2nd file:
<?php
$test = array();
function sup() {
    global $test;
    array_push($test, "0");
}
//So it wont say 0 because i didnt call sup() yet until the other page which is after the include once
echo $test[0];

1st File:

<?php
require_once('test.php');
sup();
//now it will say 0
echo $test[0];
?>