Creating the classes

Lets start by creating a C# console app and clearing out all of the existing template code. Next, we type the first line of our code:

using static System.Console; 

As usual, we need this so that we can use WriteLine. Next, create an abstract class to work with. For this, type the following:

abstract class Shape 
{ 
} 

This class here is needed so that we can switch between objects of the type Shape. People sometimes do something similar with interfaces. Well, I'm using an abstract class for the following reason: classes are used to essentially express the "is a" type of relationship, while interfaces are used to express the "can be used as" type of relationship. Let's take a look and see why I chose to go with a class. Underneath the closing brace of our Shape class, start a new line and type the following:

class Rectangle:Shape...