PHP endless loop, why?

Question

Here is my code. I don't understand why am I in endless loop. I think $check has to stop the loop when I make unique random values for my array.

    <?php

        $foo["blue"] = 0;
        $foo["black"] = 0;
        $foo["red"] = 0;
        $foo["white"] = 0;

        $check;
        do
        {
            foreach($foo as &$val)
            {
                $val = rand(1,6);
            }

            $foo = array_unique($foo);
            $check = count($foo);

        }
        while($check != 4);

        echo '............................ <br>';
        foreach($foo as $key=>$value)
        {
            echo $key . ' ' . $value . '<br>';
        }

    ?>

Try putting print_r($foo); in the do-while loop to see what the values are. — Barmar
– Barmar, Commented Sep 28, 2017 at 22:04
@ishegg That's OK, it's how you update the current array element in a foreach loop. — Barmar
– Barmar, Commented Sep 28, 2017 at 22:07
$foo = array_unique($foo). If, after the first iteration, the array has duplicated values, then that line will make $foo an array of three or less elements, and thus $check will always be different than 4, thus the loop will be infinite. The only way the loop will stop is if you get four different random values after the first iteration. — José A. Zapata
– José A. Zapata, Commented Sep 28, 2017 at 22:08

Barmar · Accepted Answer · 2017-09-28 22:12:14Z

The problem is that the first time through the loop there are some duplicates, so array_unique() reduces the array from 4 elements to 1, 2, or 3. The foreach loop can never make the array bigger again, because it's only looping over the elements that currently exist in the array. So once the array shrinks, it will never grow back to 4 elements, and $check != 4 will always be true.

You should get the original keys of the array and use that.

<?php

    $foo["blue"] = 0;
    $foo["black"] = 0;
    $foo["red"] = 0;
    $foo["white"] = 0;
    $keys = array_keys($foo);

    $check;
    do
    {
        foreach($keys as $i)
        {
            $foo[$i] = rand(1,6);
        }

        $foo = array_unique($foo);
        $check = count($foo);

    }
    while($check != 4);

    echo '............................ <br>';
    foreach($foo as $key=>$value)
    {
        echo $key . ' ' . $value . '<br>';
    }

?>

DEMO

Lawrence Cherone · Accepted Answer · 2017-09-28 22:07:53Z

0

Personally, I wouldn't do it in a loop with such low entropy as it could take all day to finally match a random set.

A better way would be to generate a range and randomise that, then loop over your array and set the value.

<?php
$rand = range(1, 6);
shuffle($rand);

$foo["blue"] = 0;
$foo["black"] = 0;
$foo["red"] = 0;
$foo["white"] = 0;

$i=0;
foreach ($foo as $key => $value) {
    $foo[$key] = $rand[$i];
    $i++;
}

print_r($foo);
/*Array
(
    [blue] => 1
    [black] => 3
    [red] => 2
    [white] => 5
)
*/

https://3v4l.org/4hPku

answered Sep 28, 2017 at 22:07

Lawrence Cherone

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