using System;

// Define a custom delegate that has a string parameter and returns void.
delegate void CustomDel(string s);

class TestClass
{
  // Define two methods that have the same signature as CustomDel.
  static void Hello(string s)
  {
    System.Console.WriteLine(" Hello, {0}!", s);
  }

  static void Goodbye(string s)
  {
    System.Console.WriteLine(" Goodbye, {0}!", s);
  }

  static void Main()
  {
    // Declare instances of the custom delegate.
    CustomDel hiDel, byeDel, multiDel, multiMinusHiDel;

    // In this example, you can omit the custom delegate if you 
    // want to and use Action<string> instead.
    //Action<string> hiDel, byeDel, multiDel, multiMinusHiDel;

    // Create the delegate object hiDel that references the
    // method Hello.
    hiDel = Hello;

    // Create the delegate object byeDel that references the
    // method Goodbye.
    byeDel = Goodbye;

    // The two delegates, hiDel and byeDel, are combined to 
    // form multiDel. 
    multiDel = hiDel + byeDel;

    // Remove hiDel from the multicast delegate, leaving byeDel,
    // which calls only the method Goodbye.
    multiMinusHiDel = multiDel - hiDel;

    Console.WriteLine("Invoking delegate hiDel:");
    hiDel("A");
    Console.WriteLine("Invoking delegate byeDel:");
    byeDel("B");
    Console.WriteLine("Invoking delegate multiDel:");
    multiDel("C");
    Console.WriteLine("Invoking delegate multiMinusHiDel:");
    multiMinusHiDel("D");
  }
}

Invoking delegate hiDel:
 Hello, A!
Invoking delegate byeDel:
 Goodbye, B!
Invoking delegate multiDel:
 Hello, C!
 Goodbye, C!
Invoking delegate multiMinusHiDel:
 Goodbye, D!

 // Declare a delegate.
delegate void Del(string str);

// Declare a method with the same signature as the delegate.
static void Notify(string name)
{
  Console.WriteLine("Notification received for: {0}", name);
}


 // Create an instance of the delegate.
Del del1 = new Del(Notify);

// C# 2.0 provides a simpler way to declare an instance of Del.
Del del2 = Notify;

// Instantiate Del by using an anonymous method.
Del del3 = delegate(string name)
  { Console.WriteLine("Notification received for: {0}", name); };

// Instantiate Del by using a lambda expression.
Del del4 = name => { Console.WriteLine("Notification received for: {0}", name); };

// 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("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);
    }
  }
}

Paperback Book Titles:
  The C Programming Language
  The Unicode Standard 2.0
  Dogbert's Clues for the Clueless
Average Paperback Book Price: $23.97

public delegate void ProcessBookDelegate(Book book);

bookDB.ProcessPaperbackBooks(PrintTitle);

bookDB.ProcessPaperbackBooks(totaller.AddBookToTotal);

processBook(b);