private void btnModify_Click(object sender, EventArgs e)
        {
            frmModifyCustomer modifyCustomerForm = new frmModifyCustomer();

            modifyCustomerForm.addCustomer = false;
            modifyCustomerForm.customer    = customer;
            DialogResult result = modifyCustomerForm.ShowDialog();

            if (result == DialogResult.OK)
            {
                customer = modifyCustomerForm.customer;
                this.DisplayCustomer();
            }
            else if (result == DialogResult.Retry)
            {
                this.GetCustomer(customer.CustomerId);
                if (customer != null)
                {
                    this.DisplayCustomer();
                }
                else
                {
                    this.ClearControls();
                }
            }
        }
        private void btnAdd_Click(object sender, EventArgs e)
        {
            frmModifyCustomer addCustomerForm = new frmModifyCustomer();

            addCustomerForm.addCustomer = true;
            DialogResult result = addCustomerForm.ShowDialog();

            if (result == DialogResult.OK)
            {
                customer           = addCustomerForm.customer;
                txtCustomerId.Text = customer.CustomerId.ToString();
                this.DisplayCustomer();
            }
        }