gistfile1.txt

$ cat xx.php 
<?php
$a = array(1=>2);
foreach ($a as $key => $val) {
	$a[$key+1] = $val + 1;
}
var_dump($a);

$ sapi/cli/php xx.php 
array(2) {
  [1]=>
  int(2)
  [2]=>
  int(3)
}