// ejemplo miembros virtuales
#include <iostream.h>

class CPolygon {
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 << "area: " << area() << endl; }
};

class CRectangle: public CPolygon {
public:
    int area (void)
    { return (width * height); }
};

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

int main () {
  CRectangle rect;
  CTriangle trgl;
  CPolygon * ppoly1 = &rect;
  CPolygon * ppoly2 = &trgl;
  ppoly1->set_values (4,5);
  ppoly2->set_values (4,5);
  ppoly1->printarea();
  ppoly2->printarea();
  return 0;
}