private void Products_SelectedIndexChanged(object sender, EventArgs e)
 {
     Quantity.Text = bc.getQuantity(Int32.Parse(Products.SelectedValue.ToString())).ToString();
     total         = Int32.Parse(Quantity.Text);
     c             = total;
     if (c == 0)
     {
         AddToOutvoice.Enabled = false;
     }
     else
     {
         AddToOutvoice.Enabled = true;
     }
 }