namespace persianedito
{
    class sezaralgorithm
    {
public int upreToint(char ch)
        {
            return ch - 65;
        }

public int lowerToint(char ch)
        {
            return ch - 97;
        }

public int intToUper(int value)
        {
            return (char)(value+65);
        }

public int intTolower(int value)
        {
            return (char)(value+97);
        }

public bool islower(char ch)
        {
            if (ch >= 97 && ch <= 122)
            {
                return true;
            }
            else
            {
                return false;
            }
        }

public bool isUper(char ch)
        {
            if (ch >= 65 && ch <= 90)
            {
                return true;
            }
            else
            {
                return false;
            }
        }

public string encryption(string textToencryption, char key)
        {
            char[] plaintext = textToencryption.ToCharArray();
            char[] cipher = new char[textToencryption.Length];
        
        }

for (int i = 0; i < textToencryption.Length; i++)
   {
        if (islower(plaintext[i]) == true)
        {
         ciphertext[i] = intTolower((lowerToint(plaintext[i]) + upreToint(key)) % 26);
         } 

if (isUper(plaintext[i]) == true)
    {
      ciphertext[i] = intToUper((upreToint(plaintext[i]) + upreToint(key)) % 26);
     }

            string cipher = "";
            for (int i = 0; i < textToencryption.Length; i++)
            {
                cipher += ciphertext[i].ToString(); 
            }

public string decription(string textTodecription, char key)
    {
        string plain = "";
        char[] plaintext = new char[textTodecription.Length];
        char[] ciphertext = textTodecription.ToCharArray();
            
        for (int i = 0; i < textTodecription.Length; i++)
         {
            if (islower(ciphertext[i]) == true)
            {
             plaintext[i] = intTolower((lowerToint(ciphertext[i]) + upreToint(key)) % 26);
            }
            if (isUper(plaintext[i]) == true)
            {
               plaintext[i] = intToUper((upreToint(ciphertext[i]) + upreToint(key)) % 26);
            }  
          }
            
          for (int i = 0; i < textTodecription.Length; i++)
          {
                plain += plaintext[i].ToString();
                return plain;
          }
        }

private void btnencripttext_Click(object sender, EventArgs e)
        {
            sezaralgorithm sezar = new sezaralgorithm();
            txtcipher.Text = sezar.encription(txtplain.Text, Convert.ToChar(cmbKey.Text));
        }

private void btnplainbrows_Click(object sender, EventArgs e)
        {
            if (openFileDialog1.ShowDialog() == DialogResult.ok)
            {
                txtplainfilename.Text = openFileDialog1.FileName;
            }
        }

namespace persianedito
{
    public partial class frmencription : Form
    {

        string plaintext = "";
        string ciphertext = "";
در گام بعدی متن را از فایل انتخاب شده میخوانیم و در متغییر plaintext قرار میدهیم.
private void btnplainbrows_Click(object sender, EventArgs e)
        {
            string plaintext = "", ciphertext = "";
            if (openFileDialog1.ShowDialog() == DialogResult.ok)
            {
                txtplainfilename.Text = openFileDialog1.FileName;
                plaintext = System.IO.File.ReadAllText(txtplainfilename.Text);
            }
        }

private void btnplainbrows_Click(object sender, EventArgs e)
        {
            string plaintext = "", ciphertext = "";
            sezaralgorithm sezar = new sezaralgorithm();
            if (openFileDialog1.ShowDialog() == DialogResult.ok)
            {
                txtplainfilename.Text = openFileDialog1.FileName;
                plaintext = System.IO.File.ReadAllText(txtplainfilename.Text);
                ciphertext = sezar.encription(plaintext, Convert.ToChar(cmbfilekey));
            }
        }

private void btncipherbrows_Click(object sender, EventArgs e)
        {
            
            if (saveFileDialog1.ShowDialog() == DialogResult.OK)
            {
                txtcipherfilename.Text = saveFileDialog1.FileName;
                System.IO.File.WriteAllText(saveFileDialog1.FileName,ciphertext);
              
            }
        }

private void btncipttext_Click(object sender, EventArgs e)
        {
            sezaralgorithm sezar = new sezaralgorithm();
            txtplain.Text = sezar.decription(txtcipher.Text, Convert.ToChar(cmbKey.Text));
           
        }