nogeens

if (isset($_POST['submit'])) {
					$studentnummer = $_SESSION['studentnummer'];

					$cat11 = $_POST['katogorie1'];
					$cat22 = $_POST['katogorie2'];
					$cat33 = $_POST['katogorie3'];
					$cat44 = $_POST['katogorie4'];
					if($cat11 == '' & $cat22 == '' && $cat33 == '' && $cat44 == ''){
						echo "Vul voor elke catogorie een klas in!";

					}else{

						$db = new PDO('mysql:host=localhost;dbname=onething', 'root', '');
						$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);


						$katogorie1=$_POST['katogorie1'];
						$katogorie2=$_POST['katogorie2'];
						$katogorie3=$_POST['katogorie3'];
						$katogorie4=$_POST['katogorie4'];

						$addvalue1 = "groepje" . $katogorie1;
						$addvalue2 = "groepje" . $katogorie2;
						$addvalue3 = "groepje" . $katogorie3;
						$addvalue4 = "groepje" . $katogorie4;
						echo "<br><br>";


						if($db === false){
							echo "Connection Error";
						}else{

						}
						try {
						$update = "UPDATE cat1 SET stemmen = stemmen + 1 WHERE groepjes = '$addvalue1'";
						$update1 = "UPDATE cat2 SET stemmen = stemmen + 1 WHERE groepjes = '$addvalue2'";
						$update2 = "UPDATE cat3 SET stemmen = stemmen + 1 WHERE groepjes = '$addvalue3'";
						$update3 = "UPDATE cat4 SET stemmen = stemmen + 1 WHERE groepjes = '$addvalue4'";
						$update4 = "UPDATE studenten SET ingelogd = 1 WHERE studentennummer = '$studentnummer'";





						    }
						catch(PDOException $e)
						    {
						    echo $update . "<br>" . $e->getMessage();
						    echo $update1 . "<br>" . $e->getMessage();
						    echo $update2 . "<br>" . $e->getMessage();
						    echo $update3 . "<br>" . $e->getMessage();
						    echo $update4 . "<br>" . $e->getMessage();
						    }

						    $db->exec($update);
						    $db->exec($update1);
						    $db->exec($update2);
						    $db->exec($update3);
						    $db->exec($update4);

						    echo "New record created successfully"; //-weghalen!

						    $select = "SELECT SUM(ingelogd) AS sum FROM studenten";
						    $query = $db->query($select);
						    $sum_row = $query->fetch(PDO::FETCH_ASSOC);
						    $sum = $sum_row['sum'];
						    echo "<br>";