private void search_vuncher()
        {
            SqlConnection con = new SqlConnection(dbclass.constring);
            try
            {
                string query = "SELECT Vuncher from tbl_customer";
                SqlCommand cmd = new SqlCommand(query, con);
                con.Open();
                SqlDataReader reader = cmd.ExecuteReader();
                AutoCompleteStringCollection Mycollection = new AutoCompleteStringCollection();
                while (reader.Read())
                {
                    Mycollection.Add(reader.GetString(0));
                }
                 txt_vuncher.AutoCompleteCustomSource = Mycollection;

                con.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            finally
            {
                con.Close();
            }
        }