polymorphism_1.cs

    using System;
    using System.Collections.Generic;
    
    public class Shape
    {
        // A few example members
        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)
        {
            // Polymorphism at work #1: a Rectangle, Triangle and Circle
            // can all be used whereever a Shape is expected. No cast is
            // required because an implicit conversion exists from a derived 
            // class to its base class.
            var shapes = new List<Shape>
            {
                new Rectangle(),
                new Triangle(),
                new Circle()
            };

            // Polymorphism at work #2: the virtual method Draw is
            // invoked on each of the derived classes, not the base class.
            foreach (var shape in shapes)
            {
                shape.Draw();
            }

            // Keep the console open in debug mode.
            Console.WriteLine("Press any key to exit.");
            Console.ReadKey();
        }

    }

    /* Output:
        Drawing a rectangle
        Performing base class drawing tasks
        Drawing a triangle
        Performing base class drawing tasks
        Drawing a circle
        Performing base class drawing tasks
     */