php variables - unexpected results

Question

I am just learning about php and i cant understand why i get different results from the two following code snippets.

Snippet 1:

<?php
    $x = 22;
    $y = 12;
    $counter = 0;

    function add()
    {
        if ($GLOBALS['counter'] == 0) 
        {
            $GLOBALS['z'] = $GLOBALS['x'] + $GLOBALS['y'];
        }
        else
        {
            $GLOBALS['z'] += $GLOBALS['y'];
        }
        $GLOBALS['counter'] ++;
    }

    add();
    echo "$z <br>";
    add();
    echo "$z <br>";
?>

the first returns 34 , 46 as expected.

Snippet 2:

<?php
    $x = 22;
    $y = 12;
    $counter = 0;

    function add()
    {
        if ($GLOBALS['counter'] == 0) 
        {
            $GLOBALS['z'] = $GLOBALS['x'] + $GLOBALS['y'];
        }
        else
        {
            $GLOBALS['z'] += $GLOBALS['y'];
        }
        $GLOBALS['counter'] ++;
    }

    for ($x=0; $x < 2; $x++) 
    { 
        add();
        echo "$z <br>";
    }
?>

The second returns 12 , 24.

This may sound very simple but i can honestly not work out why this isn't working.

Any help is appreciated.

If I understand your logic, shouldn't you be using for ($counter=0; $counter < 2; $counter++) since, you're setting x to be 0, you're going to get 12 and 24 returned — Karl
– Karl, Commented Feb 12, 2014 at 23:22
You are reseting $x to another value in your for loop. Try to AVOID using globals though: they're difficult to debug, hinder testing, and are generally frowned upon. — Wrikken
– Wrikken, Commented Feb 12, 2014 at 23:22

Paul · Accepted Answer · 2014-02-12 23:22:09Z

2

You are reusing the variable name $x for your loop counter. You're setting $x to 0, so you get 0 + 12 when you do $_GLOBALS['x'] + $_GLOBALS['y']. You must rename it to something you're not already using. I recommend changing it to $i:

for ($i = 0; $i < 2; $i++) 
{ 
    add();
    echo "$z <br>";
}

I also recommend that you avoid using $_GLOBALS in general.

answered Feb 12, 2014 at 23:22

Paul

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1 Comment

Matt_WOT Over a year ago

I cant believe I didn't notice that! thanks a lot for everyone's responses.

Floris · Accepted Answer · 2014-02-12 23:22:25Z

1

When you create a loop

for ($x=0; $x < 2; $x++) 
{ 
    add();
    echo "$z <br>";
}

You overwrite the definition of x from earlier... Change it to

for ($q=0; $q < 2; $q++) 
{ 
    add();
    echo "$z <br>";
}

and you'll see...

answered Feb 12, 2014 at 23:22

Floris

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