C＃Switch语句使用方法

Question

我必须编写一个程序，使用Method提示用户选择菜单。

我试着写点什么，但我失败了。 ：，（

这是我的代码。

class Program
{
    static void Main(string[] args)
    {


        Console.WriteLine("Choose a Menu");
        Console.WriteLine("1: Calculate Area");
        Console.WriteLine("2: Calculate Volume");
        Console.WriteLine("3: Calculate Surface Area");
        Console.WriteLine("0: Exit the program");

        int number = Convert.ToInt32(Console.ReadLine());

        Console.WriteLine(calculateTotal(number));


    }

    public static int calculateTotal(int number)
    {


        switch (number)
        {
            case 1:
                Console.WriteLine("Calculate Area");
                Console.Write("Input Length\t");
                int L1 = Convert.ToInt32(Console.ReadLine());
                Console.Write("Input Width\t");
                int W1 = Convert.ToInt32(Console.ReadLine());
                Console.Write("Area is\t");
                Console.WriteLine(L1 * W1);
                Console.ReadLine();
                break;
            case 2:
                Console.WriteLine("2: Calculate Volume");
                Console.Write("Input Length\t");
                int L2 = Convert.ToInt32(Console.ReadLine());
                Console.Write("Input Width\t");
                int W2 = Convert.ToInt32(Console.ReadLine());
                Console.Write("Input Height\t");
                int H2 = Convert.ToInt32(Console.ReadLine());
                Console.Write("Volume is\t");
                Console.WriteLine(L2 * W2 * H2);
                Console.ReadLine();
                break;
            case 3:
                Console.WriteLine("3: Calculate Surface Area");
                Console.Write("Input Length\t");
                int L3 = Convert.ToInt32(Console.ReadLine());
                Console.Write("Input Width\t");
                int W3 = Convert.ToInt32(Console.ReadLine());
                Console.Write("Surface Area is\t");
                Console.WriteLine(L3 * W3 * 2);
                Console.ReadLine();
                break;
            case 0:
                Console.WriteLine("Exit the program now");
                break;
            default:
                Console.WriteLine("ERROR: Invalid Choice");
                break;


        }
    }
}

这是我的问题

'Program.calculateTotal(int)':not all code paths return a value

我是编程的超级初学者 你能帮我找个问题吗？