PHP isset equal $var1 or $var2 - php

Question

I'm trying to make routing system.
What I want to do:
Url: http://localhost/wiki.php?post_id=1 invoke second if
Url's: http://localhost/wiki.php?post_id=1&action=upvote
http://localhost/wiki.php?post_id=1&action=downvote invoke first if
This is routing system:
if(isset($_GET['post_id']) & ((isset($_GET['action']) ? $_GET['action'] : null) == "upvote" || "downvote")){
//Do stuff
}else if(isset($_GET['post_id'])){
//Do stuff
}
Problem:
Url's: http://localhost/wiki.php?post_id=1&action=upvote http://localhost/wiki.php?post_id=1&action=downvote work like they are supposed to.
But url: http://localhost/wiki.php?post_id=1 invokes first not second if too...
Notice: Undefined index: action in D:\xampp\htdocs\controllers\WikiController.php on line 18
Line 18: $rate = $_GET['action']; it's inside in first if.
While testing I figured out that if I change if(isset($_GET['post_id']) & ((isset($_GET['action']) ? $_GET['action'] : null) == "upvote" || "downvote")){
too
if(isset($_GET['post_id']) & ((isset($_GET['action']) ? $_GET['action'] : null) == "upvote")){
or
if(isset($_GET['post_id']) & ((isset($_GET['action']) ? $_GET['action'] : null) == "downvote")){
It works fine. But I want to learn how to do this right, not just simply made 2 different routers.

Answer 1

this part (exp) == "upvote" || "downvote" does not work like you suppose it does. It only tests if exp is equal to "upvote", the second part "downvote" is understood as a boolean which is true, so you stay in the first part of the alternative..
try with
if(isset($_GET['post_id']) && (($exp = (isset($_GET['action']) ? $_GET['action'] : null)) == "upvote" || $exp == "downvote")){

Answer 2

For clarification, a single (ampersand) & is "bitwise":
http://php.net/manual/en/language.operators.bitwise.php
Therefore, you need to change your & to &&.
From the manual:
$a & $b And Bits that are set in both $a and $b are set.
What you're after is the logical && operator:
http://php.net/manual/en/language.operators.logical.php
$a && $b And TRUE if both $a and $b are TRUE.

Answer 3

|| "downvote" will always return true since you're not comparing it to anything. You have to add (isset($_GET['action']) ? $_GET['action'] : null) == in front of that string too.
So your statement would be:
if(isset($_GET['post_id']) && ((isset($_GET['action']) ? $_GET['action'] : null) == "upvote" || (isset($_GET['action']) ? $_GET['action'] : null) == "downvote")){
//Do stuff
}else if(isset($_GET['post_id'])){
//Do stuff
}

Answer 4

$routes = [
'upvote','downvote'
];
if(isset($_GET['post_id']) && isset($_GET['action']) && in_array($_GET['action'],$routes)){
echo 'running if';
}else if(isset($_GET['post_id'])){
echo 'running else if';
}
You are missing && was the problem, i just change this for dynamic route if you need to change in future!