I got this error undefined index. normally i know how to solve those errors except this one: looks like I forgot something somewhere???
<?php
session_start();
include 'dbcon.php';
$page = 'index.php';
if(isset($_GET['toevoegen'])){
$query ='SELECT partnr, hoeveelheid FROM producten WHERE partnr='.mysqli_real_escape_string($connectie,(int)$_GET['toevoegen']);
$result = mysqli_query($connectie, $query);
while($result_row = mysqli_fetch_assoc($result)){
if($result_row['hoeveelheid']!=$_SESSION['winkelwagen_'.$_GET['toevoegen']]){
$_SESSION['winkelwagen_'.$_GET['toevoegen']]+='1';
}
}
}
?>