using System;

// create the abstract class

public abstract class Animal

{

    public string Name {get;set;}

    public int Age {get;set;}

    public bool Female {get;set;}

}

​

// create the interface

internal interface Pet

{

    string Playful

    {get;set;}

}

​

​

// create the derived classes

public class Cat : Animal, Pet

{

    public string Breed {get;set;}

    public string Playful {get;set;}

    public new void ToString()

    {

        Console.WriteLine("Cat: a kitty is here.");

    }

}

​

public class Fish : Animal, Pet

{

    public int SwimSpeed;

    public string Playful{get;set;}

    public new void ToString()

    {

        Console.WriteLine("Fish: Smells fishy.");

    }

}

​

// create the zoo class

public class Zoo 

{

    public string Name {get;set;}

    public string City {get;set;}

    public int Capacity {get;set;}

    // list

    System.Collections.Generic.List<Animal> Animals = new System.Collections.Generic.List<Animal>();

    // constructor for class Zoo

    public void zoo(string a, string b, int c)

    {

        Name = a;

        City = b;

        Capacity = c;

    }

    public void addAnimal(Animal a)

    {

        Animals.Add(a);

    }

    public void removeAnimal(Animal a)

    {

        Animals.Remove(a);

    }

    public void printMembers()

    {

        foreach (Animal member in Animals)

        {

            Console.WriteLine(member);

        }

    }

} 

​

// test

public class Program 

{

    public static void Main(string[] args) 

    {

        //create a zoo

        Zoo NationalZoo= new Zoo();

        NationalZoo.zoo("Smithsonian's National Zoo","Washington D.C.",5000);

        Console.WriteLine("Welcome to the {0},it located at {1} and has capacity of {2}.",NationalZoo.Name,NationalZoo.City,NationalZoo.Capacity);

        Console.WriteLine("----------------------------------------------------------------");

        // create two test animal

        Cat C1 = new Cat();

        C1.ToString();

        Fish F1 = new Fish();

        F1.ToString();

        Console.WriteLine("----------------------------------------------------------------");

        // add all test animals

        NationalZoo.addAnimal(C1);

        NationalZoo.addAnimal(F1);

        NationalZoo.printMembers();

        Console.WriteLine("The above two animal have been added");

        Console.WriteLine("----------------------------------------------------------------");

        // remove test cat from animals

        NationalZoo.removeAnimal(C1);

        Console.WriteLine("The Cat has been removed from the list, now only the animal below still in the list:");

        NationalZoo.printMembers();

        Console.WriteLine("----------------------------------------------------------------");

    }

}

​

​