PHP - How to add up points from a specific value only - php

Question

I want to add up points from the "vak" which is "wiskunde" if the box "vak" is filled with something else than the afformentioned "vak" "wiskunde" it doesnt need to be added up.
pastebin code ugwwDda8
<?php
if($_GET);
{
$jp = $_GET["janpunten"];
$pp = $_GET["pietpunten"];
$kp = $_GET["klaaspunten"];
$janvak = "";
$pietvak = "";
$klaasvak = "";
$totaal = "0";
if ( $janvak && $pietvak && $klaasvak = "Wiskunde" ) {
$totaal = $jp + $pp + $kp;
}
}
?>
So for example, the logic here would be if $janvak $pietvak $klaasvak are all wiskunde, they would add up all the points, but if only $janvak and $pietvak were wiskunde, it would only add up the points from those two.

Answer 1

This doesn't do what you probably think it does:
if ( $janvak && $pietvak && $klaasvak = "Wiskunde" )
This may make sense linguistically when spoken aloud in human languages, but computers don't have human intuition. Each part between the && operators is its own distinct boolean operation. So it's equivalent to this:
if ( ($janvak) && ($pietvak) && ($klaasvak = "Wiskunde") )
There's a pretty good chance that all three of these will always be true. (Or perhaps the first two will always be false? Since they're just empty strings. Either way, the code isn't doing what you want it to do.)
Additionally, you're using the assignment operator (=) instead of the comparison operator (==), so that will also always be true and will modify that variable when performing the if check.
It looks like what you wanted was this:
if ( $janvak == "Wiskunde" && $pietvak == "Wiskunde" && $klaasvak == "Wiskunde" )
When chaining together any combination of boolean logic operations, always make sure that each individual operation is a complete and distinct component of the overall logic.