// polymorphism example
// abstract base class
#include<iostream.h>
#include<conio.h>
class cpolygon
{
protected:
int width,height;
public:
void setvalues (int a,int b)
{
width=a;
height=b;
}
virtual int area(void)=0;
};

class crectangle:public cpolygon
{
public:
 int area(void)
 {
  return(width*height);
 }
};
class ctriangle:public cpolygon
{
public:
int area(void)
{
return(width*height/2);
}
};
void main()
{
clrscr();
crectangle rect;
ctriangle trgl;
cpolygon *ppoly1=&rect;
cpolygon *ppoly2=&trgl;
ppoly1->setvalues (4,5);
ppoly2->setvalues (4,5);
cout<<ppoly1->area()<<endl;
cout<<ppoly2->area()<<endl;
getch();
}

/* 
----OUTPUT----
20
10
*/