// virtual members
#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 ()
    {

        return 0;

    }

};

class Rectangle: public Polygon
{

public:

    int area ()
    {
        return width * height;

    }

};

class Triangle: public Polygon {

public:

    int area ()
    {
        return (width * height / 2);
    }

};

int main ()
{
    Rectangle rect;

    Triangle trgl;

    Polygon poly;

    Polygon * ppoly1 = &rect;

    Polygon * ppoly2 = &trgl;

    Polygon * ppoly3 = &poly;

    ppoly1->set_values (4,5);

    ppoly2->set_values (4,5);

    ppoly3->set_values (4,5);

    cout << ppoly1->area() << endl;

    cout << ppoly2->area() << endl;

    cout << ppoly3->area() << endl;

    return 0;
}