开关不适用于数字比较用例 [英] Switch doesn't work with numeric comparison cases

问题描述

这是我的代码.

$value = 0;
switch($value) {
      case ( $value <= 25 ):
            $CompScore = 'low';
            break;
      case ($value > 25 && $value <= 50 ):
            $CompScore = 'fair';
            break;
      case ($value > 50 && $value <= 75 ):
            $CompScore = 'good';
            break;
      case ($value >75 ):
            $CompScore = 'excellent';
            break;
      default:
            $CompScore = 'low';
            break;
}

echo $CompScore;

当值为0时，$compScore为fair.为什么不显示low?我不明白为什么.

When the value is 0, $compScore is fair. Why it is not showing low? I don't understand why.

推荐答案

您传递到switch语句中的值基本上就是switch语句寻找要评估的匹配项的内容，从案例列表的顶部到底部一直到它找到一个等于的(松散比较)，例如true == true.

The value you pass into a switch statement is basically what the switch statement looks for an evaluated match for, going from top to bottom down the list of cases until it finds one it is equal to (loose comparison), e.g. true == true.

在您的示例中，您的比较被评估为布尔值(对或错)-您的变量$value为设置为零，即与false相等(等于)，但对false而言，相同(严格比较).例如:

In your example, your comparisons are evaluated as booleans (true or false) - your variable $value is set to zero, which is equal to false, but not identical (strict comparison) to false. For example:

(0 == false)    // true
(0 === false)   // false
(1 == false)    // false
(1 === false)   // false
(1 == true)     // true
(1 === true)    // false
(true === true) // true

因此，通过使用布尔值true作为切换值，您可以执行以下操作:在语句内包含数字比较，其中每个比较的结果将为true或false，以匹配/不匹配原始的true值(布尔-布尔比较).

So by using a boolean true as your switch value, you can do this to have numeric comparison inside the statement, where each comparison will evaluate to either true or false to match/not match the original true value (boolean - boolean comparison).

switch(true) {
       case ($value <= 25):                 // true
             $CompScore = 'low';
             break;
       case ($value > 25 && $value <= 50 ): // false
             $CompScore = 'fair';
             break;
       case ($value > 50 && $value <= 75 ): // false
             $CompScore = 'good';
             break;
       case ($value >75 ):                  // false
             $CompScore = 'excellent';
             break;
       default:                             // if you removed the first case
             $CompScore = 'low';            // this default case would be used
             break;                         
 }

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