public static void EditMenuItem(ref RestaurantManager restaurantManager) { Console.WriteLine("Enter the number you want to change:"); string editStr = Console.ReadLine(); while (string.IsNullOrWhiteSpace(editStr)) { Console.WriteLine("Error! Enter the number correctly!"); editStr = Console.ReadLine(); } Console.WriteLine("Enter the price you want to change:"); string priceStr = Console.ReadLine(); double price; while (!double.TryParse(priceStr, out price) || price < 0) { Console.WriteLine("Error! Enter the price correctly!"); priceStr = Console.ReadLine(); } Console.WriteLine("Enter the name you want to change:"); string itemName = Console.ReadLine(); while (string.IsNullOrWhiteSpace(itemName)) { Console.WriteLine("Error! Enter the item name correctly!"); itemName = Console.ReadLine(); } restaurantManager.EditMenuItem(itemName, price, editStr); }