public static void startApp() { var services = new Services(); Console.WriteLine("Enter Username"); var username = new User(Console.ReadLine()); services.appInfo(); bool productsShop = true; while (productsShop) { var getUserInput = 0; bool isValidInput = Int32.TryParse(Console.ReadLine(), out getUserInput); if (isValidInput == false || getUserInput < 1 || getUserInput > 8) { Console.WriteLine("Your input is invalid. Please try aghain."); } switch (getUserInput) { case 1: services.printVendors(); break; case 2: services.printProductsByVendors(); break; case 3: services.searchByProductName(); break; case 4: services.ascDescProductItems(); break; case 5: services.ascDescProductItemsByPrice(); break; case 6: services.orders(); break; } } }