具有意外输出的其他循环

Question

我有这段代码，但我不明白输出结果。我期待输出 121。我想了解这个特定函数而不是阶乘函数。

代码：

function a($num) {
    static $totFac = 1;

    if($num > 0){
        $totFac = $totFac * $num;
        a($num - 1);
    }

    $totFac++;
    return $totFac;
}

$result = a(5);
echo 'result: '.$result;

输出：

Answer 1

首先，5的阶乘为120解释为：
```
5! = 5 x 4 x 3 x 2 x 1 = 120
```

其次，递归调用时阶乘应该是这样的：

function factorial($number) {
    if ($number < 2) { 
        return 1; 
    } else { 
        return ($number * factorial($number-1)); 
    } 
}

如果你不是指阶乘，那么如果我改变你的函数就会发生这种情况

function a($num) {
    static $totFac = 1;

    if($num > 0){
        $totFac = $totFac * $num;
        echo "calc totFac: " . $totFac . "\n";
        a($num - 1);
    }

    $totFac++;
    echo "increment totFac: " . $totFac . "\n";
   return $totFac;
}

$result = a(5);
echo 'result: '.$result;

这是回显的输出

calc totFac: 5
calc totFac: 20
calc totFac: 60
calc totFac: 120
calc totFac: 120
increment totFac: 120
increment totFac: 121
increment totFac: 122
increment totFac: 123
increment totFac: 124
increment totFac: 125
result: 126

Answer 2

<?php
function a($num) {
    static $totFac = 1;
    if($num > 0){
        $totFac = $totFac * $num;
        echo 'totfac: '.$totFac . "<br>";
        return a($num - 1); //you have to return here to stop execution
    } else {
        $totFac++;
        return $totFac;
    }
}
$result = a(5);
echo 'result: '.$result;
?>

看评论解释

具有意外输出的其他循环

Other loop with unexpected output

php

algorithm

recursion

factorial