use of $GLOBALS in php

Question

I am new to php so I do not know much about $_GLOBALS. I expect these are used to access global variables anywhere. So, my question is what is the problem inside function addition(), why I cannot do this? Can't I directly assign a value to the variable z.

    <?php 
    $x = 75; 
    $y = 25;

    function addition () { 
        $z = $GLOBALS['x'] + $GLOBALS['y']; 
    }

    addition(); 
    echo $z; 
    ?>

I get following error:

Notice: Undefined variable: z in C:\xampp\htdocs\php\first.php on line 14

which is echo $z;

Answer 1

If you start with programming I can highly recommend you not to use GLOBALS. There are better ways to get object/variable than globals. For example dependency injection

Function is something what takes arguments does something with them and return value. So you can create addition function

function addition ($x, $y) {
  return $x + $y;
}

when invoked this will return sum of $x and $y. When you have this value you can for example output it to user with echo

echo addition(5, 4);

or

 $z = addition(5, 4);
 echo $z;

In your case you get notice because you want to get variables that are not set. You can check if variable is set with function isset($variable)

If you still want to use $_GLOBALS then you need to know what $_GLOBALS is. It's reference for all variables in global scope so to make it work you should write something like

$x = 5;
$y = 7;

function addition() { 
    return  $GLOBALS['x'] + $GLOBALS['y']; 
}

echo addition();

But this is bad approach and I better don't do it.

Edit:

Check also this link