Caesar Cipher encryption application full code below

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

namespace encryptionsystem
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string origMessage = normalText.Text;
            int shiftNum = Int32.Parse(textBox3.Text);
            cypherText.Text = doEncryption(origMessage.ToLower(), shiftNum);
        }

        private static string doEncryption(string words, int shiftNo)
        {
            
            
            char[] buffer = words.ToCharArray();

            for (int i = 0; i < buffer.Length; i++) { // each letter will be seperated and then changed. char letter = buffer[i]; // shift the letters according to the shift no variable letter = (char)(letter + shiftNo); // Subtract 26 on overflow. // Add 26 on underflow. if (letter > 'z')
                {
                    letter = (char)(letter - 26);
                }
                else if (letter < 'a')
                {
                    letter = (char)(letter + 26);
                }
                // Store.

                buffer[i] = letter;
            }

            return new string(buffer);
        }

        private void helpToolStripMenuItem_Click(object sender, EventArgs e)
        {
            helpScreen helpForm = new helpScreen();

            helpForm.Show();
        }

        
    }
}