Description:
------------
Reference value modification of element of array

Test script:
---------------
$a = ['23','25','26'];
foreach ($a as &$v) {
    $v = $v+1;
}
function get_check_code($data)
{
    foreach ($data as &$a) {
        $a = hexdec($a);
    }
    $sum = dechex(array_sum($data));
    return substr($sum, -2);
}
var_dump($a);
$b = get_check_code($a);
$c = array_merge($a,[$b]);
print_r($c);

Expected result:
----------------
var_dump($a) output array(3) { [0] => int(24) [1] => int(26) [2] => int(27) }

print_r($c) output Array ( [0] => 24 [1] => 26 [2] => 39 [3] => 71 )

Actual result:
--------------
The expected result of print_r($c) is Array ( [0] => 24 [1] => 26 [2] => 27 [3] => 71 )  or  Array ( [0] => 36 [1] => 38 [2] => 39 [3] => 71 )