嵌套的php三元麻烦:三元输出！= if-else [英] nested php ternary trouble: ternary output != if - else

问题描述

我相当有能力使用PHP三元运算符.但是，在尝试弄清楚为什么下面的代码与if-else等效结构不匹配时，我遇到了障碍.该测试在不同的编号上运行了3次.每个结构的输出都在代码下方.

I am fairly capable at using the PHP ternary operator. However I have hit a roadblock at trying to figure out why the code below does not match the if-else equivalent structure. The test was run three times on different numbers. The output for each structure is below the code.

三元组:

$decimal_places = ($max <= 1) ? 2 : ($max > 3) ? 0 : 1;

三元输出:

最大值:-100000十进制:0

max: -100000 decimal: 0

最大值:0.48十进制:0

max: 0.48 decimal: 0

最大值:0.15十进制:0

max: 0.15 decimal: 0

If-Else

if($max <= 1)
 $decimal_places = 2;
elseif($max > 3)
 $decimal_places = 0;
else
 $decimal_places = 1;

If-Else输出:

If-Else Output:

最大值:-100000十进制:2

max: -100000 decimal: 2

最大值:0.48十进制:2

max: 0.48 decimal: 2

最大值:0.15十进制:2

max: 0.15 decimal: 2

谁能告诉我为什么这两个控制结构不能输出相同的数据?

Can anyone please tell me why the these two control stuctures do not output the same data?

推荐答案

您的右侧三元表达式需要用括号括起来，这样它就可以作为一个单独的表达式求值:

Your right-hand-side ternary expression needs to be wrapped in parentheses so it'll be evaluated by itself as a single expression:

$decimal_places = ($max <= 1) ? 2 : (($max > 3) ? 0 : 1);

// Another way of looking at it
$decimal_places = ($max <= 1)
                ? 2
                : (($max > 3) ? 0 : 1);

否则，您的三元表达式从左到右求值，结果是:

Otherwise your ternary expression is evaluated from left to right, resulting in:

$decimal_places = (($max <= 1) ? 2 : ($max > 3)) ? 0 : 1;

// Another way of looking at it
$decimal_places = (($max <= 1) ? 2 : ($max > 3))
                ? 0
                : 1;

翻译成if-else的文字变成这样:

Which, translated to if-else, becomes this:

if ($max <= 1)
    $cond = 2;
else
    $cond = ($max > 3);

if ($cond)
    $decimal_places = 0;
else
    $decimal_places = 1;

因此，对于$max以外的所有$max值，$decimal_places都以0结尾，在这种情况下，其值将为1.

Therefore $decimal_places ends up as 0 for all values of $max except 2, in which case it evaluates to 1.

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