private void InputOrderQuantity(object sender, EventArgs e)
        {
            string textBoxValue = "";

            if (CustomLibrary.CheckTextisNumber(quantityTextBox.Text))
            {
                textBoxValue = quantityTextBox.Text;
            }
            else
            {
                quantityTextBox.Text = textBoxValue;
            }

            order.itemQuantity = (textBoxValue == "") ? 0 : int.Parse(textBoxValue);
            CalculateTotalPrice();
        }
        private void AddCustomerData(object sender, EventArgs e)
        {
            outputRichTextBox.Text = "";
            string message = "";

            try
            {
                if (order.name == "")
                {
                    message = "Please input name.";
                }
                if (order.contact == "")
                {
                    message = "Please input contact.";
                }
                if (order.menuItem == "")
                {
                    message = "Please select an item.";
                }
                if (order.itemQuantity == 0)
                {
                    message = "Please input order quantity.";
                }
                if (CustomLibrary.HasDuplicateContacts(customersOrders, order.contact))
                {
                    message = "Contact already exists. Please provide a different contact.";
                }


                if (message != "")
                {
                    MessageBox.Show(message);
                    return;
                }
                else
                {
                    OrderDetails newOrder = new OrderDetails(order.name, order.contact, order.menuItem, order.itemPrice, order.itemQuantity, order.totalPrice);
                    customersOrders.Add(newOrder);
                    outputRichTextBox.Text = newOrder.ShowOrderDetails();
                    Reset();
                }
            }
            catch (Exception exception)
            {
                MessageBox.Show(exception.Message);
            }
        }