using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        //List<Book> lb = new List<Book>();

        //Author stephenKing = new Author("Stephen King", 900);

        //Book theStand = new Book("The Stand", "9375DKFH", stephenKing);

        //Console.WriteLine(theStand.Title);

        //stephenKing.WriteBook(theStand);

         Author stephen = new Author("Stephen King", 99);

        Author tolkien = new Author("J.R. Tolkien", 199);

        Author jkRowling = new Author("J.K. Rowling", 55);

        Book a = new Book("The Stand", "0-545-01022-5", stephen);

        Book b = new Book("Harry Potter", "1-745-01422-3", tolkien);

        Book c = new Book("Lord of the Rings", "9-741-21872-9", jkRowling);

        stephen.WriteBook(a);

        tolkien.WriteBook(b);

        jkRowling.WriteBook(c);

        Customer timmy = new Customer("Timmy", 12);

        timmy.BorrowBook(a);

        timmy.BorrowBook(b);

        timmy.BorrowBook(c);

        Console.WriteLine(string.Format("Customer {0} borrowed:",timmy.Name));

        foreach(Book book in timmy.Cart.Books)

        {

            Console.WriteLine(string.Format("    * Book {0} written by {1}.", book.Title, book.Writer.Name));

        }

    }

}

​

public class Person

{

    public string Name { get; set; }

    public int Age { get; set; }

    public Person(string name, int age)

    {

        Name = name;

        Age = age;

    }

}

​

public class Book

{

    public string Title { get; set; }

    public string ISBN { get; set; }

    public Author Writer { get; set; }

    public Book(string title, string isbn, Author writer)

    {

        Title = title;

        ISBN = isbn;

        Writer = writer;

    }

}

​

public class Author : Person

{

    public List<Book> BooksWritten { get; set; }

    public Author(string name, int age) : base(name, age)

    {

        BooksWritten = new List<Book>();

    }

    public void WriteBook(Book book)

    {

        BooksWritten.Add(book);

    {

        }

    }

}

public class LibraryCart    

{

​

    public List<Book> Books { get; set; }

    public LibraryCart()

    {

        Books = new List<Book>();

    }

    public void AddBook(Book book)

    {

        Books.Add(book);

    }

​

    public void RemveBook(Book book)

    {

        Books.Remove(book);

    }

}

​

public class Customer : Person

{

    public LibraryCart Cart { get; set; }

    public Customer(string name, int age) : base(name, age)

    {

        Cart = new LibraryCart();

    }

        public void BorrowBook(Book book)

        {

            Cart.AddBook(book);

        }

    }

​