The assignment only involves introducing the student to using cookies and a session cookie is used in the exercise, though the student could choose to add an expiration if they desired.

The html code was not included because it was not necessary. The form only passes one variable via post from a selection of items displayed with a radio button, so only one item can be selected at a time. The user then uses their back button to select another item and submit it to the script.

I know there are better ways to write the script but this is only to be a basic exercise.

If you look at the code above, the order events is:

1. declare variables
2. assign input item to variable
3. retrieving cookie
4. adding purchase to cookie
5. create cookie

Now, logically, it would make sense that you would create the cookie first before retrieving it. But, if we put the code to the create cookie before the code to retrieve the cookie, the script only displays the item currently selected from the form. If we use the code as is, the item selected is kept in a session cookie and is printed out as well as other items selected when we use the back button to select another item.

So, the question is, when a person uses the form for the very first time, there is no session cookie because it hasn't been created. Yet the code only works if we "retrieve" the cookie and then create it.

Any ideas as to why it works this way?

Don't think in terms of "the cookie" - that obscures what is really going on. Think in terms of a) a cookie FILE - a file on a user's disk, b) a cookie VARIABLE - a temporary value in your script, c) a cookie HEADER - text instructions sent along with the HTML page from your script to the user's browser. The steps now become:

1. Check to see if there is a previously created COOKIE FILE. If so, put the items stored there in @purchases, otherwise leave @purchases empty.

2. Add the current purchase to @purchases.

3. Create a new COOKIE VARIABLE, $C_records, and store the value of @purchases there.

4. Print the new cookie variable as a COOKIE HEADER.

5. When the browser reads the COOKIE HEADER, it will create a new COOKIE FILE. This file will either replace the old previously created cookie file if it exists, or will be created as a completely new file.

Why should you check for a pre-existing COOKIE FILE before creating a new COOKIE VARIABLE? Because your script has no way of knowing whether this is the first item the user is purchasing or the tenth item. If it is the first item, checking for the COOKIE FILE will simply not find anything and the new COOKIE VARIABLE will be created entirely from the user's current purchases. If it is the second, or third, or tentch item the user is purchasing, checking for the COOKIE FILE will find the previous purchases and add them to the current purchase so that when you create a new COOKIE VARIABLE, that variable will contain both current and previous purchases.