private void btnBooking_Click(object sender, EventArgs e)
        {
            int         BookID = 0;
            int         qty    = 0;
            List <Book> books  = DBConnection.findBook(txtISBN.Text);

            foreach (var item in books)
            {
                BookID = item.BookID;
                qty    = item.Qty;
            }
            if (qty >= Convert.ToInt32(numQty.Value))
            {
                DBConnection.bookingBook(customer.CustomerID, BookID, Convert.ToInt32(numQty.Value), dateOfOreder.Value);
                DBConnection.updateBookQty(Convert.ToInt32(numQty.Value), BookID);
                MessageBox.Show("Book is booked");
            }
            else
            {
                MessageBox.Show("The Book's quantity is not enough");
            }
        }