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

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

其他回答

您忘记在情形3中添加“break;”语句。在情形2中，你把它写到if块中。因此，试试这个吧:

case 3:            
{
    ans += string.Format("{0} hundred and ", numbers[number / 100]);
    break;
}


case 2:            
{
    int t = (number / 10) % 10;            
    if (t == 1)            
    {                
        ans += teens[number % 10];                
    }            
    else if (t > 1)                
    {
        ans += string.Format("{0}-", tens[t]);        
    }
    break;
}

case 1:            
{
    int o = number % 10;            
    ans += numbers[o];            
    break;        
}

default:            
{
    throw new ArgumentException("number");
}

2008-10-06 13:10:37

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

switch (c#参考)说

c#要求开关部分的结尾，包括最后一个，

所以你还需要添加一个休息;到默认的部分，否则仍然会有编译器错误。

2014-10-07 09:33:53

你可以像c++一样通过goto关键字实现fall through。

EX:

switch(num)
{
   case 1:
      goto case 3;
   case 2:
      goto case 3;
   case 3:
      //do something
      break;
   case 4:
      //do something else
      break;
   case default:
      break;
}

2010-07-28 20:30:50

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

切换语句在c#中失败?

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