switch case isset triggered when case is -not- set - php

Question

--Let me add this. This code works for me the way it is. I just do not know why it works.--
I can't figure this out.
switch ($_SERVER['QUERY_STRING']) {
case isset($_GET['test0']):
echo "test0<br>";
break;
case isset($_GET['test1']):
echo "test1<br>";
break;
case isset($_GET['test2']):
echo "test2<br>";
break;
case isset($_GET['test3']):
echo "test3<br>";
break;
case isset($_GET['test4']):
echo "test4<br>";
break;
default:
echo "no test<br>";
break;
}
When the url is index.php?test0, "test0" is shown.
When the url is index.php?test4, "test4" is shown.
When the url is index.php?test999, "no test" is shown.
When the url is index.php?tes, "no test" is shown.
When the url is index.php?, or index.php, "test0" is shown.
Why is this? The condition is not met, so should the default not be shown?

Answer 1

switch can't be used this way. isset() returns true or false, not something (a string, an int, etc) you can match against. What you are basically doing is:
switch ($_SERVER['QUERY_STRING']) {
case true:
echo "test0<br>";
break;
case true:
echo "test1<br>";
break;
case false:
echo "test2<br>";
break;
case false:
echo "test3<br>";
break;
case true:
echo "test4<br>";
break;
default:
echo "no test<br>";
break;
}
cases are considered from top to bottom. In this case, $_SERVER["QUERY_STRING"] is automatically type-converted to bool (which will return true in this case). The first case it sees would be test0, so it echos that. If you do that for test0-4, it will give you the false illusion that this code is working as intended, while it's not considering the edge cases.
The only way you can achieve what you want is by using multiple ifs, or by redesigning your application.

Answer 2

When the url is index.php?, or index.php, "test0" is shown.
Why is this? The condition is not met, so should the default not be shown?
Like a good question, your question as well contains the answer already.
You already have realized that the condition must be met even you think it is not met. Therefore you ask. So let's see which condition is met:
case isset($_GET['test0']):
echo "test0<br>";
break;
This is a test for isset($_GET['test0']) and we know with the request that this is FALSE. So this test tests for FALSE.
Now let's see against what this tests:
switch ($_SERVER['QUERY_STRING']) {
That is $_SERVER['QUERY_STRING']. So if $_SERVER['QUERY_STRING'] is FALSE the test0 will be output.
Because switch { case:} in PHP does loose comparison, the empty string $_SERVER['QUERY_STRING'] is FALSE. This is why you see the output.
Easy if you know why, right? And all so logical.
And what you wanted to test against was not $_SERVER['QUERY_STRING'] but just TRUE:
switch (TRUE)
{
case isset($_GET['test0']) :
...
}

Answer 3

This gets the job done, too.
<?php
$q = $_SERVER['QUERY_STRING'];
if(!empty($q) && isset($q) && strlen($q) >0 ){
$url = $q;
switch ($url){
case true;
echo $url;
break;
}
}
else {
echo "no test<br>";
}

Answer 4

what about
$found = false;
for($i=0;$i <=4; $i++){
if( isset($_GET['test'.$i]) ){
echo "test".$i;
$found = true;
}
}
if(!$found){
echo "no test";
}