 <?php
 
$a = 10;
$b = 20;
 
function add() {
  $GLOBALS['sum'] = $GLOBALS['a'] + $GLOBALS['b'];
}
 
add();
echo $sum;

	<?php

	$a = 10;
	$b = 20;

	function add() {
	$GLOBALS['sum'] = $GLOBALS['a'] + $GLOBALS['b'];
	}

	add();
	echo $sum;