php – change initial array inside the foreach loop?

I don’t think this is possible with a foreach loop, at least the way you wrote it : doesn’t seem to just be the way foreach works ; quoting the manual page of foreach :

Note: Unless the array is referenced, foreach operates on a copy
of the specified array and not the
array itself.

Edit : after thinking a bit about that note, it is actually possible, and here’s the solution :

The note says “Unless the array is referenced” ; which means this portion of code should work :

$i = 0;
$array = array('red', 'blue');
foreach($array as $key => & $value) {
    $array[] = 'white';
    echo $value . '<br />';
    if ($i++ >= 5) {
        break;   // security measure to ensure non-endless loop
    }
}

Note the & before $value.

And it actually displays :

red
blue
white
white
white
white

Which means adding that & is actually the solution you were looking for, to modify the array from inside the foreach loop 😉

Edit : and here is the solution I proposed before thinking about that note :

You could do that using a while loop, doing a bit more work “by hand” ; for instance :

$i = 0;

$array = array('red', 'blue');

$value = reset($array);
while ($value) {
    $array[] = 'white';
    echo $value . '<br />';
    if ($i++ >= 5) {
        break;   // security measure to ensure non-endless loop
    }
    $value = next($array);
}

Will get you this output :

red
blue
white
white
white
white

What you need to do is move the assignment inside the for loop and check the length of the array every iteration.

$array = array('red', 'blue');
for($i = 0; $i < count($array); $i++)
{
   $value = $array[$i];
   array_push($array, 'white');
   echo $value . '<br />';
}

Be careful, this will cause an infinite loop (white will be added to the end of the array at every loop).

Maybe you should use some other way, like:

$ar = array('blue', 'red');
while ($a = array_pop($ar) {
     array_push($ar, 'white');
}

Or something like this…

You can access the array by using the $key

$array = array('red', 'blue');
foreach($array as $key => $value) {
    $array[$key] = 'white';
}

In order to be able to directly modify array elements within the loop
precede $value with &. In that case the value will be assigned by
reference. [source]

All you have to do to your old code is

precede $value with &

like so

$array = array('red', 'blue');
foreach($array as $key => &$value) {// <-- here
    $array[] = 'white';
    echo $value . '<br />';
}

A while loop would be a better solution.

while (list ($key, $value) = each ($array) ) {
    $array[] = 'white';
    echo $value . '<br />';
}

If you don’t need the $key variable, as your example suggests then using $value = array_pop($array) instead if list ($key, $value) = each ($array) would be a less expensive option. see @enrico-carlesso’s Answer Here

As your array is sequantial(numeric,indexed) and not associative then you could use a for loop instead.

for ($key = 0; $key < count($array); ++$key) {
    $value = $array[$i];

    $array[] = 'white';
    echo $value . '<br />';
}

As a side note.

I don’t understand why its &$value and not &array.

&$value would suggest you can only modify the current element within the loop.
&array would suggest you could modify all array elements within the loop, including adding/removing element.