切换语句在c#中失败?

Switch语句贯穿是我个人喜欢Switch vs. if/else if结构的主要原因之一。下面是一个例子:

static string NumberToWords(int number)
{
    string[] numbers = new string[] 
        { "", "one", "two", "three", "four", "five", 
          "six", "seven", "eight", "nine" };
    string[] tens = new string[] 
        { "", "", "twenty", "thirty", "forty", "fifty", 
          "sixty", "seventy", "eighty", "ninety" };
    string[] teens = new string[]
        { "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen",
          "sixteen", "seventeen", "eighteen", "nineteen" };

    string ans = "";
    switch (number.ToString().Length)
    {
        case 3:
            ans += string.Format("{0} hundred and ", numbers[number / 100]);
        case 2:
            int t = (number / 10) % 10;
            if (t == 1)
            {
                ans += teens[number % 10];
                break;
            }
            else if (t > 1)
                ans += string.Format("{0}-", tens[t]);
        case 1:
            int o = number % 10;
            ans += numbers[o];

            break;
        default:
            throw new ArgumentException("number");
    }
    return ans;
}

聪明的人畏缩不前，因为字符串[]应该在函数之外声明:好吧，它们是，这只是一个例子。

编译器失败，出现以下错误:

Control cannot fall through from one case label ('case 3:') to another
Control cannot fall through from one case label ('case 2:') to another

为什么?有没有什么方法能让这种行为不需要三个如果呢?

当前回答

“为什么”是为了避免意外摔倒，对此我很感激。这是C和Java中常见的错误来源。

解决办法是使用goto，例如。

switch (number.ToString().Length)
{
    case 3:
        ans += string.Format("{0} hundred and ", numbers[number / 100]);
        goto case 2;
    case 2:
    // Etc
}

在我看来，开关/机箱的总体设计有点不太理想。它太接近C语言了——在范围等方面可以做一些有用的改变。可以说，一个更聪明的开关，可以进行模式匹配等将是有帮助的，但这实际上是从开关到“检查条件序列”的变化-在这一点上，可能需要一个不同的名称。

2008-10-06 13:13:42

其他回答

你可以“转到案例标签” http://www.blackwasp.co.uk/CSharpGoto.aspx

The goto statement is a simple command that unconditionally transfers the control of the program to another statement. The command is often criticised with some developers advocating its removal from all high-level programming languages because it can lead to spaghetti code. This occurs when there are so many goto statements or similar jump statements that the code becomes difficult to read and maintain. However, there are programmers who point out that the goto statement, when used carefully, provides an elegant solution to some problems...

2008-10-06 13:08:37

开关失效在历史上是现代软件的主要漏洞来源之一。语言设计人员决定强制在case的末尾跳转，除非您默认直接跳转到下一个case而不进行处理。

switch(value)
{
    case 1:// this is still legal
    case 2:
}

2008-10-06 13:06:10

(复制/粘贴我在其他地方提供的答案)

通过在case中没有代码(见case 0)，或使用特殊的goto case(见case 1)或goto default(见case 2)表单，可以实现切换情况:

switch (/*...*/) {
    case 0: // shares the exact same code as case 1
    case 1:
        // do something
        goto case 2;
    case 2:
        // do something else
        goto default;
    default:
        // do something entirely different
        break;
}

2008-10-06 13:13:18

他们故意省略了这种行为，以避免这种行为不是由意志决定的，而是引起问题的。

它只能在case部分没有语句的情况下使用，例如:

switch (whatever)
{
    case 1:
    case 2:
    case 3: boo; break;
}

2008-10-06 13:04:34

跳转语句(例如break)是每个案例块后要求，包括最后一个块是否 case语句或默认值声明。只有一个例外，不像 c++的switch语句)，c#没有支撑着一种含蓄的坠落一个箱子连着另一个箱子。一个例外是如果case语句有没有代码。

——c# switch()文档

2008-10-06 13:03:34

切换语句在c#中失败?

推荐文章

最新文章

标签