using System;

public class Program

{

    public static void Main()

    {

        var rect = new Rectangle(3, 8); 

        var sq = new Square(8); 

        GrowWidthBy5AndOutputArea(rect); // should output 3 * 13 (39)

        GrowWidthBy5AndOutputArea(sq); // should output 8 * 13 (104) but ends up outputting 13 * 13 (169)

    }

    public static void GrowWidthBy5AndOutputArea(Rectangle r)

    {

        // method takes a rectangle, so it assumes rectangle rules apply

        // rectangles allow you to change just the width

        r.Width += 5;

        Console.WriteLine("The area is now {0}", r.GetArea());

    }

}

​

​

public class Rectangle

{

    public virtual int Length { get; set; }

    public virtual int Width { get; set; }

    public Rectangle(int length, int width)

    {

        Length = length;

        Width = width;

    }

    public int GetArea()

    {

        return Length * Width;  

    }

}

​

// this square implementation assumes that length and width

// are always the same, so we override the set method to keep

// them in sync

public class Square : Rectangle

{

    private int _length;

    public override int Length

    {

        get { return _length; }

        set 

        { 

            _length = value;

            _width = value;

        }

    }

    private int _width;

    public override int Width

    {

        get { return _width; }

        set 

        {

            _width = value;

            _length = value;

        }

    }

    public Square(int width) 

        : base(width, width)

    {

    }

}

​

​