Windows form application in Visual Studio to convert a string to uppercase and lowercase

Code:

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 UpperCaseAndLowerCase

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        private void Form1_Load(object sender, EventArgs e)

        {

        }

        private void button1_Click(object sender, EventArgs e)

        {

            string a=richTextBox1.Text;

            richTextBox2.Text = a.ToUpper();

            richTextBox3.Text = a.ToLower();

        }

        private void label1_Click(object sender, EventArgs e)

        {

           

        }

        private void button2_Click(object sender, EventArgs e)

        {

            MessageBox.Show("Click OK to exit from window");

            // this.Close();

            Application.Exit();

        }

    }

}

Output: