Virtual function

Programming fundamental
Submitted by : Sidra Tahir
Submitted to : Ma'am Shumaila
Subject : object oriented program
Roll no : 165
Class : BSCS
Date : 30- 03-2020
Session : 2019-2023
COVT. POST GRADUATE COLLEGE FOR WOMENS GULBERG LAHORE

CONTENTS
 Polymorphism
 Virtual function
 Pointer to all object
 Abstractconcrete class
 Pure virtual class
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Polymorphism
In object-oriented
programming, polymorphism ref
ers to a programming language's
ability to process objects
differently depending on their
data type or class. More
specifically, it is the ability to
redefine methods for derived
classes.

Real life Example
 A person at the same time can have different characteristic.
Like a man at the same time is a father, a husband, an
employee. So the same person posses different behavior in
different situations. This is called polymorphism.
you have a smartphone for communication. The
communication mode you choose could be anything. It can be
a call, a text message, a picture message, mail, etc. So, the goal
is common that is communication, but their approach is
different.

Example Of Polymorphism
#include<iostream.h>
#include<conio.h>
class test
{
clrscr();
private:
int n;
public:
void in()
{
cout<<"enter a number:";
cin>>n;
}
Continue……………………

void out()
{
cout<<"the value of n = "<<n;
}
};
void main()
{
clrscr();
test*ptr;
ptr=new test;
ptr->in();
ptr->out();
getch();
}

Output and working of program
output
Working:
The above program declares a class test and a pointer ptr of type test. The pointer can
refer to object of the class. The new operator creates an object in the memory and stores
the address in ptr. The program then uses the pointer to call the member function of the
object being referenced by the pointer. The symbol -> is used to access the member of any
object through pointer. The use of dot operator with pointer to access any member is
invalid.

 Virtual means existing in effect but not really.
 A type of function in some part of a program but does not exist really is
called virtual function.
 A virtual function is defined in the present class and can be overridden in
child classes.
Virtual function

Class class-name
{
Public:
Virtual void member- function-name()
{
…………. …………... body of base class
}
};
Syntax of virtual function
keyword

#include<conio.h>
class cbaseclass
{
public:
virtual void sayhello()
{
cout<<"hello from the cbaseclassnn";
}
void sayhi()
{
cout<<" hi from cbaseclassnn";
}
Example

program
#include<conio.h>
class a
{
public:
void disp()
{
cout<<" n i am from base class a";
}
};
class b : public a
{
public:
void disp()
{
cout<<"n i am from base class b";
}
};
continue……….

class c: public b
{
public:
void disp()
{
cout<<"n i am from base class c";
}
};
void main()
{
a *pa;
b objb;
c objc;
pa=&objb;
pa->disp();
pa=&objc;
pa->disp();
getch();
}

Output of program
output
i am from base class a
i am from base class a

Working of program
The program declares three class a are the parent class and b and c are the child
classes. Each class has a member function disp().The disp() function in parent class a is
declared as virtual function. The child classes b and c override that member function.
The program declares one object of each class. It also declares a pointer ptr of class a.
the address of each object is stored in pointer and disp(0 function is called . Each time
the disp() function is called, corresponding function execution is executed

A type of virtual function that has no body is known as pure virtual
function. A function can be declared as pure virtual function by adding
two things:
 The keyword virtual at the start of the function declarator.
 The =0 at the end of function declaratory.
Note: the pure virtual function are used in the classes which are not
used directly. The user can inherit the class and then override the pure
virtual function in the child class.
Pure virtual function

Class class-name
{
Public:
Virtual return-type function-name()=0
};
syntax
keyword
=0 indicate
that function
is pure
virtual
function

#include<conio.h>
Class A
{
clrscr();
Public:
Virtual void disp()=0;
};
Class B : public A
{
void disp()
{
Cout <<“n I am form derived class B”;
}};
Program and Example
Class C :public B
{
Public:
Void disp()
{
Cout<<“n I am form derived class
C”;
}
};
Int main()
{
B obj b;
C obj c;
Obj b.disp)();
Obj c.disp();
getch();
}
};

Output and working of program
Output
Working:
The program declares three class A are the parent class and B and C are
the child classes. Each class has a member function disp().The disp()
function in parent class A is declared as pure virtual function. The child
classes b and c override that member function.
The program declares one object of each class and disp(0 function is called
. Each time the disp() function is called, corresponding function execution
is executed

Abstract class
By definition, an abstract class in C++ is a class that has at
least one pure virtual function (i.e., a function that has no
definition).

Syntax
abstract Class < class-name>
{
Public:
Abstract void function-name()
{
……….
}
Abstract method
}
keyword

Program and Example
#include<conio.h>
Class abstract interface
{
Public:
Virtual void numbers()=0;
Void input();
Int a,b;
};
Void abstract interface : : input
{
Cout<<“enter the two numbers”;
Cin>>a>>b;
}
Continue………………..

Class add: public abstract interface
{
Public:
Void numbers()
{
Int sum,a,b;
Sum=a+b;
Cout<<“sum is << sum<<“n”;
}
};
Class sub: public abstract interface
{
Public:
Void numbers()
{
Cout<<“diff is << diff <<“n”;
}
};
int main()
{
Output
Add obj1;
Obj1 input();
Obj1 numbers();
Sub obj2;
Obj2 input();
Obj2 numbers();
}
output

Working of program
The program declares parent as abstract class interface and the child classes
are add and subclass. The child class add override the pure virtual function
declared in parent class. It is important to declare a pure virtual function in
parent class and override it in all child classes to implement polymorphism.
Takin g input in both child classes and then in main function made objects of
both child classes as input and numbers.

Abstract class concrete class
• Concrete classes are not
interface.
• Concrete classes can be base or
derived.
• Pure virtual function are may
not present in concrete
class.these classes can
instantiate the objects.
• Abstract classes are the
interface
• Abstract class is generally a base
class.
• Pure virtual function should be
present in the abstract class.
• This classes cannot instantiate
the facts.
Shape
2D shape 3D SHAPE
SQAURE
CIRCLE TRIANGLE
CUBE SPHERE
CYLINDER
ABSTACT
CLASSES
CONCRETE
CLASSES

Pointer to call objects
 When accessing members of a class given a pointer to an object, use the arrow (-
>) operator instead of dot (.) operator.
 Must initialize the pointer before using it.
 Pointer athematic is relative to the base type of the pointer.

syntax
ptr -> member
It is the name of pointer that reference an object.
It is the member access operator that is used to access a member of
object.
It is the class member to be accessed.

Program
#incl;ude<conio.h>
Class laptop
{
Int ram;
Public:
Int usb;
Void getdata (int a)
{
Ram =a;
}
Void disp()
{
Cout<<“ram : ” << ram<< endl;
Cout<<“usb : ”<< usb < <endl;
} };
ntI main()
{
Laptop dell
Laptop *pdell = &dell;
Pdell -> usb = 3;
Pdell->getdata(20);
Pdell-> disp()
Getch();
}
Output

Working of program
The program declares a class laptop and a pointer pdell of type laptop. The pointer
refer the object of the class. The new operator creates an object in the memory and
stores the address in pdell. The program then uses the pointer to call the member
function of the object being referenced by the pointer. The symbol -> is used to access
the member of any object through pointer.

Virtual function

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