[C/C++] virtual

#include <stdio.h>

class CPolygon
{
public:
    void set_values(int a, int b)
    {
        width = a;
        height = b;
    }

    virtual int area()
    {
        return 0;
    }

    void name()
    {
        printf("CPolygon\n");
    }

protected:
    int width;
    int height;
};

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

    void name()
    {
        printf("CRectangle\n");
    }
};

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

    void name()
    {
        printf("CTriangle\n");
    }
};

int main()
{
    CPolygon poly;
    CRectangle rect;
    CTriangle trgl;

    CPolygon * p1 = &poly;
    CPolygon * p2 = &rect;
    CPolygon * p3 = &trgl;

    p1->set_values(4, 5);
    p2->set_values(4, 5);
    p3->set_values(4, 5);

    printf("p1: %d\n", p1->area()); //0
    printf("p2: %d\n", p2->area()); //20
    printf("p3: %d\n", p3->area()); //10

    //CRectangle * p4 = &poly;
    CRectangle * p5 = &rect;
    //CRectangle * p6 = &trgl;

    p1->name(); //CPolygon
    p2->name(); //CPolygon
    p3->name(); //CPolygon

    return 0;
}