Encryption and Decryption

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 CESAR1
{
    public partial class Opcionet1 : Form
    {
        public Opcionet1()
        {
            InitializeComponent();
        }
        Enkripto_Dekripto objEnkDek = new Enkripto_Dekripto();
        public void btnZhvendos_Click()
        {

            if (txtAlfabeti.Text.Length != 0)
            {
                txtAlfCesari.Clear();
                int Total = txtAlfabeti.Text.Length;
                char[] c;
                int p;
                int Celesi = Convert.ToInt16(txtCelesiOpcionet.Text);
                c = txtAlfabeti.Text.ToCharArray(0, Total);


                for (int i = 0; i < Total; i++)
                {
                    if (c[i] > 64 && c[i] < 91)
                    {
                        objEnkDek.k = objEnkDek.k + 1;
                        p = (char)c[i];
                        p = p - 65;
                        if ((Celesi >= 0) && (Celesi <= 26))
                        {
                            objEnkDek.CelesiMemorik = Celesi;
                            p = p + Celesi;
                            p = p % 26;
                            p = p + 65;
                            c[i] = (char)p;
                        }
                        else
                        {
                            MessageBox.Show("Celesi duhet te jete numer pozitiv mbrenda 0-26");
                            txtCelesiOpcionet.Text = "0";
                            Celesi = 0;
                        }
                    }
                    else if (c[i] > 96 && c[i] < 123)
                    {
                        objEnkDek.k = objEnkDek.k + 1;
                        p = (char)c[i];
                        p = p - 97;
                        if ((Celesi >= 0) && (Celesi <= 26))
                        {
                            p = p + Celesi;
                            p = p % 26;
                            p = p + 97;
                            c[i] = (char)p;
                        }
                        else
                        {
                            MessageBox.Show("Celesi duhet te jete numer pozitiv mbrenda 0-26");
                            txtCelesiOpcionet.Text = "0";
                            Celesi = 0;
                        }
                    }

                    txtAlfCesari.AppendText(c[i].ToString());
                }
            }
            else
            {
                MessageBox.Show("Ju lutem Mbushni Text per te Enkriptuar");
            }
        }

    }
}