C# 返回错误 “not all code paths return a value” - 如何查找不返回值的路径

Question

总的来说，我对编程还很陌生，所以我可能遗漏了一些非常明显的东西。但是，哪条路径会导致不返回值？

public static int CheckAge()
        {
            int userAge; 
            bool inValidInput = true;
            while (inValidInput)
            {
                Console.Write("Enter your age: ");
                string stringAge = Console.ReadLine();

                if (int.TryParse(stringAge, out userAge))
                {
                    switch (userAge)
                    {
                        case int n when (n < 1 || n > 120):
                            Console.ForegroundColor = ConsoleColor.Red;
                            Console.Write("RANGE ");
                            Console.ForegroundColor = ConsoleColor.White;
                            Console.Write("error\n");
                            Console.Write("Accepted range are numbers (eg. 123) ");
                            Console.ForegroundColor = ConsoleColor.Red;
                            Console.Write("between 1 and 120\n");
                            Console.ForegroundColor = ConsoleColor.White;
                            break;

                        default:
                        return userAge;
                    }
                }
                else
                {
                    Console.ForegroundColor = ConsoleColor.Magenta;
                    Console.Write("TYPE ");
                    Console.ForegroundColor = ConsoleColor.White;
                    Console.Write("error\n");
                    Console.Write("Accepted input types are ");
                    Console.ForegroundColor = ConsoleColor.Magenta;
                    Console.Write("numbers (eg. 123) ");
                    Console.ForegroundColor = ConsoleColor.White;
                    Console.Write("between 1 and 120\n");
                    continue;  
                }
            }
        }

当我看着它时，我觉得所有的路径最终都应该通向:

default:
   return userAge;

如果我需要提供完整的源代码，请告诉我，我会添加它，不想让它变得困惑，以防我只需要示例。

编辑:我真的很喜欢@oerkelens 给出的解决方案，但我正在努力让 userAge 变量正常运行。 下方 使用:(return userAge; inside if statement):

public static int CheckAge()
        {
            int userAge;
            bool inputIsValid = false;
            while (!inputIsValid)
            {
                Console.Write("Enter your age: ");
                string stringAge = Console.ReadLine();

                if (!int.TryParse(stringAge, out userAge))
                {
                    WriteNumericalError();
                    continue;
                }

                if (userAge < 1 || userAge > 120)
                {
                    WriteRangeError();
                    continue;
                }

                inputIsValid = true;
                return userAge;
            }
        }

给我老话:'Program.CheckAge()':并非所有代码路径都返回一个值

下面 使用:(return userAge; outside if statement):

public static int CheckAge()
        {
            int userAge;
            bool inputIsValid = false;
            while (!inputIsValid)
            {
                Console.Write("Enter your age: ");
                string stringAge = Console.ReadLine();

                if (!int.TryParse(stringAge, out userAge))
                {
                    WriteNumericalError();
                    continue;
                }

                if (userAge < 1 || userAge > 120)
                {
                    WriteRangeError();
                    continue;
                }

                inputIsValid = true;
            }
            return userAge;
        }

解决了“Program.CheckAge()”问题:并非所有代码路径都返回一个值，但引入了:使用未分配的局部变量“userAge”

最终解决方案

public static int CheckAge()
        {
            int userAge = 0;
            bool validInput = false;
            while (!validInput)
            {
                Console.Write("Enter your age: ");
                string stringAge = Console.ReadLine();

                if (!int.TryParse(stringAge, out userAge))
                {
                    WriteNumericalError();
                    continue;
                }

                if (userAge < 1 || userAge > 120)
                {
                    WriteRangeError();
                    continue;
                }
                validInput = true;
            }
            return userAge;
        }


        private static void WriteNumericalError()
        {
            Console.ForegroundColor = ConsoleColor.Magenta;
            Console.Write("TYPE ");
            Console.ForegroundColor = ConsoleColor.White;
            Console.Write("error\n");
            Console.Write("Accepted input types are numbers ");
            Console.ForegroundColor = ConsoleColor.Magenta;
            Console.Write("(eg. 1 2 3 4 5 6 7 8 9 0)\n");
            Console.ForegroundColor = ConsoleColor.White;
            Console.WriteLine("Press [Enter] to try again");
            Console.ReadLine();
        }

        private static void WriteRangeError()
        {
            Console.ForegroundColor = ConsoleColor.Red;
            Console.Write("RANGE ");
            Console.ForegroundColor = ConsoleColor.White;
            Console.Write("error\n");
            Console.Write("Your entered number does not fall within the accepted range ");
            Console.ForegroundColor = ConsoleColor.Red;
            Console.Write("1 to 5 for film choice - 1 to 120 for age input\n");
            Console.ForegroundColor = ConsoleColor.White;
            Console.WriteLine("Press [Enter] to try again");
            Console.ReadLine();
        }

Answer 1

首先，您正在使用一个模糊的无限循环。即使是 while (true)，这似乎也是一种代码味道。
其次，你的旗帜具有负面意义。这让人发疯。 inValidInput == false表示输入有效!
第三，很难看出您想用代码完成什么。

下面是一个解决这些问题的例子。还有其他可能的改进，但这只是一个开始。

public static int CheckAge()
{
    int userAge = 0; 
    bool inputIsValid = false;
    while (!inputIsValid)
    {
       Console.Write("Enter your age: ");
       string stringAge = Console.ReadLine();

       if (!int.TryParse(stringAge, out userAge))
       {
           WriteNumericalError();
           Continue;
       }
       
       if (userAge < 1 || userAge > 120) 
       {
           WriteRangeError();
           Continue;
       }

       inputIsValid = true;
   }
   return userAge;
}

private void WriteNumericalError()
{
    Console.ForegroundColor = ConsoleColor.Red;
    Console.Write("RANGE ");
    Console.ForegroundColor = ConsoleColor.White;
    Console.Write("error\n");
    Console.Write("Accepted range are numbers (eg. 123) ");
    Console.ForegroundColor = ConsoleColor.Red;
    Console.Write("between 1 and 120\n");
    Console.ForegroundColor = ConsoleColor.White;
}
private void WriteRangeError()
{
    Console.ForegroundColor = ConsoleColor.Magenta;
    Console.Write("TYPE ");
    Console.ForegroundColor = ConsoleColor.White;
    Console.Write("error\n");
    Console.Write("Accepted input types are ");
    Console.ForegroundColor = ConsoleColor.Magenta;
    Console.Write("numbers (eg. 123) ");
    Console.ForegroundColor = ConsoleColor.White;
    Console.Write("between 1 and 120\n");
}