Events and Delegates in C#

MainClass

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace EventsAndDelegates
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        /*
         Events are used to Get notify when a specific task is completed. Then we can call our functions. 
         Due to events, we are never required to edit our class which contains a specific code
        */

        private void Form1_Load(object sender, EventArgs e)
        {
            // Create Object of a class
            Calculator mCalculator = new Calculator();

            // Adding a subscriber
            /*
             * All the method we add to this event will be triggered when the function 'AddNum' execution is completed
             * For this example we want to trigger SendEmail and SendMessage. So these methods will be triggered
             * If we do not use events and delegates, then we need to add these methods AddNum function to Calculator class
             * Which could cause some problems. So this is the bes way
             */
            mCalculator.NumberAdded += SendEmail;
            mCalculator.NumberAdded += SendMessage;

            // Call AddNum function in Calculator class
            mCalculator.AddNum(5, 10);
        }

        // Method to send email
        private void SendEmail(int result) {
            MessageBox.Show(String.Format("Result is: {0}. Sending Email", result));
        }

        // Method to send messaage
        private void SendMessage(int result)
        {
            MessageBox.Show(String.Format("Result is: {0}. Sending Message", result));
        }
    }
}

Calculator

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EventsAndDelegates
{
    class Calculator
    {
        // Create a delegate with one parameter 'result'
        public delegate void CalculatorEventHandler(int result);
        // Create an event for that delegate
        public event CalculatorEventHandler NumberAdded;


        // Write a function to add two numbers
        public void AddNum(int num1, int num2)
        {
            int result = num1 + num2;
            // After addition, call OnResult
            OnResult(result);
        }

        protected virtual void OnResult(int result)
        {
            // This methods checks, if there are any subscribers for this events
            // If true, it fires event and all methods subscribed to this event gets executed
            if (NumberAdded != null)
                NumberAdded(result);
        }
    }
}