Passing by reference, you can change value inside or outside loop.
<?php
$a = array ('zero','one','two');
foreach ($a as &$v) {
}
// before loop $v is reference to last item in array $a
// if you perform unset($v) before this loop, nothing will change in $a
foreach ($a as $v) {
// here you assigning $v values from this array in loop
}
print_r($a);
// Array
// (
// [0] => zero
// [1] => one
// [2] => one
// )