C# delegates are similar to pointers to functions, in C or C++. The delegates are used to perform tasks associated with a function while that function is invoked delegate will perform the task.

For example, Lets take a delegate:

public delegate int the firstDelegate (string s);

The preceding delegate can be used to invoke when any function with int return type and string parameter is invoked

Syntax for delegate declaration is:

delegate <return type> <delegate-name> <parameter list>

Implementing a Delegate :

using System;

delegate int NumberChanger(int n);
namespace DelegateAppl
{
   class TestDelegate
   {
      static int num = 10;
      public static int AddNum(int p)
      {
         num += p;
         return num;
      }

      public static int MultNum(int q)
      {
         num *= q;
         return num;
      }
      public static int getNum()
      {
         return num;
      }

      static void Main(string[] args)
      {
         //create delegate instances
         NumberChanger nc1 = new NumberChanger(AddNum);
         NumberChanger nc2 = new NumberChanger(MultNum);

         //calling the methods using the delegate objects
         nc1(25);
         Console.WriteLine("Value of Num: {0}", getNum());
         nc2(5);
         Console.WriteLine("Value of Num: {0}", getNum());
         Console.ReadKey();
      }
   }
}

This delegates are called single cast delegates

Multicast Delegate

Multicasting of a Delegate

Delegate objects can be composed using the "+" operator. It shows the binding of the function with the delegate. Composed delegate calls two delegates from which it was composed. To remove a component delegate from a composed delegate "-" operator is used in multicast delegate.

using System;

delegate int NumberChanger(int n);
namespace DelegateAppl
{
   class TestDelegate
   {
      static int num = 10;
      public static int AddNum(int p)
      {
         num += p;
         return num;
      }

      public static int MultNum(int q)
      {
         num *= q;
         return num;
      }

      public static int getNum()
      {
         return num;
      }

      static void Main(string[] args)
      {
         //create delegate instances
         NumberChanger nc;
         NumberChanger nc1 = new NumberChanger(AddNum);
         NumberChanger nc2 = new NumberChanger(MultNum);
         nc = nc1;
         nc += nc2;

         //calling multicast
         nc(5);
         Console.WriteLine("Value of Num: {0}", getNum());
         Console.ReadKey();
      }
   }
}