// A Hello World! program in C#.
using System;
namespace HelloWorld
{
    class Hello 
    {
        static void Main() 
        {
            Console.WriteLine("Hello World!");
            
            // Keep the console window open in debug mode.
            Console.WriteLine("Press any key to exit.");
            Console.ReadKey();
        }
    }
    
    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 Test
    {
        // Print the title of the book.
        static void PrintTitle(Book b)
        {
            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:
            Console.WriteLine("Paperback Book Titles:");
            // Create a new delegate object associated with the static 
            // method Test.PrintTitle:
            bookDB.ProcessPaperbackBooks(new ProcessBookDelegate(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(new ProcessBookDelegate(totaller.AddBookToTotal));
            Console.WriteLine("Average Paperback Book Price: ${0:#.##}",
                              totaller.AveragePrice());
        }
        
        // Initialize the book database with some test books:
        static void AddBooks(BookDB bookDB)
        {
            bookDB.AddBook("The C Programming Language", 
                           "Brian W. Kernighan and Dennis M. Ritchie", 19.95m, true);
            bookDB.AddBook("The Unicode Standard 2.0", 
                           "The Unicode Consortium", 39.95m, true);
            bookDB.AddBook("The MS-DOS Encyclopedia", 
                           "Ray Duncan", 129.95m, false);
            bookDB.AddBook("Dogbert's Clues for the Clueless", 
                           "Scott Adams", 12.00m, true);
        }
    }
}