C++ Program to illustrate an example of Pure Virtual functions

The word polymorphism means having many forms. Typically, polymorphism occurs when there is a hierarchy of classes and they are related by inheritance.

C++ polymorphism means that a call to a member function will cause a different function to be executed depending on the type of object that invokes the function.

Virtual Function : :

A virtual function is a function in a base class that is declared using the keyword virtual. Defining in a base class a virtual function, with another version in a derived class, signals to the compiler that we don’t want static linkage for this function.

Below is the source code for C++ Program to illustrate an example of Pure Virtual functions which is successfully compiled and run on Windows System to produce desired output as shown below :

SOURCE CODE : :

/*  C++ Program to illustrate an example of Pure Virtual functions */

#include<iostream>
 #include<graphics.h>
 #include<stdlib.h>
 using namespace std;


 /*************************************************************************///------------------------------  shape  --------------------------------///*************************************************************************/class shape
    {
       public:
        virtualvoid draw()=0;
    };

 /*************************************************************************///--------------------------  draw_rectangle  ---------------------------///*************************************************************************/class draw_rectangle:public shape
    {
       public:
        void draw()  { rectangle(225,225,180,180);  }
    };

 /*************************************************************************///---------------------------  draw_arc  --------------------------------///*************************************************************************/class draw_arc:public shape
    {
       public:
        void draw()  { arc(200,200,45,135,100);  }
    };

 /*************************************************************************///---------------------------  draw_circle  -----------------------------///*************************************************************************/class draw_circle:public shape
    {
       public:
        void draw()  { circle(200,200,60);  }
    };


 int main()
    {
       int driver=VGA;
       int mode=VGAHI;
       int error_code;

       initgraph(&driver,&mode,"..\\Bgi");

       error_code=graphresult( );

       if(error_code!=grOk)
          {
             restorecrtmode( );
             textmode(BW80);
             clrscr( );

             cout<<" \n Fatal Error  : Graphic Driver not initialized"<<endl;
             cout<<" Error Reason : "<<grapherrormsg(error_code)<<endl;
             cout<<" \n Press any key to exit...";

             getch( );
             exit(1);
          }

       shape *ptr;
       draw_rectangle r;
       draw_arc a;
       draw_circle c;

       ptr=&r;
       ptr->draw();

       ptr=&a;
       ptr->draw();

       ptr=&c;
       ptr->draw();

       getch();
       closegraph();
       return 0;
    }

Above is the source code and output for C++ Program to illustrate an example of Pure Virtual functions which is successfully compiled and run on Windows System to produce desired output.