using System;

namespace PolymorphismApplication

{

   abstract class Shape

   {

      public abstract int area();

   }

   class Rectangle:  Shape

   {

      private int length;

      private int width;

      public Rectangle( int a=0, int b=0)

      {

         length = a;

         width = b;

      }

      public override int area ()

      { 

         Console.WriteLine("Rectangle class area :");

         return (width * length); 

      }

   }

​

   class RectangleTester

   {

    public  static void Main(string[] args)

      {

         Rectangle r = new Rectangle(10, 7);

         double a = r.area();

         Console.WriteLine("Area: {0}",a);

         Console.ReadKey();

      }

   }

}