Increase Performance of Loop with Large Arrays

In PHP, this is how we usually loop through arrays:

<?php
for ($i=0; $i<count($big_array); $i++){
 //
}
?>

Having this approach, program will try to count the $big_array every time it loops and it may cause some performance issues. To make it more efficient, we should code it this way:

<?php
for ($i=0, $n=count($big_array); $i<$n; $i++){
 //
}
?>

It does the counting during initialization only.