Why PHP variables are persistent within loop cycles?

Question

The following code should never execute like that in any other language that I know (C, C++, C#, etc.)

<?php

$do = true;

for($i=0; $i<3; $i++) {
    if($do===true) {
        $some_variable = 666;
        echo $some_variable;
        $do = false;
    }
    if(isset($some_variable)) {
        echo $some_variable;
    }
}

Why PHP won't unset a $some_variable in next loop iteration?

Possible duplicate of [Are PHP variables declared inside a foreach loop destroyed and re-created at each iteration?](http://stackoverflow.com/questions/13626812/are-php-variables-declared-inside-a-foreach-loop-destroyed-and-re-created-at-eac) — Patrick Q, Nov 03 '16 at 18:12
Seems like you can echo the variable outside the for loop even if you defined it inside. I think PHP treats those variables as some kind of global for the current page. The same won't apply for functions and classes tough — Phiter, Nov 03 '16 at 18:15
Possible duplicate of [PHP for ; foreach variable scope](http://stackoverflow.com/questions/34637603/php-for-foreach-variable-scope) — Charlotte Dunois, Nov 03 '16 at 18:16

score 0 · Accepted Answer · answered Nov 03 '16 at 18:09

Because it is set in the global scope. Once the first iteration sets it, the variable remains set.

http://php.net/manual/en/language.variables.scope.php

Here you can move the work to a function with its own scope. After the first iteration $do is set to false, and it no longer sets the variable:

$do = true;

function do_thing() {
    global $do;
    if($do===true) {
        $some_variable = 666;
        echo $some_variable;
        $do = false;
    }
    if(isset($some_variable)) {
        echo $some_variable;
    }
}

for($i=0; $i<3; $i++) {
    do_thing();
}

score 0 · Answer 2 · answered Nov 03 '16 at 18:14

Or, you can just make sure you unset the $some_variable in the first iteration.

<?php

$do = true;

for($i=0; $i<3; $i++) {

    if($do===true) {
        $some_variable = 666;
        // echo $some_variable;
        $do = false;
    }
    if(isset($some_variable)) {
        echo $some_variable;
        unset($some_variable);
    }

}

?>

The point is that since you create the $some_variable in the first run of the loop, it will be available in all the subsequent runs of the loop, unless you specifically unset it again.

Why PHP variables are persistent within loop cycles?

2 Answers2