public static void SelectedService(int serviceId) { ProductManager productManager = new ProductManager(); if (serviceId == 1) { Console.Write("Enter product id: "); int productId = ConsoleInputValidator.ServiceInputValidator(serviceId); int quantity = ConsoleInputValidator.QuantityInputValidator(serviceId); if (_cartManager.Retrieve(productId) != null) { _cartManager.Update(_cartManager.Retrieve(productId), serviceId, quantity); } else { _cartManager.Add(productManager.Retrieve(productId), quantity); } DisplayHandler.DisplayService(); } else if (serviceId == 2) { Console.Write("Choose which ID to decrease/remove: "); int productId = ConsoleInputValidator.ServiceInputValidator(serviceId); int quantity = ConsoleInputValidator.QuantityInputValidator(serviceId); _cartManager.Update(_cartManager.Retrieve(productId), serviceId, quantity); DisplayHandler.DisplayService(); } else if (serviceId == 3) { Console.Write("Please enter cash on hand: "); ConsoleInputValidator.ServiceInputValidator(serviceId); DoTransactionAgain(); } }