Affichage dans un richtextBox

        
private void chaine(long l)
        {
             string s="" ;
             while (l >= 27) ;
             {
                 s = s + (char)((byte)(l %27)+96);
               rtb.AppendText(s);             
}        
}

private string litterise(long l)
        {
             string s="" ;
             while (l >= 27) ;
             {
                 s = s + (char)((byte)(l %27)+96);
               rtb.AppendText(s);
        l = (long)((l - (l % 27)) / 27);
             }
                return s;
        }

        private string litterise(long l)
        {
            string s = "";
            while (l >= 27) ;
            {
                s = s + (char)((byte)(l % 27) + 96);
             l = (long)((l - (l % 27)) / 27);
            }
            return s;
        }
        
        private void button1_Click(object sender, EventArgs e)
        {
         rtb.AppendText( litterise(long.Parse(tb1.Text)));    
        }