25. Virtual functions

// Shapes.h
class Shape {
public:
    Shape();
    virtual void draw();
};


class Circle : public Shape {
public:
    Circle( int radius );
    virtual void draw();
};


class Square : public Shape {
public:
    Square( int side );
    virtual void draw();
};

//main.cpp
#include "Shapes.h"

void push_shape( Shape* ps, int& cnt, Shape* shapes[] );

int main()
{
    // Array of pointers to shapes:
    Shape* shapes[ 100 ] = { 0 };

    int shape_cnt = 0;
    push_shape( new Circle(10), shape_cnt, shapes );
    push_shape( new Square(5), shape_cnt, shapes );

    for ( int idx = 0; idx < shape_cnt; ++idx ) {
        // Call virtual function:
        shapes[ idx ]->draw();
    }
}

void push_shape( Shape* ps, int& cnt, Shape* shapes[] )
{
    shapes[ cnt++ ] = ps;
}