13-12.cpp

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#include<iostream.h>
const double PI=3.14159;
class shapes
{
protected:
   int x,y,r;
public:
   void insquare(int d,int w)
   {
     x=d;y=w;
    }
   void incircle(int r1)
   {
     r=r1;
   }
   virtual void show_area()=0;
};
class square:public shapes
{
public:
   void show_area()
   {
     cout<<"Area of square:"<<x*y;
     cout<<endl;
    }
};
class circle:public shapes
{
public:
	void show_area()
	{
		cout<<"Area of circle:"<<PI*r*r;
		cout<<endl;
	}
};
main()
{
  shapes *ptr[2];
  square s1;
  circle c1;
  ptr[0]=&s1;
  ptr[0]->insquare(20,5);
  ptr[0]->show_area();
  ptr[1]=&c1;
  ptr[1]->incircle(20);
  ptr[1]->show_area();
  return 0;
}