HP also stores all global variables in an array called $GLOBALS[index]. The index holds the name of the variable. This array is also accessible from within functions and can be used to update global variables directly.

<?php
  $x = 70;
  $y = 7;

  function myNum {
    $GLOBALS['y'] = $GLOBALS['x'] + $GLOBALS['y'];
  }
  
  myNum();
  echo $y; // output is 77
?>