// dynamic allocation and polymorphism

#include <iostream>
using namespace std;

class Polygon {
  protected:
    int width, height;
  public:
    void set_values (int a, int b)
      { width=a; height=b; }
    virtual int area (void) =0;
    void printarea (void)
      { cout << "The area is " << this->area() << endl; }
  };

class Rectangle: public Polygon {
  public:
    int area (void)
      { return (width * height); }
  };

class Triangle: public Polygon {
  public:
    int area (void)
      { return (width * height / 2); }
  };

int main () {
  Polygon *poly1 = new Rectangle;
  Polygon *poly2 = new Triangle;
  poly1->set_values (4,5);
  poly2->set_values (4,5);
  poly1->printarea();
  poly2->printarea();
  delete poly1;
  delete poly2;
  getchar();
  return 0;
}