How can I write in PHP a function that modifies an array?

Question

I would like to have a function that takes an array as input and changes some values of the array (in my case the array is $_SESSION but I think it does not really maters).

Answer 1

function change_array() {

     global $x; /*this will tell the function to work on the array 'x' out of the function itself.*/
     $x[0] = 100;

}