private void btnAdd_Click(object sender, EventArgs e)
        {
            frmAddModifyCustomer addCustomerForm = new frmAddModifyCustomer();

            addCustomerForm.AddCustomer = true;

            DialogResult result = addCustomerForm.ShowDialog();

            if (result == DialogResult.OK)
            {
                var customer = addCustomerForm.Customer;
                customerIDTextBox.Text = customer.CustomerID.ToString();
                DisplayCustomer(customer);
            }
        }
        private void btnModify_Click(object sender, EventArgs e)
        {
            if (Customer == null)
            {
                MessageBox.Show(Properties.Resources.ModifyCustomerNoCustomerFoundMessage, Properties.Resources.ModifyCustomerNoCustomerFoundCaption, MessageBoxButtons.OK, MessageBoxIcon.Error);
                return;
            }

            frmAddModifyCustomer modifyCustomerForm = new frmAddModifyCustomer();

            modifyCustomerForm.AddCustomer = false;
            modifyCustomerForm.Customer    = Customer;

            DialogResult result = modifyCustomerForm.ShowDialog();

            if (result == DialogResult.OK)
            {
                var customer = modifyCustomerForm.Customer;
                DisplayCustomer(customer);
            }
        }