c++ program example of inheritance and virtual function

#include < stdio.h>
#include < iostream.h>
#include < stdlib.h>


// Prototype graphics library function to draw a circle

void glib_draw_circle (int x, int y, int radius);



// Shape base class declaration

class Shape

{

protected:

int m_x; // X coordinate

int m_y; // Y coordinate



public:

// Pure virtual function for drawing

virtual void Draw() = 0;



// A regular virtual function

virtual void MoveTo(int newX, int newY);



// Regular method, not overridable.

void Erase();



// Constructor for Shape

Shape(int x, int y);



// Virtual destructor for Shape

virtual ~Shape();

};



// Circle class declaration

class Circle : public Shape

{

private:

int m_radius; // Radius of the circle



public:

// Override to draw a circle

virtual void Draw();



// Constructor for Circle

Circle(int x, int y, int radius);



// Destructor for Circle

virtual ~Circle();

};



// Shape constructor implementation

Shape::Shape(int x, int y)

{

m_x = x;

m_y = y;

}



// Shape destructor implementation

Shape::~Shape()

{

//...

}



// Circle constructor implementation

Circle::Circle(int x, int y, int radius) : Shape (x, y)

{

m_radius = radius;

}



// Circle destructor implementation

Circle::~Circle()

{

//...

}



// Circle override of the pure virtual Draw method.

void Circle::Draw()

{

glib_draw_circle(m_x, m_y, m_radius);

}



void main()

{

// Define a circle with a center at (50,100) and a radius of 25

Shape *pShape = new Circle(50, 100, 25);



// Define a circle with a center at (5,5) and a radius of 2

Circle aCircle(5,5, 2);



// Various operations on a Circle via a Shape pointer

pShape->Draw();

pShape->MoveTo(100, 100);

pShape->Erase();

delete pShape;



// Invoking the Draw method directly

aCircle.Draw();

}