Php session issues?

This is my first time using sessions, and I think I'm using them wrong. I had a page executing fine with normal variables which retrieved user submitted post data, but, I had to convert those into session variables so peoples information got assigned UIDs and didn't get mixed up. However, when I ran the page with the session variables, it didn't execute, it was just blank. I've looked over my code, and I don't see any syntax errors, so i guess I have a fundamental problem with using session variables. Below is some code which I think has problems, so, please in your answer, tell me what you think is wrong, and some common restrictions of session variables.

below, I converted a $set1 variable into a session variable, receiving the data, i don't know if this is correct.
$_SESSION['set1'] = $_POST['set1'] ;

I'm not sure if this is correct either...
if ($_SESSION['set1'] == $getvalue1)...

I strung these together, not sure if this can work
$_SESSION['cumulative'] = $_SESSION['score1'] + $_SESSION['score2'] ;

or this...
$_SESSION['score'] = ($_SESSION['cumulative'] / $divisor)*100 ;

thanks for your input :)

First, check your web server logs for error. Make sure php error reporting is on. Whenever you get a blank page, you've got an error.

Are you calling session_start(); at the top of each of your files? Presuming you have a form that is posting 'set1' to the file in which you are setting the session variable, your syntax seems to be okay...

Edit: If you have server access, the apache logs are usually someplace like /usr/local/apache/logs. If you stick a file containing the following code in your webroot, it will tell you where logs, config files, etc. reside -

<?php
phpinfo();
?>

Also, try putting error_reporting(E_ALL); at the top of your php files. It should cause errors to go to the browser.

http://us2.php.net/error_reporting

If all else fails, go with brute-force - add a few echo statements through your code to see how far it's getting before it bails out.

One problem you are having is that if you have not enabled session autostarts in your php.ini file, you must call session_start() at the very top of any page on which you intend to use server variables.

http://us3.php.net/manual/en/function.se...
http://us3.php.net/manual/en/ref.session...

You can assign superglobals back and forth as you have above:

$_SESSION['set1'] = $_POST['set1'] ; // this is fine

You can also assign any local variable to the session superglobal, as below:

$foo = "bar";
$_SESSION['foobar'] = $foo;
echo $_SESSION['foobar']; //prints "bar"

Session variables can hold objects and primitive data types (strings / numbers / booleans, etc.), unless you are using session autostarts, in which case a session can only contain primitives.

As such, if your session variable contains a primitive, you can work with the primative as you would a local variable, including doing math on them.