using System.Collections.Generic;
using System.Linq;
using System;

public static class Program
{
    public static void Main()
    {
        var dogs = new List<Dog>();
        dogs.Add(new Dalmatier());
        dogs.Add(new Terrier());

        foreach (var dog in dogs)
        {
            dog.Bark();
		}

		Console.WriteLine("");
		foreach(var dog in dogs)
		{
            dog.AngryBark();
		}

		Console.WriteLine("");
		foreach(var dog in dogs)
		{
            dog.Sleep();
        }

		Console.WriteLine("");
		foreach(var dog in dogs.OfType<Dalmatier>())
		{
			dog.Sleep();
		}
    }
}

public abstract class Dog
{
    /// <summary>
    /// Every dog Barks in a different way, abstract forces an implementation
    /// </summary>
    public abstract void Bark();

    /// <summary>
    /// Default dogs do the same bark just twice in a row when they are angry
    /// </summary>
    public virtual void AngryBark()
    {
        Bark();
        Bark();
    }

    /// <summary>
    /// All dogs have the same sleep sound, no virtual or abstract necessary.
    /// </summary>
    public void Sleep()
    {
        System.Console.WriteLine("Zzzzzzzz");
    }
}

public class Dalmatier : Dog
{
    public override void Bark()
    {
        System.Console.WriteLine("Waf");
    }

    /// <summary>
    /// A Dalmatier makes a really weird sleep sound
    /// </summary>
    public new void Sleep()
    {
        System.Console.WriteLine("Grrnnnnrzzzz");
    }
}

public class Terrier : Dog
{
    public override void Bark()
    {
        System.Console.WriteLine("WOEF");
    }

    /// <summary>
    /// An angry Terrier has a special bark
    /// </summary>
    public override void AngryBark()
    {
        System.Console.WriteLine("GRRRRRR WAF");
        System.Console.WriteLine("GRRRRRR WAF WAF");
    }
}