Case 语句输出不正确? [英] Case statement is not outputting correctly?

问题描述

这很奇怪，但以下是我的案例陈述:

This is very strange but below is my case statement:

switch($grade){
    case ($average >70):
    $grade = 'A';
    break;
    case ($average >=60 && $average <=69):
    $grade = 'B';
    break;
    case ($average >=50 && $average <=59):
    $grade = 'C';
    break;

};

所以如果它的 70+ 是 A 级，60-69 B 级，50-59 C 级.

So if its 70+ it is grade A, 60-69 grade B, 50-59 grade C.

但它输出的是:60+ A级，50-59 B级，40-49 C级.

But instead it outputting this: 60+ grade A, 50-59 grade B, 40-49 grade C.

为什么要这样做，因为函数看起来是正确的?

Why is it doing this because function seems correct?

    echo "<p><strong>Average Mark:</strong> $average</p>";
    echo "<p><strong>Average Grade:</strong> $grade</p>";

推荐答案

正如其他人在评论中提到的，案例中的条件"应该是一个静态值，而不是一个逻辑表达式.

As others mentioned in comments, the "condition" in a case should be a static value, not a logical expression.

此外，您打开的值(在您的情况下，$grade)应该是您正在测试的值.您似乎在使用它作为关于您正在分配的变量的提示.

Also, the value you're switching on (in your case, $grade) should is the one you're testing. You appear to be using it as a hint about what variable you're assigning.

修复代码的最简单方法是使用 if-elseif-else 结构:

The simplest way to fix your code would be to use an if-elseif-else construct:

if ($average >70)
    $grade = 'A';
elseif ($average >=60 && $average <=69)
    $grade = 'B';
elseif ($average >=50 && $average <=59)
    $grade = 'C';

然而，为了说明 switch 语句的工作原理，您还可以执行以下操作:

However, to be perverse, and to illustrate how a switch statement works, you could also do the following:

switch(true){
    case ($average >70):
        $grade = 'A';
        break;
    case ($average >=60 && $average <=69):
        $grade = 'B';
        break;
    case ($average >=50 && $average <=59):
        $grade = 'C';
        break;
};

在这个例子中，我将值 true 依次与每个 case 进行比较，其中每个 case-values 实际上是评估布尔表达式的结果.值与 true 匹配的第一个表达式将触发.

In this example I'm comparing the value true to each of the cases in turn, where each of those case-values is actually the result of evaluating a boolean expression. The first expression whose value matches true will fire.

如果您不了解 switch 语句，可能没有太大帮助.

Probably not much help, if you don't understand switch statements.

编辑:我刚刚注意到逻辑上有一个差距:如果某人的平均分正好是 70 呢?使用像 switch 或 if-else 这样的级联语句，您可以消除一些冗余(在这种情况下是破坏性的)代码，因此:

Edit: I just noticed that there's a gap in the logic: what if someone's average is exactly 70? Using a cascading statement like a switch or if-else, you can eliminate some of the redundant (and in this case damaging) code, thus:

if ($average >=70)
    $grade = 'A';
elseif ($average >=60)
    $grade = 'B';
elseif ($average >=50)
    $grade = 'C';
// ...
else
    $grade = 'F';

...依此类推，直到您使用的最低等级.

...and so on, to whatever lowest grade you're using.

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