unexpected cast to boolean? - php

Question

Given this input: http://example.com/item.php?room=248&supply_id=18823, the following 2 blocks ought to produce the same result. Why don't they? What am I missing other than coffee?
This block gives the expected values:
if (isset($_GET['supply_id']) && isset($_GET['room'])) {
$id=validkey($_GET['supply_id']); //18823
$room=validkey($_GET['room']); //248
$arr=array('s'=>$id,'r'=>$room); //s=>18823, r=>248
}
But if I do the check and the assignment in one step, $id ends up equal to 1 instead of 18823. Why?
if (isset($_GET['supply_id']) && isset($_GET['room'])) {
if($id=validkey($_GET['supply_id']) && $room=validkey($_GET['room']))
$arr=array('s'=>$id",'r'=>$room); //s=>1, r=>248
}
This is the function I'm using:
function validkey($value){
if(is_scalar($value)){
$value=(int)$value;
return ($value>0) ? $value : false;
}
return false;
}

Answer 1

You should use parentheses:
if(($id=validkey($_GET['supply_id'])) && ($room=validkey($_GET['room'])))
Otherwise the result of validkey($_GET['supply_id']) && $room=validkey($_GET['room']) is assigned to $id variable because && operator has higher precedence than =

Answer 2

The && operator binds stronger than the = operator.
So your code basically becomes if ($id = (validkey($_GET['supply_id']) && $room = validkey($_GET['room'])))
--> Add parenthesis around the $foo = $bar expressions in your IF statement.

Answer 3

You seem to have a small error in your second example - a stray doubble quote after $id. Also, your second approach is generally frowned upon (assigning variables in an if construct) as it makes code considerably harder to follow. Clearer would be the following:
if (isset($_GET['supply_id']) && isset($_GET['room'])) {
$id=validkey($_GET['supply_id']); //18823
$room=validkey($_GET['room']); //248
if($id && $room) {
$arr=array('s'=>$id,'r'=>$room); //s=>18823, r=>248
}
}