// A set of classes for handling a bookstore:
namespace Bookstore
{
    using System.Collections;// Describes a book in the book list:
    public struct Book
    {
        public string Title;        // Title of the book.
        public string Author;       // Author of the book.
        public decimal Price;       // Price of the book.
        public bool Paperback;      // Is it paperback?

        public Book(string title, string author, decimal price, bool paperBack)
        {
            Title = title;
            Author = author;
            Price = price;
            Paperback = paperBack;
        }
    }// Declare a delegate type for processing a book:
    public delegate void ProcessBookDelegate(Book book);// Maintains a book database.
    public class BookDB
    {
        // List of all books in the database:
        ArrayList list = new ArrayList();// Add a book to the database:
        public void AddBook(string title, string author, decimal price, bool paperBack)
        {
            list.Add(new Book(title, author, price, paperBack));
        }// Call a passed-in delegate on each paperback book to process it: 
        public void ProcessPaperbackBooks(ProcessBookDelegate processBook)
        {
            foreach (Book b in list)
            {
                if (b.Paperback)
                    // Calling the delegate:
                    processBook(b);
            }
        }
    }
}// Using the Bookstore classes:
namespace BookTestClient
{
    using Bookstore;// Class to total and average prices of books:
    class PriceTotaller
    {
        int countBooks = 0;
        decimal priceBooks = 0.0m;internal void AddBookToTotal(Book book)
        {
            countBooks += 1;
            priceBooks += book.Price;
        }internal decimal AveragePrice()
        {
            return priceBooks / countBooks;
        }
    }// Class to test the book database:
    class TestBookDB
    {
        // Print the title of the book.
        static void PrintTitle(Book b)
        {
            System.Console.WriteLine("   {0}", b.Title);
        }// Execution starts here.
        static void Main()
        {
            BookDB bookDB = new BookDB();// Initialize the database with some books:
            AddBooks(bookDB);// Print all the titles of paperbacks:
            System.Console.WriteLine("Paperback Book Titles:");// Create a new delegate object associated with the static 
            // method Test.PrintTitle:
            bookDB.ProcessPaperbackBooks(PrintTitle);// Get the average price of a paperback by using
            // a PriceTotaller object:
            PriceTotaller totaller = new PriceTotaller();// Create a new delegate object associated with the nonstatic 
            // method AddBookToTotal on the object totaller:
            bookDB.ProcessPaperbackBooks(totaller.AddBookToTotal);

            System.Console.WriteLine(