Polymorphism

 
using System;
public class Shape
{
    public int X { get; private set; }
    public int Y { get; private set; }
    public int Height { get; set; }
    public int Width { get; set; }

    // Virtual method
    public virtual void Draw()
    {
        Console.WriteLine("Performing base class drawing tasks");
    }
}

class Circle : Shape
{
    public override void Draw()
    {
        // Code to draw a circle...
        Console.WriteLine("Drawing a circle");
        base.Draw();
    }
}
class Rectangle : Shape
{
    public override void Draw()
    {
        // Code to draw a rectangle...
        Console.WriteLine("Drawing a rectangle");
        base.Draw();
    }
}
class Triangle : Shape
{
    public override void Draw()
    {
        // Code to draw a triangle...
        Console.WriteLine("Drawing a triangle");
        base.Draw();
    }
}

class Program
{
    static void Main(string[] args)
    {
        // Rectangle, Triangle and Circle can 
        // all be used whereever a Shape is expected. 
        System.Collections.Generic.List<Shape> shapes = 
             new System.Collections.Generic.List<Shape>();
        shapes.Add(new Rectangle());
        shapes.Add(new Triangle());
        shapes.Add(new Circle());

        //  Virtual method Draw is invoked on each of the derived classes, not the base class.
        foreach (Shape s in shapes)
        {
            s.Draw();
        }
    }

}