Not understanding how to add cart into PHP - php

Question

I am stuck on this code. I am making a web page and on the side there is a place for a cart. And with the you should be able to click on an item and add it to cart. Well I am having trouble getting it to add it to cart. Can someone help me understand what I should be doing. I have been working on it for a few days and no matter what I am doing nothing is working. If i get the code to show you have 0 in your cart it wont add anything if i try to put it in the cart.
<h1>Cart Contents?</h1>
<div class="p2">
<?php
// Get all the categories and
// link them to category.php.
// Define and execute the query:
$q = 'SELECT category_id, category FROM categories ORDER BY category';
$r = mysqli_query($dbc, $q);
// Fetch the results:
while (list($fcid, $fcat) = mysqli_fetch_array($r, MYSQLI_NUM)) {
// Print as a list item.
echo "<li>$fcat</li>\n";
if($_SERVER['PHP_SELF']!="CART FILE"){
echo "<h1>Cart Contents</h1>";
echo "<div class=\"p2\">";
$itemCount=X;
foreach($_SESSION['cart'] as X=>X){
for($i=0;$i<count(X);$i++){
$itemCount+=X;
}
}
echo "You have ".$itemCount." total items in your cart.";
echo "</div>\n";
} // End of while loop.
?>
<h1>Specials?</h1>
<div class="p2">
<p>Maybe place specials or new items or related items here.</p>
</div>
</div>
<div class="content">
Ok here is a link to what the cart should do if you look over to the side it should do what that one is doing.
http://www.programmerskit.com/advPHP/ch5/

Answer 1

Shouldn't
$itemCount=X;
foreach($_SESSION['cart'] as X=>X){
for($i=0;$i<count(X);$i++){
$itemCount+=X;
}
}
just be:
$itemCount = count($_SESSION['cart']);
I can't otherwise figure out what that code is supposed to be doing.
Also, that code that outputs the cart appears to be in a while loop outputting each item category, so you will be displaying the cart multiple times, which I can only assume is not desired functionality.
Also, another poster made a point about the invalid use of X as a constant, which is also a good point.

Answer 2

You've got a bare X used all over the place. While saying
$somevar = X;
would be legitimate if you'd already done define('X', 'somevalue') previously, this next one
foreach($_SESSION['cart'] as X=>X){
is completely invalid. You cannot assign new values to a defined constant, let alone try to assign TWO different values at the same time
foreach($_SESSION['cart'] as $key => $value)
is how that particular bit of code should be.