$session data returns only 0 - php

Question

I'm trying to put a script together that will do some math for the user.
That works fine however when i try to put it in a session and try to show the value to the user it will only return 0 if its set to 0.
Does anybody know where i did wrong?
<?php
session_start();
if( isset( $_SERVER['HTTP_X_REQUESTED_WITH'] ) ){
$class1 = filter_var($_POST['class1'], FILTER_SANITIZE_STRING);
$class2 = filter_var($_POST['class2'], FILTER_SANITIZE_STRING);
$class3 = filter_var($_POST['class3'], FILTER_SANITIZE_STRING);
$class4 = filter_var($_POST['class4'], FILTER_SANITIZE_STRING);
$class5 = filter_var($_POST['class5'], FILTER_SANITIZE_STRING);
$class1C = $class1 * 35;
$class2C = $class2 * 5;
$class3C = $class3 * 7.5;
$class4C = $class4 * 26;
$class5C = $class5 * 2.5;
$totaal1 = $class1C + $class2C + $class3C + $class4C + $class5C;
$res = array($class1C, $class2C, $class3C, $class4C, $class5C, $totaal1);
foreach($res as $name => $var) {
$_SESSION[$name] = $var;
}
$result = array("error" => false, "html" => null);
$result["error"] = false;
$result["html"] = "<h3>Session information: var_dump($_SESSION[$class1C]) ($_SESSION[$class2C]) ($_SESSION[$totaal1])</h3>";
} else {
$result["error"] = true;
$result["html"] = "<h3>Error</h3>";
}
echo json_encode($result);
exit;
?>

Answer 1

You cannot call var_dump inside the double quoted string, and var_dump does not return anything: it only display things.
Even if you could, $class1C is not a valid index for $_SESSION
Keeping the same logic as your code, you may change your line to the following:
$result["html"] = "<h3>Session information:";
ob_start();
var_dump($_SESSION[0]); // contains $class1C
echo $_SESSION[1]; // contains $class2C
echo $_SESSION[5]; // contains $totaal1
$result["html"] .= ob_get_clean();
$result["html"] .= "</h3>";
EDIT:
If you want to use the indexes 'class2C', 'totaal1' etc.. you need to init $res as follow:
$res = array(
'class1C' => $class1C,
'class2C' => $class2C,
'class3C' => $class3C,
'class4C' => $class4C,
'class5C' => $class5C,
'totaal1' => $totaal1
);
Then, your loop to set $_SESSION will set correct indexes, and you will be able to use $_SESSION['class1C'] to get proper values.