class Shape {
public int width, height;
 public Shape(int x) {
    width = height = x;
    }
}

class Triangle : Shape {
 public string style;
  public Triangle(int x) : base(x) {
    style = "isosceles";
  }
}

public class MyBaseClass
{
    public MyBaseClass()
    {
        Console.WriteLine("MyBaseClass Parameterless");
    }

    public MyBaseClass(string message)
    {
        Console.WriteLine("MyBaseClass Message: " + message);
    }
}

public class MySubClass
{
    public MySubClass()
    {
        Console.WriteLine("MySubClass Parameterless");
    }

    public MySubClass(string message)
        : base(message)
    {
        Console.WriteLine("MySubClass Message: " + message);
    }

    public MySubClass(bool someUselessFlag)
        : this()
    {
        Console.WriteLine("MySubClass bool someUselessFlag constructor");
    }
}

var a = new MySubClass();
//outputs:
//MyBaseClass Parameterless
//MySubClass Parameterless

var b = new MySubClass("Hello World!");
//outputs:
//MyBaseClass Message: Hello World!
//MySubClass Message: Hello World!

var c = new MySubClass(true);
//outputs:
//MyBaseClass Parameterless
//MySubClass Parameterless
//MySubClass bool someUselessFlag constructor

public class Painter
{
    ...

    public void Draw(Shape shape)
    {
        //Drawing logic
    }

    ...
}

class Program
{
    ...

    //instantiates the Painter class so you can draw different shapes
    Painter painter = new Painter();

    //instantiates the Shape type that you want to draw
    Triangle triangle = new Triangle(15);

    //draws the triangle, which actually is a Shape type
    painter.Draw(triangle);

    ...
}