either a or b within the function addition will not have any effect in the values of x and y outside it because variables x and y were not themselves passed to the function but only copies of their values at the moment the function was called But there might be some cases where you need to manipulate from inside a function the value of an external variable For that purpose we can use arguments passed by reference as in the function duplicate of the following example passing parameters by reference x include iostream using namespace std 2 y 6 z 14 void duplicate int amp a int amp b int amp c a 2 b 2 c 2 int main int x 1 y 3 z 7 duplicaten xn We TAE robe M lt lt lt oe Ee WE ES WY KK SN SK return 07 The first thing that should call your attention is that in the declaration of auplicate the type of each paramete
91. e previous example this was myfile and any input or output operation performed on this stream object will be applied to the physical file associated to it In order to open a file with a stream object we use its member function open open filename mode Where filename is a null terminated character sequence of type const char the same type that string literals have representing the name of the file to be opened and mode is an optional parameter with a combination of the following flags 138 eplusplus com 2008 All rights reserved 4 The ci Tutorial ios in Open for input operations ios out Open for output operations ios binary Open in binary mode Set the initial position at the end of the file Ieee rate If this flag is not set to any value the initial position is the beginning of the file ios tapp All output operations are performed at the end of the file appending the content to the current content of the file This flag can only be used in streams open for output only operations in ists If the file opened for output operations already existed before its previous content is deleted and replaced by the new one All these flags can be combined using the bitwise operator OR For example if we want to open the file example bin in binary mode to add data we could do it by the following call to member function open ofstream myfile myfile open examp
92. ects of that type T result Therefore result will be an object of the same type as the parameters a and b when the function template is instantiated with a specific type In this specific case where the generic type T is used as a parameter for GetMax the compiler can find out automatically which data type has to instantiate without having to explicitly specify it within angle brackets like we have done before specifying int and 1ong So we could have written instead aige aby gg GetMax i j Since both i and j are of type int and the compiler can automatically find out that the template parameter can only be int This implicit method produces exactly the same result 114 eplusplus com 2008 All rights reserved 4 The ci Tutorial function template II 6 include lt iostream gt 10 using namespace std template lt class T gt T GetMax T a T b return a gt b a b int main int i 5 j 6 k long 1 10 m 5 n k GetMax i j n GetMax l m cout k endl cout lt lt n lt lt endl return 0 Notice how in this case we called our function template GetMax without explicitly specifying the type between angle brackets The compiler automatically determines what type is needed on each call Because our template function includes only one template parameter class T and the function template itself accepts two parameters both of this T type we cannot call
93. ecuted we must group them in a block by enclosing them in braces Iteration structures loops Loops have as purpose to repeat a statement a certain number of times or while a condition is fulfilled The while loop Its format is while expression statement and its functionality is simply to repeat statement while the condition set in expression is true For example we are going to make a program to countdown using a while loop custom countdown using while Enter the starting number 8 Be Tr Gp S Be Sp 25 Xo musa include lt iostream gt using namespace std int main Bites cout Enter the starting number alin SS mp while n 0 cout lt lt n lt lt ccm cloic lt lt lt Wigineaal Wail a return 0 When the program starts the user is prompted to insert a starting number for the countdown Then the while loop begins if the value entered by the user fulfills the condition n 0 that n is greater than zero the block that follows the condition will be executed and repeated while the condition n 0 remains being true The whole process of the previous program can be interpreted according to the following script beginning in main 35 eplusplus com 2008 All rights reserved 4 The ci Tutorial 1 User assigns a value to n The while condition is checked n 0 At this point there are two posibilities condition is true statement is executed to
94. ee we have declared three arrays of char elements The first two were initialized with string literal constants while the third one was left uninitialized In any case we have to speficify the size of the array in the first two question and greeting the size was implicitly defined by the length of the literal constant they were initialized to While for yourname we have explicitly specified that it has a size of 80 chars Finally sequences of characters stored in char arrays can easily be converted into string objects just by using the assignment operator string mystring char myntcs some text mystring myntcs 62 eplusplus com 2008 All rights reserved 4 The ci Tutorial Pointers We have already seen how variables are seen as memory cells that can be accessed using their identifiers This way we did not have to care about the physical location of our data within memory we simply used its identifier whenever we wanted to refer to our variable The memory of your computer can be imagined as a succession of memory cells each one of the minimal size that computers manage one byte These single byte memory cells are numbered in a consecutive way so as within any block of memory every cell has the same number as the previous one plus one This way each cell can be easily located in the memory because it has a unique address and all the memory cells follow a successive pattern For example if we are look
95. elements and in the list of initial values within braces we have specified 5 values one for each element When an initialization of values is provided for an array C allows the possibility of leaving the square brackets empty 1 In this case the compiler will assume a size for the array that matches the number of values included between braces int billy 1 16 2 77 40 12071 After this declaration array billy would be 5 ints long since we have provided 5 initialization values Accessing the values of an array In any point of a program in which an array is visible we can access the value of any of its elements individually as if it was a normal variable thus being able to both read and modify its value The format is as simple as name index Following the previous examples in which billy had 5 elements and each of those elements was of type int the name which we can use to refer to each element is the following billy 0 billy l billy z billy 3 billy 4 ev 1 I T T For example to store the value 75 in the third element of billy we could write the following statement Igdibdbw 2 5g and for example to pass the value of the third element of billy to a variable called a we could write a loulilily 2 5 Therefore the expression billy 2 is for all purposes like a variable of type int Notice that the third element of billy is specified billy 2 since the first one is billy 0 the second
96. eoe se NE ae ah qae a eadein ec wee edo NU ecce ete 107 Advanced Concepts ossai nuren aan SENAERA EEE EAEEREN EREE 113 ESIISENINNE I S t EE e EEE Eaa NEE EEEE EE Ee EEEE aE Ee SEEDERS 113 NAMES PACES ineens E EE E E dines EA E E EEE 120 EXCEPTIONS A EE OAA E ETE E TE A ET E SA E P AE A TE TEE 123 TYPO CASti M T 127 3 eplusplus com 2008 All rights reserved ji 4 The enge Tutorial Preprocessor directives edet fede de cedent cocta side aeee ee ved ixea uoc ue de gae diesen dene do dede CT nets 133 CHF Standard Library cise ieertve enr Evi ayuu d ena Yu Eo ER YER eo VER YKER KEEN VERE Ve TA Vu E VER YES VE YE EE EY Y EE Ve VY Ee ver TERME TNR 138 Input Output with fil amp s 5 3 cte reete to a abe oer dete Sb eei RE ERR ER RE aan tes 138 4 eplusplus com 2008 All rights reserved 4 The enge Tutorial Introduction Instructions for use To whom is this tutorial directed This tutorial is for those people who want to learn programming in C and do not necessarily have any previous knowledge of other programming languages Of course any knowledge of other programming languages or any general computer skill can be useful to better understand this tutorial although it is not essential It is also suitable for those who need a little update on the new features the language has acquired from the latest standards If you are familiar with the C language you can take the first 3 par
97. eption handlers are declared with the keyword catch which must be placed immediately after the try block exceptions An exception occurred Exception Nr 20 include lt iostream gt using namespace std Eire rn asm y Hf EEY throw 20 catch int e cout lt lt An exception occurred cout lt lt Exception Nr lt lt e lt lt endl return 0 The code under exception handling is enclosed in a try block In this example this code simply throws an exception throw 20 A throw expression accepts one parameter in this case the integer value 20 which is passed as an argument to the exception handler The exception handler is declared with the catch keyword As you can see it follows immediately the closing brace of the try block The catch format is similar to a regular function that always has at least one parameter The type of this parameter is very important since the type of the argument passed by the throw expression is checked against it and only in the case they match the exception is caught We can chain multiple handlers catch expressions each one with a different parameter type Only the handler that matches its type with the argument specified in the throw statement is executed If we use an ellipsis as the parameter of catch that handler will catch any exception no matter what the type of the throw exception is This can be used as a default handler that catches all exceptions not c
98. er 2bytes unsigned 0 to 65535 signed 2147483648 to int Integer 4bytes 2147483647 unsigned 0 to 4294967295 signed 2147483648 to long int long Long integer 4bytes 2147483647 unsigned 0 to 4294967295 Boolean value It can take one of two values true bool or false 1byte true or false float Floating point number 4bytes 3 4e 38 7 digits double Double precision floating point number 8bytes t 1 7e 308 15 digits long double Long double precision floating point number 8bytes 1 7e 308 15 digits wchar t Wide character BET 1 wide character bytes The values of the columns Size and Range depend on the system the program is compiled for The values shown above are those found on most 32 bit systems But for other systems the general specification is that int has the natural size suggested by the system architecture one word and the four integer types char short int and long must each one be at least as large as the one preceding it with char being always 1 byte in size The same applies to the floating point types float double and long double where each one must provide at least as much precision as the preceding one Declaration of variables In order to use a variable in C we must first declare it specifying which data type we want it to be The syntax to declare a new variable is to write the specifier of the desired data type like int bool float followe
99. erhead in running time The format for its declaration is inline type name arguments instructions and the call is just like the call to any other function You do not have to include the iniine keyword when calling the function only in its declaration 50 eplusplus com 2008 All rights reserved 4 The enge Tutorial Most compilers already optimize code to generate inline functions when it is more convenient This specifier only indicates the compiler that inline is preferred for this function Recursivity Recursivity is the property that functions have to be called by themselves It is useful for many tasks like sorting or calculate the factorial of numbers For example to obtain the factorial of a number n the mathematical formula would be n n n 1 n 2 n 3 1 more concretely 5 factorial of 5 would be bb edgp w 4 c c 1 e 120 and a recursive function to calculate this in C could be factorial calculator Please type a number 9 include lt iostream gt 9 362880 using namespace std long factorial long a aise Sl return 4a factorial a 1 else return 1 int main long number cout lt lt Please type a number cin gt gt number cout lt lt number lt lt lt lt factorial number return 0 Notice how in function factorial we included a call to itself but only if the argument passed was greater than 1
100. erived d CDerived pd pb pd dynamic cast CBase amp d ok derived to base dynamic cast CDerived amp b wrong base to derived The second conversion in this piece of code would produce a compilation error since base to derived conversions are not allowed with dynamic cast unless the base class is polymorphic When a class is polymorphic dynamic cast performs a special checking during runtime to ensure that the expression yields a valid complete object of the requested class dynamic cast Null pointer on second type include lt iostream gt cast include lt exception gt using namespace std class CBase virtual void dummy class CDerived public CBase int a int main ery CBase pba new CDerived CBase pbb new CBase CDerived pd pd dynamic cast CDerived pba if pd 0 cout lt lt Null pointer on first type casti lt lt endl pd dynamic cast lt CDerived gt pbb if pd 0 cout lt lt Null pointer on second type cast lt lt endl catch exception amp e cout lt lt Exception lt lt e what return 0 Compatibility note dynamic cast requires the Run Time Type Information RTTI to keep track of dynamic types Some compilers support this feature as an option which is disabled by default This must be enabled for runtime type checking using dynamic cast to work properly The code tries to perform two dynamic casts from pointer o
101. ers p 10 ptt p 20 p amp numbers 2 p 30 p numbers 3 p 40 p numbers pt4 50 for int n 07 ness cout lt lt mimbers n lt lt 1 wp return 0 In the chapter about arrays we used brackets 1 several times in order to specify the index of an element of the array to which we wanted to refer Well these bracket sign operators are also a dereference operator known as offset operator They dereference the variable they follow just as does but they also add the number between brackets to the address being dereferenced For example alli Of H a OEES Stok IN 0 XX amb pointed by a 5 0 These two expressions are equivalent and valid both if a is a pointer or if a is an array Pointer initialization When declaring pointers we may want to explicitly specify which variable we want them to point to int number int tommy amp number The behavior of this code is equivalent to int number int tommy tommy amp number When a pointer initialization takes place we are always assigning the reference value to where the pointer points tommy never the value being pointed tommy You must consider that at the moment of declaring a pointer the asterisk indicates only that it is a pointer it is not the dereference operator although both use the same sign Remember they are two different functions of one sign Thus we must take care not to confuse the previous code with
102. ete example 105 eplusplus com 2008 All rights reserved m o The enge Tutorial multiple inheritance 20 include lt iostream gt 10 using namespace std class CPolygon protected int width height public VOLS eta value samt vais selmits B width a height b E class COutput publie VOLO output int X Ur oro COutput output int 1 f cout i endl class CRectangle public CPolygon public COutput public int area return width height hi class CTriangle public CPolygon public COutput publie int area return width height 2 hi int main CRectangle rect CTriangle trgl rect set values 4 5 trgl set values 4 5 rect output rect area trgl output trgl area return 0 106 eplusplus com 2008 All rights reserved 4 The Crt Lageugee Tutorial Polymorphism Before getting into this section it is recommended that you have a proper understanding of pointers and class Statement Explained in int a b c Classes a gt b Data Structures class a public b Friendship and inheritance Pointers to base class inheritance If any of the following statements seem strange to you you should review the indicated sections One of the key features of derived classes is that a pointer to a derived class is type compatible with a pointer to its base class Polymorphism is the art of ta
103. etle int year struct friends t i string name string email movies t favorite movie charlie maria imn ends Eir endesi eearri After the previous declaration we could use any of the following expressions charlie name maria favorite movie title charlie favorite movie year pfriends gt favorite movie year where by the way the last two expressions refer to the same member 81 eplusplus com 2008 All rights reserved 4 The enge Tutorial Other Data Types Defined data types typedef C allows the definition of our own types based on other existing data types We can do this using the keyword typedef whose format is typedef existing type new type name where existing type is a C fundamental or compound type and new type name is the name for the new type we are defining For example typedef char C typedef unsigned int WORD typedef char pChar typedef char field 50 In this case we have defined four data types C WORD pChar and field as char unsigned int char and char 50 respectively that we could perfectly use in declarations later as any other valid type Cimychan anothercehar rtscli WORD myword pehar Tell p field name typedef does not create different types It only creates synonyms of existing types That means that the type of myword can be considered to be either WORD Or unsigned int since both are in fact the same type typedef can be useful to define a
104. example above this means that if another function existed in addition to main the local variables declared in main could not be accessed from the other function and vice versa Initialization of variables When declaring a regular local variable its value is by default undetermined But you may want a variable to store a concrete value at the same moment that it is declared In order to do that you can initialize the variable There are two ways to do this in C The first one known as c like is done by appending an equal sign followed by the value to which the variable will be initialized type identifier initial value For example if we want to declare an int variable called a initialized with a value of 0 at the moment in which it is declared we could write int a 0 The other way to initialize variables known as constructor initialization is done by enclosing the initial value between parentheses type identifier initial value For example ine s A075 Both ways of initializing variables are valid and equivalent in C initialization of variables 6 include lt iostream gt using namespace std nimimm amem int a 5 initial value 5 int b 2 initial value 2 int result initial value undetermined aca tra result a b couts esit return 0 Introduction to strings Variables that can store non numerical values that are longer than one single character are known a
105. g namespace std void printmessage uU t TM mile msn o Im le int main printmessage return 0 void can also be used in the function s parameter list to explicitly specify that we want the function to take no actual parameters when it is called For example function printmessage could have been declared as void printmessage void cout lt lt Warp ey EUNCETOM e Although it is optional to specify void in the parameter list In C a parameter list can simply be left blank if we want a function with no parameters 45 eplusplus com 2008 All rights reserved 4 The enge Tutorial What you must always remember is that the format for calling a function includes specifying its name and enclosing its parameters between parentheses The non existence of parameters does not exempt us from the obligation to write the parentheses For that reason the call to printmessage is printmessage The parentheses clearly indicate that this is a call to a function and not the name of a variable or some other C statement The following call would have been incorrect printmessage 46 eplusplus com 2008 All rights reserved 4 The Bs Tutorial Functions II Arguments passed by value and by reference Until now in all the functions we have seen the arguments passed to the functions have been passed by value This means that when calling a function with parameters what we hav
106. he fourth result is Eccc return 0 In this case we have created a function called subtraction The only thing that this function does is to subtract both passed parameters and to return the result Nevertheless if we examine function main we will see that we have made several calls to function subtraction We have used some different calling methods so that you see other ways or moments when a function can be called In order to fully understand these examples you must consider once again that a call to a function could be replaced by the value that the function call itself is going to return For example the first case that you should already know because it is the same pattern that we have used in previous examples z subtraction 7 2 Cowie lt lt lt Vas rirse result ae X K lt vag If we replace the function call by the value it returns i e 5 we would have 2 5 cout lt lt Uhe irst result ale W lt lt z As well as cout elhesseconderesulteu seu ccesultEacisioneg 2 has the same result as the previous call but in this case we made the call to subtraction directly as an insertion parameter for cout Simply consider that the result is the same as if we had written cout lt lt Ihe second result is lt lt 5r since 5 is the value returned by subtraction 7 2 In the case of couci lt lt anis celsalaaol iseilic as 9 cS SUDE rac oy E 44 eplusplus com 2008 All rights reserved
107. he syntax of the switch statement is a bit peculiar Its objective is to check several possible constant values for an expression Something similar to what we did at the beginning of this section with the concatenation of several if and else if instructions Its form is the following switch expression case constanti group of statements 1 break case constant2 group of statements 2 break default default group of statements It works in the following way switch evaluates expression and checks if it is equivalent to constant1 if it is it executes group of statements 1 until it finds the break statement When it finds this break statement the program jumps to the end of the switch selective structure If expression was not equal to constant1 it will be checked against constant2 If it is equal to this it will execute group of statements 2 until a break keyword is found and then will jump to the end of the switch selective structure Finally if the value of expression did not match any of the previously specified constants you can include as many case labels as values you want to check the program will execute the statements included after the default label if it exists since it is optional 39 eplusplus com 2008 All rights reserved 4 The ci Tutorial Both of the following code fragments have the same behavior switch example if else equivalent switch x if x 1 eee as cout l
108. her array SO we are not able to copy blocks of data with an assignment operation Assuming mystext is a char variable expressions within a source code like mystext Hello mystext Hello would not be valid like neither would be mystext ur e t Hige URBE you EN On hp The reason for this may become more comprehensible once you know a bit more about pointers since then it will be clarified that an array is in fact a constant pointer pointing to a block of memory Using null terminated sequences of characters Null terminated sequences of characters are the natural way of treating strings in C so they can be used as such in many procedures In fact regular string literals have this type char and can also be used in most cases For example cin and cout support null terminated sequences as valid containers for sequences of characters so they can be used directly to extract strings of characters from cin or to insert them into cout For example 61 eplusplus com 2008 All rights reserved 4 The enge Tutorial null terminated sequences of characters Please enter your first name John include lt iostream gt Hello John using namespace std nt mein 0 char question Please enter your first names o char greeting Hello char yourname 80 cout lt lt question cin yourname cout lt lt greeting lt lt yourname lt lt I return 0 As you can s
109. iables x and y which are private members of class CRectangle which means they are only accessible from other members of their class The only difference between defining a class member function completely within its class or to include only the prototype and later its definition is that in the first case the function will automatically be considered an inline member function by the compiler while in the second it will be a normal not inline class member function which in fact supposes no difference in behavior Members x and y have private access remember that if nothing else is said all members of a class defined with keyword class have private access By declaring them private we deny access to them from anywhere outside the 87 eplusplus com 2008 All rights reserved 4 The Be Tutorial class This makes sense since we have already defined a member function to set values for those members within the object the member function set_values Therefore the rest of the program does not need to have direct access to them Perhaps in a so simple example as this it is difficult to see an utility in protecting those two variables but in greater projects it may be very important that values cannot be modified in an unexpected way unexpected from the point of view of the object One of the greater advantages of a class is that as any other type we can declare several objects of it For example following with the previous
110. icult or impossible to express otherwise in the source code of a program like newline Xn or tab c All of them are preceded by a backslash Here you have a list of some of such escape codes 18 eplusplus com 2008 All rights reserved 4 The iz Tutorial njnewline Mr carriage return NC tab W vertical tab 4 b backspace flform feed page feed Na alert beep V single quote w V double quote NV question mark Ny backslash For example Naa Nea hByeas We RIGHI one ntwo nthree Additionally you can express any character by its numerical ASCII code by writing a backslash character followed by the ASCII code expressed as an octal base 8 or hexadecimal base 16 number In the first case octal the digits must immediately follow the backslash for example 23 or 40 in the second case hexadecimal an x character must be written before the digits themselves for example x20 or x4A String literals can extend to more than a single line of code by putting a backslash sign at the end of each unfinished line String expressed in two lines You can also concatenate several string constants separating them by one or several blank spaces tabulators newline or any other valid blank character Seni S omms Wa smile strom otiam acte s Finally if we want the string literal to be explicitly made of wide characters wchar t
111. id printmovie movies t movie cout movie title Come lt lt W UU lt lt movie yec lt lt Un WE Pointers to structures Blade Runner 982 Matriz 999 Taxi Driver Spa red these movies 1982 ILS Like any other type structures can be pointed by its own type of pointers struct movies t Stering TELE p int year H movies t amovie movies t pmovie Here amovie is an object of structure type movies t and pmovie is a pointer to point to objects of structure type movies t So the following code would also be valid pmovie amp amovie The value of the pointer pmovie would be assigned to a reference to the object amovie its memory address 79 eplusplus com 2008 All rights reserved 4 The enge Tutorial We will now go with another example that includes pointers which will serve to introduce a new operator the arrow operator pointers to structures Enter title Invasion of the body snatchers include lt iostream gt Enter year 1978 include lt string gt include lt sstream gt You have entered using namespace std Invasion of the body snatchers 1978 Stree moviese te string title int year int main string mystr movies t amovie movies t pmovie pmovie amp amovie cout Enter title getline cin pmovie gt title cout lt lt Enter year getline cin mystr stringstream mystr gt gt pmo
112. iduously in other sections of this tutorial When the preprocessor finds an include directive it replaces it by the entire content of the specified file There are two ways to specify a file to be included include file include lt file gt The only difference between both expressions is the places directories where the compiler is going to look for the file In the first case where the file name is specified between double quotes the file is searched first in the same directory that includes the file containing the directive In case that it is not there the compiler searches the file in the default directories where it is configured to look for the standard header files If the file name is enclosed between angle brackets lt gt the file is searched directly where the compiler is configured to look for the standard header files Therefore standard header files are usually included in angle brackets while other specific header files are included using quotes Pragma directive pragma This directive is used to specify diverse options to the compiler These options are specific for the platform and the compiler you use Consult the manual or the reference of your compiler for more information on the possible parameters that you can define with pragma If the compiler does not support a specific argument for pragma it is ignored no error is generated Predefined macro names The following macro names are defined at any time
113. if something else than the variable declarations themselves looks a bit strange to you You will see the rest in detail in coming sections Scope of variables All the variables that we intend to use in a program must have been declared with its type specifier in an earlier point in the code like we did in the previous code at the beginning of the body of the function main when we declared that a b and result were of type int A variable can be either of global or local scope A global variable is a variable declared in the main body of the source code outside all functions while a local variable is one declared within the body of a function or a block include lt iostream using namespace std int Integer char aCharacter char string 70 unsigned int Humber0f Sons Global variables int main i unsigned short Age float AHumber Another ne Local variahles cout lt lt Enter your age cin gt Age Instructions Global variables can be referred from anywhere in the code even inside functions whenever it is after its declaration 14 eplusplus com 2008 All rights reserved 4 The iy Tutorial The scope of local variables is limited to the block enclosed in braces where they are declared For example if they are declared at the beginning of the body of a function like in function main their scope is between its declaration point and the end of that function In the
114. igns to it a reference to an object of another incompatible type using explicit type casting padd CAddition amp d Traditional explicit type casting allows to convert any pointer into any other pointer type independently of the types they point to The subsequent call to member result will produce either a run time error or a unexpected result In order to control these types of conversions between classes we have four specific casting operators dynamic cast reinterpret cast static cast and const cast Their format is to follow the new type enclosed between angle brackets and immediately after the expression to be converted between parentheses dynamic cast new type expression reinterpret cast new type expression Static cast new type expression const cast new type expression The traditional type casting equivalents to these expressions would be new type expression new type expression but each one with its own special characteristics dynamic cast dynamic cast can be used only with pointers and references to objects Its purpose is to ensure that the result of the type conversion is a valid complete object of the requested class Therefore dynamic cast is always successful when we cast a class to one of its base classes 128 eplusplus com 2008 All rights reserved 4 The enge Tutorial class CBase class CDerived public CBase CBase b CBase pb CD
115. ing for cell 1776 we know that it is going to be right between cells 1775 and 1777 exactly one thousand cells after 776 and exactly one thousand cells before cell 2776 Reference operator amp As soon as we declare a variable the amount of memory needed is assigned for it at a specific location in memory its memory address We generally do not actively decide the exact location of the variable within the panel of cells that we have imagined the memory to be Fortunately that is a task automatically performed by the operating system during runtime However in some cases we may be interested in knowing the address where our variable is being stored during runtime in order to operate with relative positions to it The address that locates a variable within memory is what we call a reference to that variable This reference to a variable can be obtained by preceding the identifier of a variable with an ampersand sign amp known as reference operator and which can be literally translated as address of For example ted amp andy This would assign to ted the address of variable andy since when preceding the name of the variable andy with the reference operator amp we are no longer talking about the content of the variable itself but about its reference i e its address in memory From now on we are going to assume that andy is placed during runtime in the memory address 1776 This number 1776 is just an arbitrary assumption
116. int n result 0 int main oie 3e f toss 6 iar J result billy n cout lt lt result return 0 Multidimensional arrays Multidimensional arrays can be described as arrays of arrays For example a bidimensional array can be imagined as a bidimensional table made of elements all of them of a same uniform data type 1 2 3 4 jimmy jimmy represents a bidimensional array of 3 per 5 elements of type int The way to declare this array in C would be ime Jane ES LSP and for example the way to reference the second element vertically and fourth horizontally in an expression would be jimmy 1 3 56 cplusplus com 2008 All rights reserved 4 The iz Tutorial jimmy jimmy 1 3 remember that array indices always begin by zero Multidimensional arrays are not limited to two indices i e two dimensions They can contain as many indices as needed But be careful The amount of memory needed for an array rapidly increases with each dimension For example char century 100 365 24 60 60 declares an array with a char element for each second in a century that is more than 3 billion chars So this declaration would consume more than 3 gigabytes of memory Multidimensional arrays are just an abstraction for programmers since we can obtain the same results with a simple array just by putting a factor between its indices aioe amy ES LS e is equ
117. int number int tommy tommy amp number that is incorrect and anyway would not have much sense in this case if you think about it As in the case of arrays the compiler allows the special case that we want to initialize the content at which the pointer points with constants at the same moment the pointer is declared char terry hello 68 eplusplus com 2008 All rights reserved 4 The cr e Tutorial In this case memory space is reserved to contain hello and then a pointer to the first character of this memory block is assigned to terry If we imagine that hello is stored at the memory locations that start at addresses 1702 we can represent the previous declaration as 1702 1703 1704 1705 1706 1707 terry 1702 It is important to indicate that terry contains the value 1702 and not h nor hello although 1702 indeed is the address of both of these The pointer terry points to a sequence of characters and can be read as if it was an array remember that an array is just like a constant pointer For example we can access the fifth element of the array with any of these two expression terryt4 terry 4 Both expressions have a value of o the fifth element of the array Pointer arithmetics To conduct arithmetical operations on pointers is a little different than to conduct them on regular integer data types To begin with only addition and subtraction operations are allowed to b
118. is as simple as dime biliy Wee NOTE The elements field within brackets which represents the number of elements the array is going to hold must be a constant value since arrays are blocks of non dynamic memory whose size must be determined before execution In order to create arrays with a variable length dynamic memory is needed which is explained later in these tutorials Initializing arrays When declaring a regular array of local scope within a function for example if we do not specify otherwise its elements will not be initialized to any value by default so their content will be undetermined until we store some value in them The elements of global and static arrays on the other hand are automatically initialized with their default values which for all fundamental types this means they are filled with zeros In both cases local and global when we declare an array we have the possibility to assign initial values to each one of its elements by enclosing the values in braces For example sene odiy tal S 4 lep 27 Wp do 207i wg This declaration would have created an array like this 54 cplusplus com 2008 All rights reserved 4 The ci Tutorial 1 2 3 4 billy el o a o an The amount of values between braces must not be larger than the number of elements that we declare for the array between square brackets For example in the example of array billy we have declared that it has 5
119. ivalent to int jimmy 15 8 5 15 With the only difference that with multidimensional arrays the compiler remembers the depth of each imaginary dimension for us Take as example these two pieces of code with both exactly the same result One uses a bidimensional array and the other one uses a simple array multidimensional array pseudo multidimensional array define WIDTH 5 define WIDTH 5 define HEIGHT 3 define HEIGHT 3 int jimmy HEIGHT WIDTH int jimmy HEIGHT WIDTH int n m int n m int main int main for n 0 n lt HEIGHT n for n 0 n lt HEIGHT n for m 0 m lt WIDTH m for m 0 m lt WIDTH m jimmy n m n 1 m 1 jimmy n WIDTH m n 1 m 1 return 0 return 0 None of the two source codes above produce any output on the screen but both assign values to the memory block called jimmy in the following way jimmy 57 eplusplus com 2008 All rights reserved 4 The ig n Tutorial We have used defined constants define to simplify possible future modifications of the program For example in case that we decided to enlarge the array to a height of 4 instead of 3 it could be done simply by changing the line define HEIGHT 3 to define HEIGHT 4 with no need to make any other modifications to the program Arrays as parameters At some moment we may need to pass an array to a function as a parameter In C it is not possible to pa
120. izes function addition and returns the control back to the function that called it in the first place in this case main At this moment the program follows it regular course from the same point at which it was interrupted by the call to addition But additionally because the return statement in function addition specified a value the content of variable r return r which at that moment had a value of 8 This value becomes the value of evaluating the function call int addition int a int bh p z addition 5 3 4 So being the value returned by a function the value given to the function call itself when it is evaluated the variable z will be set to the value returned by addition 5 3 that is 8 To explain it another way you can imagine that the call to a function addition 5 3 is literally replaced by the value it returns 8 The following line of code in main is cout lt lt The result is lt lt zr That as you may already expect produces the printing of the result on the screen 42 eplusplus com 2008 All rights reserved 4 The cH agure Tutorial Scope of variables The scope of variables declared within a function or any other inner block is only their own function or their own block and cannot be used outside of them For example in the previous example it would have been impossible to use the variables a b or r directly in function main since they were variables local to function a
121. king advantage of this simple but powerful and versatile feature that brings Object Oriented Methodologies to its full potential We are going to start by rewriting our program about the rectangle and the triangle of the previous section taking into consideration this pointer compatibility property pointers to base class 20 include lt iostream gt 10 using namespace std class CPolygon i protected int width height pubic void set_values int a int b width a height b class CRectangle public CPolygon pupie int area return width height hi class CTriangle public CPolygon jelblouk skiers int area return width height 2 hi int main CRectangle rect CTriangle trol CPolygon ppolyl amp rect CPolygon ppoly2 amp trgl ppolyl set values 4 5 ppoly2 set values 4 5 cout rect area endl cout trgl area endl return 0 In function main we create two pointers that point to objects of class CPolygon ppoly1 and ppoly2 Then we assign references to rect and trgl1 to these pointers and because both are objects of classes derived from CPolygon both are valid assignment operations The only limitation in using ppoly1 and ppoly2 instead of rect and trg1 is that both ppoly1 and ppoly2 are of type CPolygon and therefore we can only use these pointers to refer to the members that CRectangle and 107 eplusplus com 2008 A
122. lass includes a default constructor and a copy constructor even if they are not declared it also includes a default definition for the assignment operator with the class itself as parameter The behavior which is defined by default is to copy the whole content of the data members of the object passed as argument the one at the right side of the sign to the one at the left side pvectorec 2 9 CVector e e d copy assignment operator The copy assignment operator function is the only operator member function implemented by default Of course you can redefine it to any other functionality that you want like for example copy only certain class members or perform additional initialization procedures The overload of operators does not force its operation to bear a relation to the mathematical or usual meaning of the operator although it is recommended For example the code may not be very intuitive if you use operator to subtract two classes or operator to fill with zeros a class although it is perfectly possible to do so Although the prototype of a function operator can seem obvious since it takes what is at the right side of the operator as the parameter for the operator member function of the object at its left side other operators may not be so obvious Here you have a table with a summary on how the different operator functions have to be declared replace by the operator in each case Expression Operator Membe
123. lasses We simply have to consider that once declared a class becomes a valid type so we can use the class name as the type for the pointer For example CRectangle prect is a pointer to an object of class CRectangle As it happened with data structures in order to refer directly to a member of an object pointed by a pointer we can use the arrow operator of indirection Here is an example with some possible combinations 92 eplusplus com 2008 All rights reserved 4 The cr e Tutorial pointer to classes example a area 2 include lt iostream gt joy area 12 using namespace std c area 2 d 0 area 30 class CRectangle GI area 56 int width height puple void set values ant m int area void return width height vordi Rectangle seti values Ontan mter width a height b int main CRectangle ar b 4e CRectangle d new CRectangle 2 b new CRectangle c amp a eoGee wales l 2 7 b set values 3 4 d set values 5 6 d T set values 7 8 cout a area a area endl cout b area b area endl cout c area c area endl cout lt lt d 0 area lt lt d O0 area lt lt endl cout lt lt ad 1 area lt lt d l area lt lt endl delete d delete b return 0 Next you have a summary on how can you read some pointer and class operators amp gt
124. le bin ios out ios app ios binary Each one of the open member functions of the classes ofstream ifstream and fstream has a default mode that is used if the file is opened without a second argument class default mode parameter ofstreamiios out ifstream ios in fstream jios in ios out For ifstream and ofstream Classes ios in and ios out are automatically and respectively assumed even if a mode that does not include them is passed as second argument to the open member function The default value is only applied if the function is called without specifying any value for the mode parameter If the function is called with any value in that parameter the default mode is overridden not combined File streams opened in binary mode perform input and output operations independently of any format considerations Non binary files are known as text files and some translations may occur due to formatting of some special characters like newline and carriage return characters Since the first task that is performed on a file stream object is generally to open a file these three classes include a constructor that automatically calls the open member function and has the exact same parameters as this member Therefore we could also have declared the previous myfile object and conducted the same opening operation in our previous example by writing ofstream myfile example bin ios out ios app ios bina
125. le positioning and is the type returned by file tellg This type is defined as an integer type therefore we can conduct on it the same operations we conduct on any other integer value and can safely be converted to another integer type large enough to contain the size of the file For a file with a size under 2GB we could use int int size Size int file tellg Once we have obtained the size of the file we request the allocation of a memory block large enough to hold the entire file memblock new char size Right after that we proceed to set the get pointer at the beginning of the file remember that we opened the file with this pointer at the end then read the entire file and finally close it file seekg 0 ios beg file read memblock size file close At this point we could operate with the data obtained from the file Our program simply announces that the content of the file is in memory and then terminates Buffers and Synchronization When we operate with file streams these are associated to an internal buffer of type streambuf This buffer is a memory block that acts as an intermediary between the stream and the physical file For example with an ofstream each time the member function put which writes a single character is called the character is not written directly to the physical file with which the stream is associated Instead of that the character is inserted in that stream s intermediate buffer
126. le that overloads the addition operator We are going to create a class to store bidimensional vectors and then we are going to add two of them a 3 1 and p 1 2 The addition of two bidimensional vectors is an operation as simple as adding the two x coordinates to obtain the resulting x coordinate and adding the two y coordinates to obtain the resulting y In this case the result will be 3 1 1 2 4 3 95 eplusplus com 2008 All rights reserved 4 The igege Tutorial vectors overloading operators example 4 3 include lt iostream gt using namespace std class CVector public IHME ESSE CVector greet Entrer enims CVector operator CVector CVector CVector int a int b x a y b CVector CVector operator CVector param CVector temp temp x x param x temp y y param y return temp ine main F d CVector a 3L CVector p b 2e CVector c c a b Cout lt lt Go lt lt T lt lt Cae return 0 It may be a little confusing to see so many times the CVector identifier But consider that some of them refer to the class name type CVector and some others are functions with that name constructors must have the same name as the class Do not confuse them CVector aini imne function name CVector constructor CVector operatorn CVector function returns a CVector The function operator of class CVector is the one that is in charge of overlo
127. led product with two members weight and price each of a different fundamental type We have then used this name of the structure type product to declare three objects of that type apple banana and melon as we would have done with any fundamental data type Once declared product has become a new valid type name like the fundamental ones int char or short and from that point on we are able to declare objects variables of this compound new type like we have done with apple banana and melon Right at the end of the struct declaration and before the ending semicolon we can use the optional field object name to directly declare objects of the structure type For example we can also declare the structure objects apple banana and melon at the moment we define the data structure type this way SEBUCE product di int weight float price apple banana melon It is important to clearly differentiate between what is the structure type name and what is an object variable that has this structure type We can instantiate many objects i e variables like apple banana and melon froma single structure type product 77 cplusplus com 2008 All rights reserved 4 The cr e Tutorial Once we have declared our three objects of a determined structure type apple banana and melon we can operate directly with their members To do that we use a dot inserted between the object name and the member name For example we coul
128. ll rights reserved 4 The cr e Tutorial CTriangle inherit from CPolygon For that reason when we call the area members at the end of the program we have had to use directly the objects rect and trg1 instead of the pointers ppoly1 and ppoly2 In order to use area with the pointers to class CPolygon this member should also have been declared in the class CPolygon and not only in its derived classes but the problem is that CRectangie and CTriangle implement different versions of area therefore we cannot implement it in the base class This is when virtual members become handy Virtual members A member of a class that can be redefined in its derived classes is known as a virtual member In order to declare a member of a class as virtual we must precede its declaration with the keyword virtual virtual members 20 include lt iostream gt 10 using namespace std 0 class CPolygon protected int width height jeollexlbsberg void set values int a int b width a height b virtual int area return 0 class CRectangle public CPolygon jeisllelabreng int area return width height class CTriangle public CPolygon joules int area return width height 2 E int main CRectangle rect CTriangle tral CPolygon poly CPolygon ppolyl amp rect CPolygon ppoly2 stral CPolygon ppoly3 amp poly ppolyl setovaluesc 45y peolly2 gt set values 475
129. llow us to access the same group of 4 bytes mix l mix s and mix c and which we can use according to how we want to access these bytes as if they were a single 1ong type data as if they were two short elements or as an array of char elements respectively I have mixed types arrays and structures in the union so that you can see the different ways that we can access the data For a ittle endian system most PC platforms this union could be represented as mix l mix z hi mix s lo mix c iu mix c 1 mix c mix c 3 The exact alignment and order of the members of a union in memory is platform dependant Therefore be aware of possible portability issues with this type of use Anonymous unions In C we have the option to declare anonymous unions If we declare a union without any name the union will be anonymous and we will be able to access its members directly by their member names For example look at the difference between these two structure declarations 83 eplusplus com 2008 All rights reserved 4 The enge Tutorial structure with regular union structure with anonymous union struct struct 4 char title 50 char title 50 char author 50 char author 50 union union float dollars float dollars int yens int yens price book book The only difference between the two pieces of code is that in the first one we have given a name to the union
130. loop Initialization Condition a Increase n starts with a value of 0 and i with 100 the condition is n i that n is not equal to i Because n is increased by one and i decreased by one the loop s condition will become false after the 50th loop when both n and i will be equal to 50 for 37 eplusplus com 2008 All rights reserved 4 The Bs Tutorial Jump statements The break statement Using break we can leave a loop even if the condition for its end is not fulfilled It can be used to end an infinite loop or to force it to end before its natural end For example we are going to stop the count down before its natural end maybe because of an engine check failure break loop example dO 97 8 le oO 5 4r 5 Cowacdowa acorted include lt iostream gt using namespace std int main aloe dap for n 10 n gt 0 n Come lt lt m KK V We if n 3 cout lt lt countdown aborted break return 0 The continue statement The continue statement causes the program to skip the rest of the loop in the current iteration as if the end of the statement block had been reached causing it to jump to the start of the following iteration For example we are going to skip the number 5 in our countdown continue loop example 10 OG We G 27 3 B Wy aa include lt iostream gt using namespace std int main fom ante n 10 pU EET if n 5 continue Go
131. m iostream which is itself derived from both istream and ostream These internal stream pointers that point to the reading or writing locations within a stream can be manipulated using the following member functions tellg and tellp These two member functions have no parameters and return a value of the member type pos type which is an integer data type representing the current position of the get stream pointer in the case of te11g or the put stream pointer in the case of tellp seekg and seekp These functions allow us to change the position of the get and put stream pointers Both functions are overloaded with two different prototypes The first prototype is seekg position seekp position Using this prototype the stream pointer is changed to the absolute position position counting from the beginning of the file The type for this parameter is the same as the one returned by functions te11g and tellp the member type pos type Which is an integer value The other prototype for these functions is seekg offset direction seekp offset direction Using this prototype the position of the get or put pointer is set to an offset value relative to some specific point determined by the parameter direction offset is of the member type off type which is also an integer type And direction is of type seekdir which is an enumerated type enum that determines the point from where offset is counted from and th
132. mber 0 to end 12345 You entered 12345 include lt iostream gt Enter number 0 to end 160277 using namespace std You entered 160277 Enter number 0 to end 0 Taimani You entered 0 unsigned long n do cout Enter number 0 to end cin SS n cout lt lt You entered lt lt nee Nn while n 0 return 0 The do while loop is usually used when the condition that has to determine the end of the loop is determined within the loop statement itself like in the previous case where the user input within the block is what is used to determine if the loop has to end In fact if you never enter the value 0 in the previous example you can be prompted for more numbers forever The for loop Its format is for initialization condition increase statement 36 eplusplus com 2008 All rights reserved 4 The ci Tutorial and its main function is to repeat statement while condition remains true like the while loop But in addition the for loop provides specific locations to contain an initialization statement and an increase statement So this loop is specially designed to perform a repetitive action with a counter which is initialized and increased on each iteration It works in the following way 1 initialization is executed Generally it is an initial value setting for a counter variable This is executed only once 2 condition is checked If it is true the loop continues
133. mespace and then those of another one we could do something like using namespace example 5 include lt iostream gt 3 1416 using namespace std namespace first ine eo namespace second double x 3 1416 int main using namespace first cout lt lt x lt lt endl using namespace second cout lt lt x lt lt endl return 0 Namespace alias We can declare alternate names for existing namespaces according to the following format namespace new name current name Namespace std All the files in the C standard library declare all of its entities within the std namespace That is why we have generally included the using namespace std statement in all programs that used any entity defined in iostream 122 eplusplus com 2008 All rights reserved 4 The cr e Tutorial Exceptions Exceptions provide a way to react to exceptional circumstances like runtime errors in our program by transferring control to special functions called handlers To catch exceptions we must place a portion of code under exception inspection This is done by enclosing that portion of code in a try block When an exceptional circumstance arises within that block an exception is thrown that transfers the control to the exception handler If no exception is thrown the code continues normally and all handlers are ignored A exception is thrown by using the throw keyword from inside the try block Exc
134. n alias for a type that is frequently used within a program It is also useful to define types when it is possible that we will need to change the type in later versions of our program or if a type you want to use has a name that is too long or confusing Unions Unions allow one same portion of memory to be accessed as different data types since all of them are in fact the same location in memory Its declaration and use is similar to the one of structures but its functionality is totally different union union name member typel member namel member type2 member name2 member type3 member name3 object names All the elements of the union declaration occupy the same physical space in memory Its size is the one of the greatest element of the declaration For example 82 eplusplus com 2008 All rights reserved 4 The enge Tutorial union mytypes t echar e imb xc float mytypes defines three elements mytypes c mytypes i mytypes f each one with a different data type Since all of them are referring to the same location in memory the modification of one of the elements will affect the value of all of them We cannot store different values in them independent of each other One of the uses a union may have is to unite an elementary type with an array or structures of smaller elements For example union mix t Tong ls Struck Shore ne short lo joe cage P mik defines three names that a
135. name where type is the data type of the value that the pointer is intended to point to This type is not the type of the pointer itself but the type of the data the pointer points to For example int number chan character float greatnumber These are three declarations of pointers Each one is intended to point to a different data type but in fact all of them are pointers and all of them will occupy the same amount of space in memory the size in memory of a pointer depends on the platform where the code is going to run Nevertheless the data to which they point to do not occupy the same amount of space nor are of the same type the first one points to an int the second one to a char and the last one to a float Therefore although these three example variables are all of them pointers which occupy the same size in memory they are said to have different types int char and float respectively depending on the type they point to I want to emphasize that the asterisk sign that we use when declaring a pointer only means that it is a pointer it is part of its type compound specifier and should not be confused with the dereference operator that we have seen a bit earlier but which is also written with an asterisk They are simply two different things represented with the same sign 65 cplusplus com 2008 All rights reserved 4 The enge Tutorial Now have a look at this code my first pointer fir
136. ndl delete c cout lt lt CDummy n lt lt endl return 0 In fact static members have the same properties as global variables but they enjoy class scope For that reason and to avoid them to be declared several times we can only include the prototype its declaration in the class declaration but not its definition its initialization In order to initialize a static data member we must include a formal definition outside the class in the global scope as in the previous example int CDummy n 0 Because it is a unique variable value for all the objects of the same class it can be referred to as a member of any object of that class or even directly by the class name of course this is only valid for static members cout lt lt acn COU S C a These two calls included in the previous example are referring to the same variable the static variable n within class CDummy shared by all objects of this class Once again I remind you that in fact it is a global variable The only difference is its name and possible access restrictions outside its class Just as we may include static data within a class we can also include static functions They represent the same they are global functions that are called as if they were object members of a given class They can only refer to static data in no case to non static members of the class as well as they do not allow the use of the keyword this since it makes reference to an object poi
137. ne contained in b is 7 Notice how a was not affected by the final modification of b even though we declared a b earlier that is because of the right to left rule 21 cplusplus com 2008 All rights reserved 4 The ci Tutorial A property that C has over other programming languages is that the assignment operation can be used as the rvalue or part of an rvalue for another assignment operation For example is equivalent to op p that means first assign 5 to variable p and then assign to a the value 2 plus the result of the previous assignment of p i e 5 leaving a with a final value of 7 The following expression is also valid in C It assigns 5 to the all the three variables a b and c Arithmetic operators The five arithmetical operations supported by the C language are addition subtraction multiplication division 9o modulo Operations of addition subtraction multiplication and division literally correspond with their respective mathematical operators The only one that you might not be so used to see is modulo whose operator is the percentage sign s Modulo is the operation that gives the remainder of a division of two values For example if we write a 11 3 3 the variable a will contain the value 2 since 2 is the remainder from dividing 11 between 3 Compound assignment z gt gt lt lt am
138. nted by pl pl p2 pl p2 value of pointer is copied ed Zr value pointed by pl 20 cout cintas ccn stsvallues endi cout secondvalue is secondvalue endl return 0 I have included as a comment on each line how the code can be read ampersand as address of and asterisk as value pointed by Notice that there are expressions with pointers p1 and p2 both with and without dereference operator The meaning of an expression using the dereference operator is very different from one that does not When this operator precedes the pointer name the expression refers to the value being pointed while when a pointer name appears without this operator it refers to the value of the pointer itself i e the address of what the pointer is pointing to 66 eplusplus com 2008 All rights reserved 4 The enge Tutorial Another thing that may call your attention is the line ine jel jee This declares the two pointers used in the previous example But notice that there is an asterisk for each pointer in order for both to have type int pointer to int Otherwise the type for the second variable declared in that line would have been int and not int because of precedence relationships If we had written int pl per p1 would indeed have int type but p2 would have type int spaces do not matter at all for this purpose This is due to operator precedence rules But a
139. nter and these functions in fact are not members of any object but direct members of the class 99 l cplusplus com 2008 All rights reserved 4 The Crt Lageugee Tutorial Friendship and inheritance Friend functions In principle private and protected members of a class cannot be accessed from outside the same class in which they are declared However this rule does not affect friends Friends are functions or classes declared as such If we want to declare an external function as friend of a class thus allowing this function to have access to the private and protected members of this class we do it by declaring a prototype of this external function within the class and preceding it with the keyword friend friend functions 24 include lt iostream gt using namespace std class CRectangle int width height PUBIE vordiiset i valucssi Gnt INE int area return width height friend CRectangle duplicate CRectangle vorde Rectangle seti values Ontika mite width a height b CRectangle duplicate CRectangle rectparam CRectangle rectres rectres width rectparam width 2 rectres height rectparam height 2 return rectres int main CRectangle rect rectb rect set values 2 3 rectb duplicate rect cout rectb area return 0 The duplicate function is a friend of cRectangle From within that function we have been able to access the members width
140. nyway simply remembering that you have to put one asterisk per pointer is enough for most pointer users Pointers and arrays The concept of array is very much bound to the one of pointer In fact the identifier of an array is equivalent to the address of its first element as a pointer is equivalent to the address of the first element that it points to so in fact they are the same concept For example supposing these two declarations int numbers 20 align eg The following assignment operation would be valid p numbers After that p and numbers would be equivalent and would have the same properties The only difference is that we could change the value of pointer p by another one whereas numbers will always point to the first of the 20 elements of type int with which it was defined Therefore unlike p which is an ordinary pointer numbers is an array and an array can be considered a constant pointer Therefore the following allocation would not be valid numbers p Because numbers is an array so it operates as a constant pointer and we cannot assign values to constants Due to the characteristics of variables all expressions that include pointers in the following example are perfectly valid 67 eplusplus com 2008 All rights reserved 4 The enge Tutorial more pointers 10 20 30 40 50 include lt iostream gt using namespace std int main int numbers 5 ant pF p numb
141. o call GetMax to compare two integer values of type int we can write aoe See NVA GetMax int x y When the compiler encounters this call to a template function it uses the template to automatically generate a function replacing each appearance of myType by the type passed as the actual template parameter int in this case and then calls it This process is automatically performed by the compiler and is invisible to the programmer Here is the entire example 113 cplusplus com 2008 All rights reserved 4 The ci Tutorial function template 6 include iostream 10 using namespace std template class T lr GetMax Ta T b T result result a gt b a b return result ipt main TI int i 5 j 6 k long 1 10 m 5 n k GetMax lt int gt i j n GetMax lt long gt l m cout lt lt k lt lt endl cout lt lt m lt lt endl return 0 In this case we have used T as the template parameter name instead of myType because it is shorter and in fact is a very common template parameter name But you can use any identifier you like In the example above we used the function template GetMax twice The first time with arguments of type int and the second one with arguments of type long The compiler has instantiated and then called each time the appropriate version of the function As you can see the type T is used within the GetMax template function even to declare new obj
142. o declare an object of type CPolygon and to call its own area function which always returns 0 Abstract base classes Abstract base classes are something very similar to our CPolygon class of our previous example The only difference is that in our previous example we have defined a valid area function with a minimal functionality for objects that were of class CPolygon like the object poly whereas in an abstract base classes we could leave that area member function without implementation at all This is done by appending 0 equal to zero to the function declaration An abstract base CPolygon class could look like this abstract class CPolygon class CPolygon protected int width height publiek voidiset values Glinie el ane width a height b virtual int area 0 Notice how we appended 0 to virtual int area instead of specifying an implementation for the function This type of function is called a pure virtual function and all classes that contain at least one pure virtual function are abstract base classes The main difference between an abstract base class and a regular polymorphic class is that because in abstract base classes at least one of its members lacks implementation we cannot create instances objects of it But a class that cannot instantiate objects is not totally useless We can create pointers to it and take advantage of all its polymorphic abilities Therefore a declaration like
143. omment discards everything between the characters and the first appearance of the characters with the possibility of including more than one line We are going to add comments to our second program eplusplus com 2008 All rights reserved P The enge Tutorial my second program in Ct with more comments include lt iostream gt using namespace std biome enkon GO tH emo World cout lt lt I m a C program Cr Progra return 0 prints Hello APRINS Gma Hello World I m a C program If you include comments within the source code of your programs without using the comment characters combinations or the compiler will take them as if they were C expressions most likely causing one or several error messages when you compile it 10 eplusplus com 2008 All rights reserved 4 The ci Tutorial Variables Data Types The usefulness of the Hello World programs shown in the previous section is quite questionable We had to write several lines of code compile them and then execute the resulting program just to obtain a simple sentence written on the screen as result It certainly would have been much faster to type the output sentence by ourselves However programming is not limited only to printing simple texts on the screen In order to go a little further on and to become able to write programs that perform useful tasks that really save us w
144. on ifndef serves for the exact opposite the code between ifndef and endif directives is only compiled if the specified identifier has not been previously defined For example 134 eplusplus com 2008 All rights reserved 4 The Bs Tutorial fifndef TABLE SIZE define TABLE SIZE 100 endif int table TABLE SIZE In this case if when arriving at this piece of code the TABLE SIZE macro has not been defined yet it would be defined to a value of 100 If it already existed it would keep its previous value since the define directive would not be executed The if else and elif i e else if directives serve to specify some condition to be met in order for the portion of code they surround to be compiled The condition that follows if or elif can only evaluate constant expressions including macro expressions For example if TABLE SIZE gt 200 undef TABLE SIZE define TABLE SIZE 200 elif TABLE SIZE 50 undef TABLE SIZE define TABLE SIZE 50 else undef TABLE SIZE define TABLE SIZE 100 endif int table TABLE SIZE Notice how the whole structure of if elif and else chained directives ends with endif The behavior of ifdef and ifndef can also be achieved by using the special operators defined and defined respectively in any if or elif directive fif defined TABLE SIZE define TABLE SIZE 100 elif defined ARRAY SIZE fdefine TABLE SIZE ARRAY SIZE int table TABLE SI
145. ork we need to introduce the concept of variable Let us think that I ask you to retain the number 5 in your mental memory and then I ask you to memorize also the number 2 at the same time You have just stored two different values in your memory Now if I ask you to add 1 to the first number I said you should be retaining the numbers 6 that is 5 1 and 2 in your memory Values that we could now for example subtract and obtain 4 as result The whole process that you have just done with your mental memory is a simile of what a computer can do with two variables The same process can be expressed in C with the following instruction set a 5 b 2 asat I result a b Obviously this is a very simple example since we have only used two small integer values but consider that your computer can store millions of numbers like these at the same time and conduct sophisticated mathematical operations with them Therefore we can define a variable as a portion of memory to store a determined value Each variable needs an identifier that distinguishes it from the others for example in the previous code the variable identifiers were a b and result but we could have called the variables any names we wanted to invent as long as they were valid identifiers Identifiers A valid identifier is a sequence of one or more letters digits or underscore characters _ Neither spaces nor punctuation marks or symbols can be part of an identifie
146. otherwise the loop ends and statement is skipped not executed 3 statement is executed As usual it can be either a single statement or a block enclosed in braces 4 finally whatever is specified in the increase field is executed and the loop gets back to step 2 Here is an example of countdown using a for loop countdown using a for loop 4 Se Be Ve Op Sp Bp Bp d munda include lt iostream gt using namespace std int main owe sinc ecd isle iac di cout lt lt m ee et oye lt lt METREN return 0 The initialization and increase fields are optional They can remain empty but in all cases the semicolon signs between them must be written For example we could write for n 10 if we wanted to specify no initialization and no increase or for n lt 10 n if we wanted to include an increase field but no initialization maybe because the variable was already initialized before Optionally using the comma operator we can specify more than one expression in any of the fields included in a for loop like in initialization for example The comma operator is an expression separator it serves to separate more than one expression where only one is generally expected For example suppose that we wanted to initialize more than one variable in our loop for C m O cue E gml Lh E ier w whatever here This loop will execute for 50 times if neither n or i are modified within the
147. our function template with two objects of different types as arguments aliene aeg long 1 k GetMax i 1 This would not be correct since our GetMax function template expects two arguments of the same type and in this call to it we use objects of two different types We can also define function templates that accept more than one type parameter simply by specifying more template parameters between the angle brackets For example template class T class U T Gethin T a Ub 1 return a lt b a b In this case our function template GetMin accepts two parameters of different types and returns an object of the same type as the first parameter T that is passed For example after that declaration we could call GetMin with ae ibo 18 domes ly i GetMin lt int long gt 3 1 or simply i GetMin j 1 even though j and 1 have different types since the compiler can determine the appropriate instantiation anyway 115 eplusplus com 2008 All rights reserved 4 The enge Tutorial Class templates We also have the possibility to write class templates so that a class can have members that use template parameters as types For example template class T class mypair T values 2 publiek mypair T first T second values 0 first values 1 second he The class that we have just defined serves to store two elements of any valid type For example if we wanted to declare
148. out lt lt Number is even Mn else odd a This example is indeed not an example of efficiency I am sure that at this point you can already make a program with the same result but using only half of the code lines that have been used in this example Anyway this example illustrates how prototyping works Moreover in this concrete example the prototyping of at least one of the two functions is necessary in order to compile the code without errors The first things that we see are the declaration of functions odd and even Void Odd aint tai void even int a This allows these functions to be used before they are defined for example in main which now is located where some people find it to be a more logical place for the start of a program the beginning of the source code Anyway the reason why this program needs at least one of the functions to be declared before it is defined is because in odd there is a call to even and in even there is a call to odd If none of the two functions had been 52 eplusplus com 2008 All rights reserved 4 The enge Tutorial previously declared a compilation error would happen since either odd would not not be visible from even because it has still not been declared or even would not be visible from odd for the same reason Having the prototype of all functions together in the same place within the source code is found practical by some programmers and this can be e
149. p When we want to modify the value of a variable by performing an operation on the value currently stored in that variable we can use compound assignment operators expression is equivalent to value increase value value increase a 5 asa 5 a b a a b price units l price price units 1 and the same for all other operators For example 22 eplusplus com 2008 All rights reserved 4 The enge Tutorial compound assignment operators 8 include lt iostream gt using namespace std int main int a b 3 a b a 2y equivalent to a a 2 cout lt lt a return 0 Increase and decrease Shortening even more some expressions the increase operator and the decrease operator increase or reduce by one the value stored in a variable They are equivalent to 1 and to 1 respectively Thus Gtt ebd Genel g are all equivalent in its functionality the three of them increase by one the value of c In the early C compilers the three previous expressions probably produced different executable code depending on which one was used Nowadays this type of code optimization is generally done automatically by the compiler thus the three expressions should produce exactly the same executable code A characteristic of this operator is that it can be used both as a prefix and as a suffix That means that it can be written either
150. r Only letters digits and single underscore characters are valid In addition variable identifiers always have to begin with a letter They can also begin with an underline character _ but in some cases these may be reserved for compiler specific keywords or external identifiers as well as identifiers containing two successive underscore characters anywhere In no case they can begin with a digit Another rule that you have to consider when inventing your own identifiers is that they cannot match any keyword of the C language nor your compiler s specific ones which are reserved keywords The standard reserved keywords are asm auto bool break case catch char class const const cast continue default delete do double dynamic cast else enum explicit export extern false float for friend goto if inline int long mutable namespace new operator private protected public register reinterpret cast return short signed sizeof static static cast struct switch template this throw true try typedef typeid typename union unsigned using virtual void volatile wchar t while Additionally alternative representations for some operators cannot be used as identifiers since they are reserved words under some circumstances and and eq bitand bitor compl not not eq or or eq xor xor eq 11 eplusplus com 2008 All rights reserved 4 The Crt Lageugee Tutorial Your compiler may
151. r was followed by an ampersand sign amp This ampersand is what specifies that their corresponding arguments are to be passed by reference instead of by value When a variable is passed by reference we are not passing a copy of its value but we are somehow passing the variable itself to the function and any modification that we do to the local variables will have an effect in their counterpart variables passed as arguments in the call to the function 47 eplusplus com 2008 All rights reserved 4 The cr e Tutorial void duplicate int amp a int amp b int amp c Fb duplicate x y z Y To explain it in another way we associate a b and c with the arguments passed on the function call x y and z and any change that we do on a within the function will affect the value of x outside it Any change that we do on b will affect y and the same with c and z That is why our program s output that shows the values stored in x y and z after the call to duplicate shows the values of all the three variables of main doubled If when declaring the following function vod duplicate ints ja inte b ante ic we had declared it this way Nioalel ichijelsveciee Gis ai Wit Io alee i e without the ampersand signs amp we would have not passed the variables by reference but a copy of their values instead and therefore the output on screen of our program would have been the values of x y and z without
152. r example now we can create a function member of the abstract base class CPolygon that is able to print on screen the result of the area function even though CPolygon itself has no implementation for this function 110 eplusplus com 2008 All rights reserved 4 The enge Tutorial pure virtual members can be called 20 from the abstract base class 10 include lt iostream gt using namespace std class CPolygon protected int width height jeibllo lbabre p void set values int a int b width a height b virtual int area void 0 void printarea void cout lt lt this gt area lt lt endl lg class CRectangle public CPolygon pupeles int area void return width height Ig class CTriangle publie CPolyqon jeibllonkutieg int area void return width height 2 hi int main CRectangle rect Triangle trol CPolygon ppolyl amp rect CPolygon ppoly2 amp trgl ppolyl set values 4 5 ppoly2 set values 4 5 ppolyl printarea ppoly2 printarea return 0 Virtual members and abstract classes grant C the polymorphic characteristics that make object oriented programming such a useful instrument in big projects Of course we have seen very simple uses of these features but these features can be applied to arrays of objects or dynamically allocated objects Let s end with the same example again but this time with objects that are
153. r function Global function a amp lw tt A operator operator A a A operator int operator A int a b R lt gt I lt gt lt lt gt gt amp amp A operator B operator A B a b amp lt lt gt gt A operator B a b c Q A operator B C a x gt A operator gt Where a is an object of class A b is an object of class B and c is an object of class c You can see in this panel that there are two ways to overload some class operators as a member function and as a global function Its use is indistinct nevertheless I remind you that functions that are not members of a class cannot access the private or protected members of that class unless the global function is its friend friendship is explained later The keyword this The keyword this represents a pointer to the object whose member function is being executed It is a pointer to the object itself 97 eplusplus com 2008 All rights reserved 4 The iy Tutorial One of its uses can be to check if a parameter passed to a member function is the object itself For example this yes amp a is b include lt iostream gt using namespace std class CDummy public int isitme CDummy amp param int CDummy isitme CDummy amp param if amp param this return true else return false int main CDummy a CDummy
154. rate since it is not what we were expecting from the user So when you use the data input provided by cin extractions you will have to trust that the user of your program will be cooperative and that he she will not introduce his her name or something similar when an integer value is requested A little ahead when we see the stringstream class we will see a possible solution for the errors that can be caused by this type of user input You can also use cin to request more than one datum input from the user cin 5 a gt be is equivalent to Gilg SS a gua 2 lop In both cases the user must give two data one for variable a and another one for variable p that may be separated by any valid blank separator a space a tab character or a newline cin and strings We can use cin to get strings with the extraction operator as we do with fundamental data type variables Em mys Er ing However as it has been said cin extraction stops reading as soon as if finds any blank space character so in this case we will be able to get just one word for each extraction This behavior may or may not be what we want for example if we want to get a sentence from the user this extraction operation would not be useful In order to get entire lines we can use the function getline which is the more recommendable way to get user input with cin 31 cplusplus com 2008 All rights reserved 4 The cr e Tutorial cin with s
155. rators and in the replacement sequence If the operator is used before a parameter is used in the replacement sequence that parameter is replaced by a string literal as if it were enclosed between double quotes define str x x Cowie Siew eet g This would be translated into outta sits The operator concatenates two arguments leaving no blank spaces between them define glue a b a f4 b glue c out test This would also be translated into cout lt lt test Because preprocessor replacements happen before any C syntax check macro definitions can be a tricky feature but be careful code that relies heavily on complicated macros may result obscure to other programmers since the syntax they expect is on many occasions different from the regular expressions programmers expect in C Conditional inclusions ifdef Zifndef if Zendif Zelse and elif These directives allow to include or discard part of the code of a program if a certain condition is met ifdef allows a section of a program to be compiled only if the macro that is specified as the parameter has been defined no matter which its value is For example ifdef TABLE SIZE int table TABLE SIZE B endif In this case the line of code int table TABLE SIZE is only compiled if TABLE SIZE was previously defined with define independently of its value If it was not defined that line will not be included in the program compilati
156. rators that can be used in C 23 eplusplus com 2008 All rights reserved 4 The cr e Tutorial Equal to Not equal to Greater than Less than Greater than or equal to Less than or equal to I AIVIATV J Il Here there are some examples y e 5 evaluates to false 5 gt A evaluates to true 3 2 evaluates to true 6 gt 6 evaluates to true B lt 5 evaluates to false Of course instead of using only numeric constants we can use any valid expression including variables Suppose that a 2 b 3 and c 6 a 5 evaluates to false since a is not equal to 5 a b gt c evaluates to true since 2 3 gt 6 is true b 4 gt a c evaluates to false since 3 4 gt 2 6 is false b 2 a evaluates to true Be careful The operator one equal sign is not the same as the operator two equal signs the first one is an assignment operator assigns the value at its right to the variable at its left and the other one is the equality operator that compares whether both expressions in the two sides of it are equal to each other Thus in the last expression b 2 a we first assigned the value 2 to b and then we compared it to a that also stores the value 2 so the result of the operation is true Logical operators amp amp The Operator is the C operator to perform the Boolean operation NOT it has only on
157. re lines with directives for the compiler s preprocessor those beginning by 4 Then there were lines that began the declaration of a function in this case the main function and finally lines with statements like the insertion into cout which were all included within the block delimited by the braces of the main function The program has been structured in different lines in order to be more readable but in C we do not have strict rules on how to separate instructions in different lines For example instead of int main Sene He cNWordc return 0 We could have written abate main 0 db Coble lt lt lt He Mior Wor Va sexes Op Ji All in just one line and this would have had exactly the same meaning as the previous code In C the separation between statements is specified with an ending semicolon at the end of each one so the separation in different code lines does not matter at all for this purpose We can write many statements per line or write a single statement that takes many code lines The division of code in different lines serves only to make it more legible and schematic for the humans that may read it Let us add an additional instruction to our first program cplusplus com 2008 All rights reserved 4 The cr e Tutorial my second program in CFF Hello World I m a C program include iostream using namespace std int main cout Hello World cout
158. rints out the array to know the range to iterate in the passed array without going out of range In a function declaration it is also possible to include multidimensional arrays The format for a tridimensional array parameter is base type depth depth for example a function with a multidimensional array as argument could be void procedure int myarray 3 4 Notice that the first brackets are left blank while the following ones are not This is so because the compiler must be able to determine within the function which is the depth of each additional dimension Arrays both simple or multidimensional passed as function parameters are a quite common source of errors for novice programmers I recommend the reading of the chapter about Pointers for a better understanding on how arrays operate 59 eplusplus com 2008 All rights reserved 4 The cH Lageugee Tutorial Character Sequences As you may already know the C Standard Library implements a powerful string class which is very useful to handle and manipulate strings of characters However because strings are in fact sequences of characters we can represent them also as plain arrays of char elements For example the following array char jenny 20 is an array that can store up to 20 elements of type char It can be represented as jenny Therefore in this array in theory we can store sequences of characters up to 20 characters long Bu
159. ry Combining object construction and stream opening in a single statement Both forms to open a file are valid and equivalent To check if a file stream was successful opening a file you can do it by calling to member is open with no arguments This member function returns a bool value of true in the case that indeed the stream object is associated with an open file or false otherwise if myfile is open ok proceed with output 139 eplusplus com 2008 All rights reserved 4 The enge Tutorial Closing a file When we are finished with our input and output operations on a file we shall close it so that its resources become available again In order to do that we have to call the stream s member function close This member function takes no parameters and what it does is to flush the associated buffers and close the file myfile close Once this member function is called the stream object can be used to open another file and the file is available again to be opened by other processes In case that an object is destructed while still associated with an open file the destructor automatically calls the member function close Text files Text file streams are those where we do not include the ios binary flag in their opening mode These files are designed to store text and thus all values that we input or output from to them can suffer some formatting transformations which do not necessarily
160. s access specifier describes the minimum access level for the members that are inherited from the base class 102 eplusplus com 2008 All rights reserved 4 The enge Tutorial derived classes include lt iostream gt 20 10 using namespace std class CPolygon i protected int width height jeiullelabrerg iod dasetevalluesqmtearemiti width a height b hi class CRectangle public CPolygon papine int area return width height class CTriangle public CPolygon polo er int area return width height 2 ine main 0 Y CRectangle rect CTriangle trgl rect set values y ieEgilesetaevallesq 5r cout rect area endl cout trgl area endl return 0 The objects of the classes CRectangle and CTriangle each contain members inherited from CPolygon These are width height and set values The protected access specifier is similar to private Its only difference occurs in fact with inheritance When a class inherits from another one the members of the derived class can access the protected members inherited from the base class but not its private members Since we wanted width and height to be accessible from members of the derived classes CRectangle and CTriangle and not only by members of CPolygon we have used protected access instead of private We can summarize the different access types according to who can access them in the following w
161. s strings The C language library provides support for strings through the standard string class This is not a fundamental type but it behaves in a similar way as fundamental types do in its most basic usage 15 eplusplus com 2008 All rights reserved 4 The enge Tutorial A first difference with fundamental data types is that in order to declare and use objects variables of this type we need to include an additional header file in our source code string and have access to the std namespace which we already had in all our previous programs thanks to the using namespace statement Hil my EirsEe sering mimis dS my STENE include lt iostream gt include lt string gt using namespace std int main String mystrlng This is a string cout mystring return 0 As you may see in the previous example strings can be initialized with any valid string literal just like numerical type variables can be initialized to any valid numerical literal Both initialization formats are valid with strings string mystring This is s string String mystring This is a string Strings can also perform all the other basic operations that fundamental data types can like being declared without an initial value and being assigned values during execution JL my ee se stering This is the initial string content include lt iostream gt This is a different string content include lt string gt using namespa
162. s to perform output and input of characters to from files e ofstream Stream class to write on files e ifstream Stream class to read from files e fstream Stream class to both read and write from to files These classes are derived directly or indirectly from the classes istream and ostream We have already used objects whose types were these classes cin is an object of class istream and cout is an object of class ostream Therfore we have already been using classes that are related to our file streams And in fact we can use our file streams the same way we are already used to use cin and cout with the only difference that we have to associate these streams with physical files Let s see an example basic file operations file example txt include lt iostream gt Writing this to a file include lt fstream gt using namespace std int main ofstream myfile myfile open example txt myfile lt lt Writing this to a file n myfile close return 0 This code creates a file called example txt and inserts a sentence into it in the same way we are used to do with cout but using the file stream myfile instead But let s go step by step Open a file The first operation generally performed on an object of one of these classes is to associate it to a real file This procedure is known as to open a file An open file is represented within a program by a stream object an instantiation of one of these classes in th
163. same if we write mychar mychar 1 myshort myshort 1 mylong mylong 1 Both the increase and decrease operators have greater operator precedence than the dereference operator but both have a special behavior when used as suffix the expression is evaluated with the value it had before being increased Therefore the following expression may lead to confusion kar Because has greater precedence than this expression is equivalent to p Therefore what it does is to increase the value of p so it now points to the next element but because is used as postfix the whole expression is evaluated as the value pointed by the original reference the address the pointer pointed to before being increased Notice the difference with p Here the expression would have been evaluated as the value pointed by p increased by one The value of p the pointer itself would not be modified what is being modified is what it is being pointed to by this pointer If we write Soni Sears Because has a higher precedence than both p and q are increased but because both increase operators are used as postfix and not prefix the value assigned to p is q before both p and q are increased And then both are increased It would be roughly equivalent to Like always I recommend you to use parentheses in order to avoid unexpected results and to give more legibility to the code cpl
164. ss a complete block of memory by value as a parameter to a function but we are allowed to pass its address In practice this has almost the same effect and it is a much faster and more efficient operation In order to accept arrays as parameters the only thing that we have to do when declaring the function is to specify in its parameters the element type of the array an identifier and a pair of void brackets For example the following function void procedure int arg accepts a parameter of type array of int called arg In order to pass to this function an array declared as int myarray 40 it would be enough to write a call like this procedure myarray Here you have a complete example arrays as parameters 5 10 15 include lt iostream gt 24 6 8 10 using namespace std void printarray int arg int length for int n 0 n length ntt gw lt lt swa e Mp ewe KK UM E int main inte firstarray 5 10 15r int secondarray ill 127 2 10 8 cp OT printarray firatarray 3 printarray secondarray 5 return 0 As you can see the first parameter int arg accepts any array whose elements are of type int whatever its length For that reason we have included a second parameter that tells the function the length of each array that 58 cplusplus com 2008 All rights reserved 4 The enge Tutorial we pass to it as its first parameter This allows the for loop that p
165. ss and they can only be referred from within other members of that same class Here is the complete example of class CRectangle classes example area 12 include lt iostream gt using namespace std class CRectangle Ie x ws pubic void set_values int int int area return x y vorde Rectangle setivaluesk Ontan me D x 8 y b int main CRectangle rect rect set values 3 4 cout lt lt area lt lt rect area return 0 The most important new thing in this code is the operator of scope two colons included in the definition of set values It is used to define a member of a class from outside the class definition itself You may notice that the definition of the member function area has been included directly within the definition of the CRectangle class given its extreme simplicity whereas set values has only its prototype declared within the class but its definition is outside it In this outside declaration we must use the operator of scope to specify that we are defining a function that is a member of the class CRectangle and not a regular global function The scope operator specifies the class to which the member being declared belongs granting exactly the same Scope properties as if this function definition was directly included within the class definition For example in the function set values of the previous code we have been able to use the var
166. std So in order to access its functionality we declare with this expression that we will be using these entities This line is very frequent in C programs that use the standard library and in fact it will be included in most of the source codes included in these tutorials int main This line corresponds to the beginning of the definition of the main function The main function is the point by where all C programs start their execution independently of its location within the source code It does not matter whether there are other functions with other names defined before or after it the instructions contained within this function s definition will always be the first ones to be executed in any C program For that same reason it is essential that all C programs have a main function The word main is followed in the code by a pair of parentheses That is because it is a function declaration In C what differentiates a function declaration from other types of expressions are these parentheses that follow its name Optionally these parentheses may enclose a list of parameters within them Right after these parentheses we can find the body of the main function enclosed in braces What is contained within these braces is what the function does when it is executed eplusplus com 2008 All rights reserved 4 The cr e Tutorial cout Hello World This line is a C statement A statement is a simple or
167. step 3 condition is false ignore statement and continue after it to step 5 3 Execute statement cout n sens prints the value of n on the screen and decreases n by 1 End of block Return automatically to step 2 5 Continue the program right after the block print FIRE and end program When creating a while loop we must always consider that it has to end at some point therefore we must provide within the block some method to force the condition to become false at some point otherwise the loop will continue looping forever In this case we have included n that decreases the value of the variable that is being evaluated in the condition n by one this will eventually make the condition n gt 0 to become false after a certain number of loop iterations to be more specific when n becomes 0 that is where our while loop and our countdown end Of course this is such a simple action for our computer that the whole countdown is performed instantly without any practical delay between numbers The do while loop Its format is do statement while condition Its functionality is exactly the same as the while loop except that condition in the do while loop is evaluated after the execution of statement instead of before granting at least one execution of statement even if condition is never fulfilled For example the following example program echoes any number you enter until you enter 0 number echoer Enter nu
168. stvalue is 10 include lt iostream gt secondvalue is 20 using namespace std int main int firstvalue secondvalue int mypolnter mypointer amp firstvalue mypointer 10 mypointer amp secondvalue mypointer 20 cout firstvalue is firstvalue endl cout secondvalue is secondvalue endl return 0 Notice that even though we have never directly set a value to either firstvalue Or secondvalue both end up with a value set indirectly through the use of mypointer This is the procedure First we have assigned as value of mypointer a reference to firstvalue using the reference operator amp And then we have assigned the value 10 to the memory location pointed by mypointer that because at this moment is pointing to the memory location of firstvalue this in fact modifies the value of firstvalue In order to demonstrate that a pointer may take several different values during the same program I have repeated the process with secondvalue and that same pointer mypointer Here is an example a little bit more elaborated more pointers firstvalue is 10 include lt iostream gt secondvalue is 20 using namespace std bime awena C int firstvalue 5 secondvalue 15 ige oly EP pl amp firstvalue pl address of firstvalue p2 amp secondvalue p2 address of secondvalue pl 10 value pointed by pl 10 p2 pl value pointed by p2 value poi
169. t lt s is 1 cout x is 1 k s else if x 2 case iaz cout lt lt x is 2 cout x is 2 break Bls 4 default cout value of x unknown COUE Se NGHE OE ene E MEM MC The switch statement is a bit peculiar within the C language because it uses labels instead of blocks This forces us to put break statements after the group of statements that we want to be executed for a specific condition Otherwise the remainder statements including those corresponding to other labels will also be executed until the end of the switch selective block or a break statement is reached For example if we did not include a break statement after the first group for case one the program will not automatically jump to the end of the switch selective block and it would continue executing the rest of statements until it reaches either a break instruction or the end of the switch selective block This makes unnecessary to include braces surrounding the statements for each of the cases and it can also be useful to execute the same block of instructions for different possible values for the expression being evaluated For example switch x case 1 case 2 case 3 owe e Wse abs Jl 2 gue Se break default cout lt lt Wes SiG eene dis 2 por o 1 Notice that switch can only be used to compare an expression against constants Therefore we cannot put variables as labels for example
170. t to 5 gt pointer to member right m ee Left to 6 multiplicative right g a Left to 7 additive right 8 K lt gt gt shift Left to right no Left to 9 PE ES relational right Left to l 10 equality right TNT Left to 11 bitwise AND right 12 bitwise XOR uad right A Left to 13 bitwise OR right Left to amp amp 14 logical AND right A Left to 15 HI logical OR right a Right to i 16 2 conditional left ke AS jas Right to 17 gt gt lt lt amp assignment left Left to 18 comma right Grouping defines the precedence order in which operators are evaluated in the case that there are several operators of the same level in an expression All these precedence levels for operators can be manipulated or become more legible by removing possible ambiguities using parentheses signs and as in this example a 54 7 S23 27 eplusplus com 2008 All rights reserved ji 4 The enge Tutorial might be written either as or 5 w T o 2r w ll depending on the operation that we want to perform So if you want to write complicated expressions and you are not completely sure of the precedence levels always include parentheses It will also become a code easier to read 28 eplusplus com 2008 All rights reserved 4 The Bs Tutorial Basic Input Output Until now the example programs of previous sections provided
171. t we can also store shorter sequences For example jenny could store at some point in a program either the sequence Hello or the sequence Merry christmas since both are shorter than 20 characters Therefore since the array of characters can store shorter sequences than its total length a special character is used to signal the end of the valid sequence the null character whose literal constant can be written as 0 backslash zero Our array of 20 elements of type char called jenny can be represented storing the characters sequences Hello and Merry Christmas as Notice how after the valid content a null character 0 has been included in order to indicate the end of the sequence The panels in gray color represent char elements with undetermined values Initialization of null terminated character sequences Because arrays of characters are ordinary arrays they follow all their same rules For example if we want to initialize an array of characters with some predetermined sequence of characters we can do it just like any other array ehan nee 4 We Uu UqU Ma WU UNQU je In this case we would have declared an array of 6 elements of type char initialized with the characters that form the word Hello plus a null character 0 at the end But arrays of char elements have an additional method to initialize their values using string literals In the expressions we have used in some examples in previous chapters const
172. template When projects grow it is usual to split the code of a program in different source code files In these cases the interface and implementation are generally separated Taking a library of functions as example the interface generally consists of declarations of the prototypes of all the functions that can be called These are generally declared in a header file with a h extension and the implementation the definition of these functions is in an independent file with c code Because templates are compiled when required this forces a restriction for multi file projects the implementation definition of a template class or function must be in the same file as its declaration That means that we cannot separate the interface in a separate header file and that we must include both interface and implementation in any file that uses the templates Since no code is generated until a template is instantiated when required compilers are prepared to allow the inclusion more than once of the same template file with both declarations and definitions in a project without generating linkage errors 119 3 cplusplus com 2008 All rights reserved 4 The Bs Tutorial Namespaces Namespaces allow to group entities like classes objects and functions under a name This way the global scope can be divided in sub scopes each one with its own name The format of namespaces is namespace identifier entities Where
173. th exactly the same meaning with or without the keyword signed An exception to this general rule is the cnar type which exists by itself and is considered a different fundamental data type from signed char and unsigned char thought to store characters You should use either signed or unsigned if you intend to store numerical values in a char sized variable short and long can be used alone as type specifiers In this case they refer to their respective integer fundamental types short is equivalent to short int and long is equivalent to long int The following two variable declarations are equivalent short Year short int Year Finally signed and unsigned may also be used as standalone type specifiers meaning the same as signed int and unsigned int respectively The following two declarations are equivalent unsigned NextYear unsigned int NextYear To see what variable declarations look like in action within a program we are going to see the C code of the example about your mental memory proposed at the beginning of this section 13 eplusplus com 2008 All rights reserved 4 The cH agure Tutorial operating with variables 4 include lt iostream gt using namespace std int main declaring variables int a Di int result process a 5 b 2 el a qe lg result a b print out the result cout lt lt result terminate the program return 0 Do not worry
174. that can be performed by reinterpret cast but not by static cast have no specific uses in C are low level operations whose interpretation results in code which is generally system specific and thus non portable For example class A alias A a new A Beebe reinterpret eaS EAB ay This is valid C code although it does not make much sense since now we have a pointer that points to an object of an incompatible class and thus dereferencing it is unsafe const_cast This type of casting manipulates the constness of an object either to be set or to be removed For example in order to pass a const argument to a function that expects a non constant parameter 130 eplusplus com 2008 All rights reserved 4 The enge Tutorial const cast sample text include lt iostream gt using namespace std vordiprine echar ASEE ClownE quse lt lt Fondi int main const char lt c o sample text printi ecnst icase ehar ie CDE return 0 typeid typeid allows to check the type of an expression typeid expression This operator returns a reference to a constant object of type type info that is defined in the standard header file lt typeinfo gt This returned value can be compared with another one using operators and or can serve to obtain a null terminated character sequence representing the data type or class name by using its name member typeid a and b are of different t
175. then assign b 2 to variable a So at the end variable a would contain the value 5 while variable b would contain value 3 Bitwise Operators amp lt lt gt gt Bitwise operators modify variables considering the bit patterns that represent the values they store operatorjasm equivalent description amp AND Bitwise AND OR Bitwise Inclusive OR b XOR Bitwise Exclusive OR NOT Unary complement bit inversion lt lt SHL Shift Left gt gt SHR Shift Right Explicit type casting operator Type casting operators allow you to convert a datum of a given type to another There are several ways to do this in C The simplest one which has been inherited from the C language is to precede the expression to be converted by the new type enclosed between parentheses imt i float f 3 14 al ane f The previous code converts the float number 3 14 to an integer value 3 the remainder is lost Here the typecasting operator was int Another way to do the same thing in C is using the functional notation preceding the expression to be converted by the type and enclosing the expression between parentheses X xw 3 e Both ways of type casting are valid in C sizeof This operator accepts one parameter which can be either a type or a variable itself and returns the size in bytes of that type or object a sizeof char This will assign the value 1 to a because
176. they have been defined 3 14159 and n respectively The define directive is not a C statement but a directive for the preprocessor therefore it assumes the entire line as the directive and does not require a semicolon at its end If you append a semicolon character at the end it will also be appended in all occurrences within the body of the program that the preprocessor replaces Declared constants const With the const prefix you can declare constants with a specific type in the same way as you would do with a variable const int pathwidth 100 const char tabulator t Here pathwidth and tabulator are two typed constants They are treated just like regular variables except that their values cannot be modified after their definition 20 eplusplus com 2008 All rights reserved 4 The enge Tutorial Operators Once we know of the existence of variables and constants we can begin to operate with them For that purpose C integrates operators Unlike other languages whose operators are mainly keywords operators in C are mostly made of signs that are not part of the alphabet but are available in all keyboards This makes C code shorter and more international since it relies less on English words but requires a little of learning effort in the beginning You do not have to memorize all the content of this page Most details are only provided to serve as a later reference in case you need it
177. tion divide In the first one divide 12 we have only specified one argument but the function divide allows up to two So the function divide has assumed that the second parameter is 2 since that is what we have specified to happen if this parameter was not passed notice the function declaration which finishes with int b 2 not just int b Therefore the result of this function call is 6 12 2 In the second call divide 20 4 there are two parameters so the default value for b int b 2 is ignored and b takes the value passed as argument that is 4 making the result returned equal to 5 20 4 49 eplusplus com 2008 All rights reserved 4 The enge Tutorial Overloaded functions In C two different functions can have the same name if their parameter types or number are different That means that you can give the same name to more than one function if they have either a different number of parameters or different types in their parameters For example overloaded function 10 include iostream 2 5 using namespace std int operate int a int b return a b float operate float a float b return a b int main int x 5 y 2 float n 5 0 m 2 0 cout lt lt operate x y Conti KK UM E cout operate n m Conta WV E return 0 In this case we have defined two functions with the same name operate but one of them accepts two parameters of type int and the other on
178. to dereference to and for that reason we will always have to cast the address in the void pointer to some other pointer type that points to a concrete data type before dereferencing it One of its uses may be to pass generic parameters to a function 71 eplusplus com 2008 All rights reserved 4 The ci Tutorial increaser ive 603 include lt iostream gt using namespace std void increase void data int psize if psize sizeof char ehar pehar pehar ebat ti pehar else if psize sizeof int ane pint pine aine datar seed dense h int main char a x int b 1602 increase amp a sizeof a increase amp b sizeof b Colle a e UL W e dg KK Einelils return 0 sizeof is an operator integrated in the C language that returns the size in bytes of its parameter For non dynamic data types this value is a constant Therefore for example sizeof char is 1 because char type is one byte long Null pointer A null pointer is a regular pointer of any pointer type which has a special value that indicates that it is not pointing to any valid reference or memory address This value is the result of type casting the integer value zero to any pointer type Jut pr a Ole p has a null pointer value Do not confuse null pointers with void pointers A null pointer is a value that any pointer may take to represent that it is pointing to nowhere while a
179. trings What s your name Juan SouliA n include lt iostream gt Hello Juan SouliA A As include lt string gt What is your favorite team The Isotopes using namespace std I like The Isotopes too int main string mystr cout lt lt What s your name getline cin mystr couci K lt Wisiculilo V lt lt wars lt lt o Wap cout What is your favorite team getline cin mystr owe lt K ir jake U KK wwe lt K ew ws return 0 Notice how in both calls to getline we used the same string identifier mystr What the program does in the second call is simply to replace the previous content by the new one that is introduced stringstream The standard header file lt sstream gt defines a class called stringstream that allows a string based object to be treated as a stream This way we can perform extraction or insertion operations from to strings which is especially useful to convert strings to numerical values and vice versa For example if we want to extract an integer from a string we can write string mystr 1204 INERME stringstream mystr gt myint This declares a string object with a value of 1204 and an int object Then we use stringstrean s constructor to construct an object of this type from the string object Because we can use stringstream objects as if they were streams we can extract an integer from it as we would have done on cin by applying the extractor operator gt gt
180. ts parent s members plus its own For example we are going 101 eplusplus com 2008 All rights reserved P The enge Tutorial to suppose that we want to declare a series of classes that describe polygons like our CRectangle or like CTriangle They have certain common properties such as both can be described by means of only two sides height and base This could be represented in the world of classes with a class CPolygon from which we would derive the two other ones CRectangle and CTriangle The class CPolygon would contain members that are common for both types of polygon In our case width and height And CRectangle and CTriangle would be its derived classes with specific features that are different from one type of polygon to the other Classes that are derived from others inherit all the accessible members of the base class That means that if a base class includes a member A and we derive it to another class with another member called B the derived class will contain both members A and B In order to derive a class from another we use a colon in the declaration of the derived class using the following format class derived class name public base class name SAC ME Where derived class name is the name of the derived class and base class name is the name of the class on which it is based The public access specifier may be replaced by any one of the other access specifiers protected and private Thi
181. ts of this tutorial as a review of concepts since they mainly explain the C part of C There are slight differences in the C syntax for some C features so I recommend you its reading anyway The 4th part describes object oriented programming The 5th part mostly describes the new features introduced by ANSI C standard Structure of this tutorial The tutorial is divided in 6 parts and each part is divided on its turn into different sections covering a topic each one You can access any section directly from the section index available on the left side bar or begin the tutorial from any point and follow the links at the bottom of each section Many sections include examples that describe the use of the newly acquired knowledge in the chapter It is recommended to read these examples and to be able to understand each of the code lines that constitute it before passing to the next chapter A good way to gain experience with a programming language is by modifying and adding new functionalities on your own to the example programs that you fully understand Don t be scared to modify the examples provided with this tutorial that s the way to learn Compatibility Notes The ANSI C standard acceptation as an international standard is relatively recent It was first published in November 1997 and revised in 2003 Nevertheless the C language exists from a long time before 1980s Therefore there are many compilers which do not support all
182. ue for i so big that our system could not handle it For example when I tried to give a value of 1 billion to the How many numbers question my system could not allocate that much memory for the program and I got the text message we prepared for this case Error memory could not be allocated Remember that in the case that we tried to allocate the memory without specifying the nothrow parameter in the new expression an exception would be thrown which if it s not handled terminates the program It is a good practice to always check if a dynamic memory block was successfully allocated Therefore if you use the nothrow method you should always check the value of the pointer returned Otherwise use the exception method even if you do not handle the exception This way the program will terminate at that point without causing the unexpected results of continuing executing a code that assumes a block of memory to have been allocated when in fact it has not Dynamic memory in ANSI C Operators new and delete are exclusive of C They are not available in the C language But using pure C language and its library dynamic memory can also be used through the functions malloc calloc realloc and free which are also available in C including the lt cstdlib gt header file see cstdlib for more info The memory blocks allocated by these functions are not necessarily compatible with those returned by new so each one should be manipulated with its own
183. ught by a regular int type handler If this throw specifier is left empty with no type this means the function is not allowed to throw exceptions Functions with no tnrow specifier regular functions are allowed to throw exceptions with any type int myfunction int param throw no exceptions allowed int myfunction int param all exceptions allowed Standard exceptions The C Standard library provides a base class specifically designed to declare objects to be thrown as exceptions It is called exception and is defined in the exception header file under the namespace std This class has the usual default and copy constructors operators and destructors plus an additional virtual member function called what that returns a null terminated character sequence char and that can be overwritten in derived classes to contain some sort of description of the exception 124 eplusplus com 2008 All rights reserved 4 The cr e Tutorial standard exceptions My exception happened include lt iostream gt include lt exception gt using namespace std class myexception public exception virtual const char what const throw return My exception happened myex int main Ery throw myex catch exception amp e cout lt lt e what lt lt endl return 0 We have placed a handler that catches exception objects by reference notice the ampersand after the type
184. us also hold function members The default access in union classes is public 94 eplusplus com 2008 All rights reserved 4 The enge Tutorial Classes II Overloading operators C incorporates the option to use standard operators to perform operations with classes in addition to with fundamental types For example int ar Joy ein a boo This is obviously valid code in C since the different variables of the addition are all fundamental types Nevertheless it is not so obvious that we could perform an operation similar to the following one struct i SECI Produce float price I ar dos a beo In fact this will cause a compilation error since we have not defined the behavior our class should have with addition operations However thanks to the C feature to overload operators we can design classes able to perform operations using standard operators Here is a list of all the operators that can be overloaded Overloadable operators n E lt gt J KK gt lt lt gt gt l lt gt E amp e amp ee amp amp 6 0 gt gt new delete new delete To overload an operator in order to use it with classes we declare operator functions which are regular functions whose names are the operator keyword followed by the operator sign that we want to overload The format is type operator sign parameters Here you have an examp
185. usplus com 2008 All rights reserved 4 The enge Tutorial Pointers to pointers C allows the use of pointers that point to pointers that these in its turn point to data or even to other pointers In order to do that we only need to add an asterisk for each level of reference in their declarations ehar a ehar AD ehar Cere o a tat b amp a g amp b This supposing the randomly chosen memory locations for each variable of 7230 8092 and 10502 could be represented as a b c EN 7230 2092 7230 8092 10502 The value of each variable is written inside each cell under the cells are their respective addresses in memory The new thing in this example is variable c which can be used in three different levels of indirection each one of them would correspond to a different value e chastype char and a value of 8092 e xc has type char and a value of 7230 e c has type char and a value of z void pointers The void type of pointer is a special type of pointer In C void represents the absence of type so void pointers are pointers that point to a value that has no type and thus also an undetermined length and undetermined dereference properties This allows void pointers to point to any data type from an integer value or a float to a string of characters But in exchange they have a great limitation the data pointed by them cannot be directly dereferenced which is logical since we have no type
186. vie gt year cout lt lt nYou have entered n cout lt lt pmovie gt title Cout lt lt W H c povie ayee lt lt BINE return 0 The previous code includes an important introduction the arrow operator gt This is a dereference operator that is used exclusively with pointers to objects with members This operator serves to access a member of an object to which we have a reference In the example we used pmovie gt title Which is for all purposes equivalent to pmovie title Both expressions pmovie gt title and pmovie title are valid and both mean that we are evaluating the member title of the data structure pointed by a pointer called pmovie It must be clearly differentiated from pmovie title which is equivalent to pmovie title And that would access the value pointed by a hypothetical pointer member called titie of the structure object pmovie which in this case would not be a pointer The following panel summarizes possible combinations of pointers and structure members 80 eplusplus com 2008 All rights reserved 4 The cr e Tutorial Expression What is evaluated Equivalent a b Member b of object a a gt b Member b of object pointed by a a b a b Value pointed by member b of object a a b Nesting structures Structures can also be nested so that a valid element of a structure can also be in its turn another structure Structemoviesstel Sering
187. w lt lt im lt lt Ww We owe lt lt Wists inl e return 0 The goto statement goto allows to make an absolute jump to another point in the program You should use this feature with caution since its execution causes an unconditional jump ignoring any type of nesting limitations The destination point is identified by a label which is then used as an argument for the goto statement A label is made of a valid identifier followed by a colon Generally speaking this instruction has no concrete use in structured or object oriented programming aside from those that low level programming fans may find for it For example here is our countdown loop using goto 38 eplusplus com 2008 All rights reserved 4 The enge Tutorial goto loop example 1j 9 G Y 6 5j Be Sp 3S5 ip BOIA include lt iostream gt using namespace std int main int n 10 loop owt x m lt lt Us Ws iF if n gt 0 goto loop Cour ETRE Natt return 0 The exit function exit is a function defined in the cstdlib library The purpose of exit is to terminate the current program with a specific exit code Its prototype is void exit int exitcode The exitcode is used by some operating systems and may be used by calling programs By convention an exit code of 0 means that the program finished normally and any other value means that some error or unexpected results happened The selective structure switch T
188. we are inventing right now in order to help clarify some concepts in this tutorial but in reality we cannot know before runtime the real value the address of a variable will have in memory Consider the following code fragment andy 25i fred andy ted amp andy The values contained in each variable after the execution of this are shown in the following diagram andy 9 1775 1776 1777 4 N fred i i ted i First we have assigned the value 25 to andy a variable whose address in memory we have assumed to be 1776 63 l cplusplus com 2008 All rights reserved 4 The enge Tutorial The second statement copied to red the content of variable andy which is 25 This is a standard assignment operation as we have done so many times before Finally the third statement copies to tea not the value contained in andy but a reference to it i e its address which we have assumed to be 1776 The reason is that in this third assignment operation we have preceded the identifier andy with the reference operator amp so we were no longer referring to the value of andy but to its reference its address in memory The variable that stores the reference to another variable like ted in the previous example is what we call a pointer Pointers are a very powerful feature of the C language that has many uses in advanced programming Farther ahead we will see how this type of variable is used and declared
189. ypes include lt iostream gt El alg aligie include lt typeinfo gt is aeg ime using namespace std int main int t a b a 0 b 0 if typeid a typeid b cout lt lt a and b are of different types n cout lt lt a is lt lt typeid a name lt lt n Cout lt lt Wa lsa W lt lt typeid b mame lt lt mU return 0 When typeid is applied to classes typeid uses the RTTI to keep track of the type of dynamic objects When typeid is applied to an expression whose type is a polymorphic class the result is the type of the most derived complete object 131 eplusplus com 2008 All rights reserved ji 4 The enge Tutorial typeid polymorphic class a is class CBase include lt iostream gt g ss class Ciase include lt typeinfo gt a is class CBase include exception b rs class CDerived using namespace std elass Base vat to eon T class CDerived public CBase nimitsgemamee O try CBase a new CBase CBase b new CDerived Gout lt lt a adiss e ccypeadia sname messe Nn Come lt lt o abes W lt lt civjssicl le cis lt lt sU E onte app eddo smamemEs ne Cont lt Waa ies W aa wrocic eb omame Es mE catch exception amp e cout lt lt Exception lt lt e what lt lt endl return 0 Notice how the type that typeid considers for pointers is the pointer type itself both a and b are of type class CBase

The C++ Language Tutorial

Contents

Download Pdf Manuals

Related Search

Related Contents