PHP Code. This is the index.php file. The comments are work to be done:

$//$ which is saved in the session.

$//$ if there is a key named "item" in the query string...

if $($isset$($$$\_$GET$[\text{'}$item$\text{'}]))\{$

$//$ get the cart from the session $($or create it$)$

if $($isset $($$$\_$SESSION$[\text{'}$cart$\text{'}]))($

$cart $=$ $$\_$SESSION$[[$cart$"]$;

$\}$ else $\{$

$cart $=$array$()$;

$\}$

$//$ use the append operator to append the value of the item to the array

$cart$[]=$ $GET$[\text{'}$item$\text{'}]$;

$//$ if our array grows too large, php may move it to another location

$//$ in memory, so save the cart's address back into the session

$$\_$SESSION$[[$cart$\text{'}]=$ $cart;

$\}$

$?>$

DOCTYPE html$>$

$$ htmls

$$ head $>$

TODO: prevent the WARNING caused when $we$ don't yet have a cart$\frac{?}{\frac{?}{?}}$

$(e.g.,$ when the page first loads into the browser$)\frac{?}{\frac{?}{?}}$

display the cart contents

foreach $($$cart $as$ $thing$)\{$

echo $thing $.""$;

$\}$

$?>$

body $>$

$html>$