C＃开关问题 [英] c# switch problem

问题描述

我是新来编程，并具有下列代码的问题：

I'm new to programming and having a problem with the following code:

    private string alphaCoords(Int32 x)
    {
        char alphaChar;

        switch (x)
        {
            case 0: alphaChar = 'A'; break;
            case 1: alphaChar = 'B'; break;
            case 2: alphaChar = 'C'; break;
            case 3: alphaChar = 'D'; break;
            case 4: alphaChar = 'E'; break;
            case 5: alphaChar = 'F'; break;
            case 6: alphaChar = 'G'; break;
            case 7: alphaChar = 'H'; break;
            case 8: alphaChar = 'I'; break;
            case 9: alphaChar = 'J'; break;
        }

        return alphaChar.ToString();
    }

编译器说：未分配的局部变量的使用alphaChar

The compiler says: Use of unassigned local variable 'alphaChar'

但我在我的开关模块分配它。

But I'm assigning it in my switch block.

我敢肯定，这是我的错，因为我不知道够了有关编程。

I'm sure this is my fault as I dont know enough about programming.

请指教。

感谢。

推荐答案

你分配给它的如果的x是0-9。你会期望它做的，如果 X 被123有关系吗？虽然的您的可能知道，0到9之间只值将被传递中，编译器不 - 这样的是的需要考虑什么，否则会发生

You're assigning it if x is 0-9. What would you expect it to do if x were 123 though? While you may know that only values between 0 and 9 will be passed in, the compiler doesn't - so it needs to consider what would happen otherwise.

要避免这种情况的一种方法是在你的switch语句，你可以用它来抛出，如果一个异常默认情况值不在预期范围：

One way to avoid this is to have a default case in your switch statement, which you can use to throw an exception if the value isn't in the expected range:

switch (x)
{
    case 0: alphaChar = 'A'; break;
    case 1: alphaChar = 'B'; break;
    case 2: alphaChar = 'C'; break;
    case 3: alphaChar = 'D'; break;
    case 4: alphaChar = 'E'; break;
    case 5: alphaChar = 'F'; break;
    case 6: alphaChar = 'G'; break;
    case 7: alphaChar = 'H'; break;
    case 8: alphaChar = 'I'; break;
    case 9: alphaChar = 'J'; break;
    default: throw new ArgumentOutOfRangeException();
}

下面是虽然稍微简单替代，后者完全消除您的switch语句：

Here's a slightly simpler alternative though, which removes your switch statement completely:

if (x < 0 || x > 9)
{
    throw new ArgumentOutOfRangeException();
}
char alphaChar = (char)('A' + x);

请注意，您的做的需要使用算术这样的时候必须小心。在Java和C＃的基本表示保证是Unicode的，这让生活变得更加简单。我相信这是罚款这样的事情（和六角解析/格式化），但是当你冒险进入更奇特的场景，它会失败。话又说回来，这对很多代码简化技术真的......如果是不恰当地使用它们，你结束了一个烂摊子。

Note that you do need to exercise care when using arithmetic like this. In Java and C# the underlying representation is guaranteed to be Unicode, which makes life a lot easier. I believe it's fine for things like this (and hex parsing/formatting) but when you venture into more exotic scenarios it would fail. Then again, that's true for a lot of code simplification techniques... if they're applied inappropriately, you end up with a mess.

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