how to define a global variable inside a php function code example

Example 1: how make a variable global php

$a = 1;
$b = 2;
function Sum(){
    global $a, $b; // allows access to vars outside of function
    $b = $a + $b;
} 

Sum();
echo $b; // output is 3

Example 2: php globals

$GLOBALS["foo"]