chapter 2 objects and classes

Prof.Manoj S. Kavedia (9860174297) ([email protected])

Class and ObjectQ1.What is class? How they are defined ?Describe themAns. A class is a way to bind the data and its associated functions together. It allows the data (and functions) to be hidden, if necessary, from external use. When defining a class, we are a new abstract data type that can be treated like any other built-in data type. Generally, a class specification has two parts:

1. Class declaration2. Class function definitions

The class declaration describes the type and scope of its members. The class functions definitions describe below the class functions are implemented.The general form of a class declaration is:

class class_name{

private:variable declarations; //data membersfunction declarations; //member function

public:variable declarations; //data memberfunction declaration; // member Function

} ;

The class declaration is similar to a struct declaration. The keyword class specifies, that what follows is an abstract data of type class_name. The body of a class is enclosed within braces and terminated by a semicolon. The class body contains the declaration of variables and functions. These functions and variables are collectively called class members. They are usually grouped under two sections, namely, private and public to denote which of the members are private and which of them are public. The keywords private and public are known as visibility labels. These keywords are followed by a colon.

The class members that have been declared as private can be accessed only from within the class. On the other hand, public members can be accessed from outside the class also. The data hiding (using private declaration) is the key feature of object-oriented programming. The use of the keyword private is optional. By default, the members of a class are private. If both the labels are missing, then, by default, all the

22Object and Classes

SyllabusSpecifying a class, Defining member functions, Arrays within a class, Creating objects, memory allocation for objects, static data & member function, Arrays of objects, objects as function argument.

1


members are private. Such a class is completely hidden from the outside world and does not serve any purpose.

The variables declared inside the class are known as data members and the functions are known as member functions. Only the member functions can have access to the private data members and private functions. However, the public members (both functions and data) can be accessed from outside the class.

Q2.What are the different ways member function can be defined?Ans. Member functions can be defined in two places:

Outside the class definition. Inside the class definition.

Irrespective of the place of definition, the function should perform same task. Therefore, the code for the function body would be identical in both the cases. However, there is a subtle difference in the way the function header is defined.

Q3.What is scope resolution operator ?state its functionAns. The symbol :: is called the Scope Resolution Operator.

The scope resolution operator (::) in C++ is used to define the already declared member functions (in the header file with the .cpp or the .h extension) of a particular class. In the .cpp file one can define the usual global functions or the member functions of the class.

To differentiate between the normal functions and the member functions of the class, one needs to use the scope resolution operator (::) in between the class name and the member function name i.e. ship::foo() where ship is a class and foo() is a member function of the class ship.

The other uses of the resolution operator is to resolve the scope of a variable when the same identifier is used to represent a global variable, a local variable, and members of one or more class(es). If the resolution operator is placed between the class name and the data member belonging to the class then the data name belonging to the particular class is referenced.

If the resolution operator is placed in front of the variable name then the global variable is referenced. When no resolution operator is placed then the local variable is referenced.Example

#include int n = 12; // A global variableint main() { int n = 13; // A local variable cout


1. private and 2. public

To denote which of the members are private and which of them are public. The keywords private and public are known as visibility labels. These keywords are followed by a colon.

PrivateThe class members that have been declared as private can be accessed only from

within the class. Public

public members can be accessed from outside the class also.

As described above private data members of the class can be accessed through the public member functions only of the same class.

Object_name.function_name(actual_arguments)Is the syntax of accessing the data member of the class.

Following example is used to demonstrate the same#include#includeclass rectangle{ private : int len, br; public: void area_peri( )

{int a, p;a = len * br;p = 2 * (len +br);cout


}};

//Main Program.. void main( ){

rectangle r1,r2,r3; //define 3 objects of class rectangler1.setdata(10,20); //set data in elements of the objectr1.displaydata( ); //display the data set by setdata( )r1.area_peri( ); // calculates and print area and Perimeterr2.setdata(5,8); r2.displaydata( ); r2.area_peri( ); r3.getdata( ); //receive data from keyboard r3.displaydata( ); r3.area_peri( );

}

Q5.What do you mean by the term data member and member Function?Ans. The variables declared inside the class are known as data members and the functions are known as member functions. Only the member functions can have access to the private data members and private functions. However, the public members (both functions and data) can be accessed from outside the class. Example

class class_name{

private:variable declarations; //data membersfunction declarations; //member function

public:variable declarations; //data memberfunction declaration; // member Function

} ;

4


Q6.List some of the header files used in C++?Ans.

Q7.Differentiate between object and classesAns.Classes and objects are separate but related concepts. Every object belongs to a class and every class contains one or more related objects.

1. A Class is static. All of the attributes of a class are fixed before, during, and after the execution of a program. The attributes of a class don't change.

2. The class to which an object belongs is also (usually) static. If a particular object belongs to a certain class at the time that it is created then it almost certainly will still belong to that class right up until the time that it is destroyed.

3. An Object on the other hand has a limited lifespan. Objects are created and eventually destroyed. Also during that lifetime, the attributes of the object may undergo significant change.

SrNo Classes Object1 Class is template or Object is software construct which binds

5


blueprint , its states how object should be and Behave

data and logic or methods /functions together

2 Class is user defined data type

Object is run time entity of class

3. Class cannot be passed as argument or parameter

Object can be passed as argument or parameter

4. Class is group of a object that share common property

Object is real time entity of class

5. Class can define object Object cannot define class6. Example

Class Demo { int num; public void getData(int x) { num = x ; } public void display() { cout


5.Supports both overloaded functionsas well as overrided functions.

5.Supports only overloaded functions.

Q10.State the necessity of preprocessor directive? State importance of #include?Ans. A C++ (or C) compiler begins by invoking the preprocessor, a program that uses special statements, known as directives or control statements, that cause special compiler actions such as:

file inclusion, in which the file being preprocessed incorporates the contents of another file, exactly as if the included files text were actually part of the including file;

macro substitution, in which one sequence of text is replaced by another; conditional compilation, in which parts of the source files code can be eliminated

at compile time under certain circumstances.All preprocessor directives begin with the # symbol (known as pound or hash), which

must occur in the leftmost column of the line. A preprocessor directive that takes up more than one line needs a continuation symbol, n (backslash), as the very last character of every line except the last.

Following directive #include is used in the program. This directive causes the preprocessor to add the content of the iostream file to the program. It contains declaration for the identifier cout and the operator


private :int num; //Data Member

public :void getNumber() // Member Function inside Class

{cout num;

}void dispData()

{cout


Cout m >> n;

}void set :: display (void)

{cout


my_array[8] = 100; my_array[9] = 100;

Luckily the number appearing between the brackets doesn't have to be a numeric literal. It can be a valid identifier that represents an integer value. This could be either a variable, a constant, or an expression that evaluates to an integer value. For example, a faster way of initializing all the elements of my_array to 100 would be to declare an integer variable, set its value to 0, use it to index my_array, then increment the variable by one and repeat the process until all the elements were set to 100. The following C++ code will do exactly that:

for(int i = 0; i


for( i = SIZE - 1; i >= 0 ; i--){

cout


cout


void main ( ){

int i , j ; char letters[6][1] = { {'M'},{'i'},{'c'},{'k'},{'e'},{'y'} } ; cout


for (i=0 ; i


{temp = Arr[j];Arr[j] = Arr[j+1];Arr[j+1] = temp;

}

}}

//Displaying the content of the arraycout


}

//Displaying the content of the arraycout


number_of_year = noy;}

void calculate(){sint = )principle_Amount * rate_of_interest * number_of_year)}

void display(){

cout


user defined functions such As vectors, date and time. Program object should be chosen such that they match closely the real World object eg. Elements of computer user environment are windows, menus and graphics, objects.

The physical objects are automobile in graphics stimulation, electronic component in circuit designing. The match between programming objects and a real world objects is a good resulting Objects offering the revolution in programming.For example : students objects includes the data members and functions as given:

Objects : studentData :

Roll-on NameDate of birth

Functions :Total( ) Average( )Percentage( )

This variable is known as object. This variable will be the type of class declared. To create at object you need to write

Classname objectname;

in the function main()

After creating objectname object, all data members are member functions declared in class gets initialised and member functions can be called with the statement

objectname.function();

For Example this is class Class student

{ private :int roll;int mark1, mark2;float average;

public:void getData()

{ ---------- }void calculate()

{------------}void displayData()

{------------}}

Declaration of ObjectStudent S1 , S2[10] , *S3 ;S1 is object of class student.S2[100] is array of 10 object of class student.S3 is pointer to an object of class student.

18


Another way of Declaring ObjectObject can also be declared or defined by just placing their names immediately

after closing brace of class ie in the following wayClass employee

{------------------------------

} e1 , e2[10] , *e3;

Q27.List and describe the access specifiers used in OOPAns.The access specifiers used in OOP are as follows

1. public2. private3. protected

Private The members are accessible only by the member functions or friend functions.

Protected These members are accessible by the member functions of the class and the classes which are derived from this class.

Public Accessible by any external member.

Access control helps prevent you from using objects in ways they were not intended to be used. This protection is lost when explicit type conversions (casts) are performed.The default access to class members (members of a class type declared using the class keyword) is private; the default access to struct and union members is public. For either case, the current access level can be changed using the public, private, or protected.

Access Specifier in More detailsPrivate

Can be data or method members Are accessible ONLY through other methods of the same class where they are

declared Cannot be accessed through a class instance Will not be inherited

Public Can be data or method members Are accessible globally from any function/method outside the class they are

declared, across the application Are accessible ONLY through a valid instance of the class in which they are

declared

19


Protected Can be data and method members Exactly same as private members for all practical purposes, except for the

inheritance part These members are inherited by a child of the class in which they are declared Their behaviour in the child class depends on how the inheritance has been

defined If the inheritance is private, these are private in the child class, if it is public,

these are public in the child class, and if the inheritance in protected, these are protected in the child class thus allowing further inheritance.

Nesting of Member Function

Q28.What is Nesting of Member function describe with help of programAns. A member function of a class. Can be called only by an object of that class using a dot operator. A member function can be called by using its name inside another member function of the same class. This is known as nesting of member function.

# include class circle{ int r1 ; public :

void getdata ( ){

cout > r1 ;

} int area_circle()

{ int a ;

a = 3.14 r1 r1 ;return (a) ;

}

void putdata ( ){cout


c1 . getdata ( ) ;c1 . putdata ( ) ;

}Q29.Explain with diagram how memory allocation is done for an objectAns. An object is a combination of data member and member function. It might given an impression that when an object of particular class is created memory is allocated to both its data member and member function. This is partially true. When an object is created memory is allocates to the data member only and not to member function.

Actually the member function are created place in memory space only once when they are define as a part of class specification. Since all the objects belonging to that class are the same member function, no separate space is created.

However separate storage is allocated for every object data member since they contain different value it allows different object to handle their data in a manner that suits them.

The member functions are created and placed in the memory function only once when they are defined as a part of class. Since all objects are belonging to that class use the same member function & no separate memory is allocated for the member function of each object. When the objects are created only space for memory variables is allocated separately for each object i.e the member variables will hold different data values for different object as shown in the fig.

Class abc{

int a;int b;

public:void getdata( );void disp( );} a1, a2;

Static Data member and Member function

Q30.Explain what is static data member ? what are the characteristics of static data memberAns. Static Member variables are generally used to maintain values common to the entire class. Static Members are stored separately rather than as a part of an object. As they are associated with the class itself rather than with any class objects, they are also known as class variables.A static data member has certain special characteristics :

a. It is initialized to zero, when the first object of its class is created. b. No other initialization to such member is permitted.

display getdata

Common for all objects , memory allocated to function where defined

A2 object

a

bX

A1 object

a

bX

21


c. Only one copy of that member is created for the entire class and is shared by all object at that class.

d. It is visible only within the class.The syntax to define static data member is as follows :

class item{

public: static int count;

};

int item::count = 0; // definition outside class declaration

Static data members are not part of objects of a given class type; they are separate objects. As a result, the declaration of a static data member is not considered a definition. The data member is declared in class scope, but definition is performed at file scope.

Q31.Write C++ program to implement the working of static data membersAns . Definition out side the class as shown in the example.

Class record{

static int count;public:

void counter(){ count++;}

void disp();{

cout


The type and scope of each static member variables must be define outside the class as given in above example.

Count is initialize to 0. when first object r1 is created. The count is increment each time when the counter function is called. Since there is only one copy of all data shared by all the objects as given below.

While defining static variables some initial value can also be defined to variables by defining

int record::count=10;After execution of above program if count is initialized to 10. then output will be

11121213

Q32.Why static variables are called as class variableAns.Static Member variables are generally used to maintain values common to the entire class. Static Members are stored seperately rather than as a part of an object. They are associated with the class itself rather than with any class objects and therefore they are also known as class variables.

Q33.Explain what is static member function ? what are the characteristics of static member FunctionAns. Static Member Functions : Similar to static data members, a member function can also be defined as static. A member function that is declared static has the characteristics as follows

1. It can have access to only static members (functions or variables) declared in the same class.

2. To call static member function we need to write statement with the name of class.classname : : functionsname;

The statements written in the definition of static function can be invoked and variables defined, processed in it are having seperate copies of objects and can hold unique value for that object.

Q34.Write C++ program to implement the working of static members function Ans. class record

{ static int count;

public:static void counter();

{count++;cout


record :: counter();record :: counter();

}

Array of Objects

Q35.How an array of object can be created demonstrate with c++ programAns.Similar to Array of structure in C, we also can have array of variables (objects) that are of type class. Naturally, these variables are known as arrays of objects.As we create the object using class name, we need to write array variable name along with size of array along with class name.

Consider a following example : class product{

char model[20];float price;

public;void readdata();void dispdata();

};This is a class with name product, to create array of this class type, we can

write.product telephones[10]; or product entertainment[5];

Graphical representation telephone(0) telephone(1) ------- telephone(9)model price model price ------- model modelreadata() dispdata() readata() dispdata() ------- readata() dispdata()

So the array telephones with their respective prices.To access array values, we have to use usual array handling techniques. And to

connect it with object we can use telephone[i].model

and to call function we may write telephone[i].readdata();

An array of objects is stored inside the memory similar to n-dimensional array is C. Here also, the space for data items of the objects is created and member functions are stored separately and will be shared by all objects.

Array of Class Objects Class objects one similar to any other C++ data type in that you can declare

pointer to them and arrays of them.

The array notation is the same as that of an array of structures.

24


Program : Array of Objects

#include #include /*----------------------Class definition-----------------------*/

class student{

int roll_no;char name[20];

public : // prototypes declaredvoid set_data(int, char *);void print_data();

};

void student::set_data(int c, char *s){

roll_no = c;strcpy(name, s);

}void student::print_data()

{cout


Object as Argument to Function

Q36.Describe how an object can be passed argument to functionAns. The functions are subprograms, written along with main() program and we can pass values from main() program to these subprogram to get processed. These values are of primary data type in C, and built-in datatype in C++.As C++ is best supporter of Object Oriented Programming techniques, here object may be passed as argument to the function. This particular process can be done in two ways

1.A copy of the entire object is passed to the function.

2.Only the address of the object is transferred to the function.

The method of passing copy of object is known as pass-by-value in this case, if the changes are made to object after called in function, then there is no effect on original object.

The second method is known as call-by-reference. In this case, the address of object is passed, to the function, as argument. If any changes are made that directly reflects the original object but this method avoids duplication of object. This method is more efficient.

Q37.Write C++ program to implement Object as function argument?Ans. Example Objects as Function Arguments -by reference

#include #include

class Rational{

int numerator;int denominator;

public : void set(int, int); // prototypes declaredvoid print();void exchange (Rational*);

};void Rational::set(int a, int b)

{

26


numerator = a;denominator = b;

}

void Rational::print(){

cout


{numerator = a;denominator = b;

}void Rational::print()

{cout


{ //function definition

}example

inline int cube(int r){

return(r*r*r);}

On execution of this statement the values of called program.i.e double c= cube (3);Every time when a function is called the value of C is 27. Its far superior to the macros.

The benefits of inline function dimensions as the function grow inside that is if the statement definition is too long the compiler will treat as normal function.

Q40.List the situations were inline expansion may not workAns. It may not work for the following expansion.

1. Functions returning values if the loop or goto exists.2. If the function contains static variable.3.If inline functions are recursive.4.If they contain return statement though defined as void function.(A void function can

have return statement)

Q41.Describe how function defined outside the class can be made INLINE. Demonstrate with program code.Ans.One of main objective of OOP is to separate the details of implementation from the class definition.It is therefore good practice to define the member function outside the class.

One can define a member function outside the class definition and still make it inline by just using the keyword or qualifier inline in the header line if the function definition.It is as demonstrated in the program below

Example/* Inline Member Functions */#include #include

/*----------------------Class definition-------------------------*/class sample{

int a;public :

// inline member functionsvoid setdata(int x){ a = x;}void print_square()

{cout


}

void print_cube();};

// inline member function

inline void sample::print_cube(){

cout


Return(S3);}

void dispData(){

cout


{ time t;t.ss=t1.ss+t2.ss;t.mm=t1.mm+t2.mm+t.ss/60;t.ss=t.ss%60;t.hh=t1.hh+t2.hh+t.mm/60;t.mm=t1.mm+t2.mm+1; }

return t;}};void main()

{ int r;r.getd();r.disp();getch(); }

Create a class distance having data members feet & inches add two distance & display the resultant distance in proper format. Initialize the objects with proper feets & inches.

Class distance{

int feet,inch;public:void getd(int f, int I)

{feet=f;inch=I;

}void display()

{ cout


Output16 8

Program-2Maintain the record of students and give the total marks for 3 subjects and calculate the average for each student and displays the contents on screen.

#include #include struct class {

int roll_no;char name[15];int m1, m2, m3;

} c[10];main( )

{int total, I;float avg;

for(I=O; I


If e1 is the object of an class employee. e1.update sal(); //illegal

It can only be called within input or display function. Void input(){ update sal();}

program-3Create the class item having the data members item_code,item_name,& price initialize these values using getdata function. Display only those item codes having price more than 100.

Class item{

private:int item_code;char item_name[20];int price;

public:void getdata(int x,int y[], int z){

item_code=x;strcpy(item_name,y);price=z;

}}item q[10];void main(){ int I,a,b,char.c[20];

for(i=0;i


1. Write a program to find length of the string without using strlen() function Ans. /* program to find length of string without string length function */

#include#includevoid main() { char *str; //declaring the string

cout >str;

// repeat the loop till Null character is foundfor (int len =0 ; *name!=\0;len++);

cout


cout


};//Member Function Definitionvoid rectangle :: area_peri( ){

int a, p;a = len * br;p = 2 * (len +br);cout


};void main()

{Time t1 , t2;t1.getTime();t2.getTime();cout


s3.display();s4.display();getch();

}7. Write program to calculate area of square and area of rectangle.Ans.

Void SquareArea(int s){

float area;area = s * s ;cout


num3 = num1 + num2;cout


cout >page;cout >price;

}

float calculate(){ return (price);}

void display(){ cout


e. Write a program to declare a class student containing data members roll number, name and percentage of marks. Read data for 2 students and display data of the student having higher percentage of marks.

Ans.Refer Q.No.

f. Explain difference between structure and class with exampleAns.Refer Q.No.

g. Find the errors from the following code.Rectify the codeClass Complex{

int real , imaginary;public :

void complex();void readdata();void showdata();

}

void main(){

complex c1;c1.ReadData();c1.DisplayData();

}Ans.Refer Q.No.

Summer 2008a. Define class with syntaxAns.Refer Q.No.

b. How many ways we can define member function in class? Give its syntax.Ans.Refer Q.No.

c. Declare a class simple interes having data member as pricniple amount rate of interest , number of year.The constructor will have default value of rate of interest as 11.5%.Accept this data for two object.Calcualte and display simple interest for each object

Ans.Refer Q.No.

d. Write a program to declare a class rectangle having data member length and breadth.Accept this data form one object and display area and perimeter of rectangle

Ans.Refer Q.No.

e. Write a program to declare class time having data member as hrs , min , sec. write a constructor to accept data and use display function for two object

Ans.Refer Q.No.

43


f. Describe memory allocation for objectAns.Refer Q.No.

Winter 2008a. Define inline function. Write its syntax. Give example.Ans.Refer Q.No.

b. Define friend function. Give example.Ans.Refer Q.No.

c. How to define a member function outside the body of class.Ans.Refer Q.No.

d. Comment on the following statement if display ( ) is a static member function of a class student, can it be called in the following way.

i. Student Sl ;ii. S1.display()

Ans.Refer Q.No.

e. Explain how friend function used to overload binary operatorAns.Refer Q.No.

f. Write a program to declare a class student consisting of data members Stud_name and Roll no. Write the member functions accept ( ) to accept and display ( ) to display the data for four students.

Ans.Refer Q.No.

g. Explain arrays of objects with exampleAns.Refer Q.No.

Summer 2009a. Define class and object. Give example.Ans.Refer Q.No.

b. Write syntax for defining member function outside the class definition.Ans.Refer Q.No.

c. Write program to calculate area of square and area of rectangle.Ans.Refer Q.No.

d. Write C++ program two read two numbers and find sum, duff., product and division using different member function for each.Ans.Refer Q.No.

e. Explain the concept object as function argumentAns.Refer Q.No.

44


Winter 2009a. When do we declare a member of a class static?Ans.Refer Q.No.

b. How is member function of a class defined?Ans.Refer Q.No.

c. Define class and object also give example.Ans.Refer Q.No.

d. Describe the mechanism of accessing data members and member functions in the . following cases.

(i) Inside main program(ii) Inside a member function of same class(iii) Inside a member function of another class.

Ans.Refer Q.No.

e. Describe memory allocation for objectsAns.Refer Q.No.

Summer 2010Define the term object. Ans.Refer Q.No.Ans.Refer Q.No. a. How to define member. Function outside body of class.Ans.Refer Q.No.

b. Write a program to declare a class Book having data-members as book-name, price and no. of pages. Accept this data for 2 objects and display name of book having greater price.

Ans.Refer Q.No.

c. Write output of following code. # include

Class Emp{ int eno;

char name [20];Float salary;

};Void main

{Emp e;

Cout < size of (Emp)


46

PrivateProtectedPublic

chapter 2 objects and classes

Documents