using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        var num = new Number();

        num.numberChanged +=(o,n) =>{ // o stands for old value and n stands for new value

            Console.WriteLine("Value was changed from {0} to {1}",o,n);

        };

        num.Value=10; // this will let the numberChanged event to be fired

        num.Value=100;

    }

}

​

// this delegate was created to be used in passing the old and new value during event firing

public delegate void NumberChangedEvent(int oldValue,int newValue);

​

public class Number{

    public event NumberChangedEvent numberChanged;

    private int _value=0;

    public int Value

    {

        get

        {

            return _value;

        }

        set

        {

            if(value!=_value)

            {

                int oldValue=_value; // store the value in order to pass it in the event

                _value=value;

                if(numberChanged!=null)

                    numberChanged(oldValue,_value);

            }

        }

    }

}