private void btnBookARoom_Click(object sender, EventArgs e)
 {
     using (var subform = new BookARoomForm(mainForm))
     {
         subform.ShowDialog();
     }
 }
        private void btnChangeReservation_Click(object sender, EventArgs e)
        {
            var customerID = mainForm.GetSelectedCustomerID();
            var dbm        = new DBmanager();

            dbm.DeleteReservation(customerID);
            using (var subform = new BookARoomForm(mainForm))
            {
                subform.ShowDialog();
            }
            this.Close();
        }
        private void btnBookARoom_Click(object sender, EventArgs e)
        {
            if (listBoxSearchedCustomers.SelectedIndex > -1)
            {
                using (var subform = new BookARoomForm(this))
                {
                    subform.ShowDialog();
                }
            }
            else
            {
                MessageBox.Show("You need to choose customer first");
            }

        }