Rotating code

[LeeUK]

I have a site that I run with 2 other people & we each have a google adsense account to help pay for the site. I want to be able to rotate our codes so that each of our ads appear evenly.

I have made a constants.php page & put the three codes as constants like this

define (USER1, '<script>a bunch of code here</script>');
define (USER2, '<script>a bunch of code here</script>');
define (USER2, '<script>a bunch of code here</script>');

Then I have called for constants.php in all pages, and I am manually rotating them every other day.
Is there a piece of code that I can enter on the main pages that will auto rotate them? or is it a little more complicated & I should get a programmer?

Thanks.

[TheMadMidget]

This will rotate on each visit. Make sure you have the "hits.txt" file writtable. This is based off a counter and will still give you a counter, but hidden.
To add or remove user/accounts, just change the $numberOfAccoun ts and make or delete another "case:" structure.
[PHP]
$hitslog = "hits.txt"; # Path to the hits file, leave alone if in the same directory
$hits = file($hitslog);
$hits = $hits[0] + 1;

## Opening the hits file and write the number of hits:
$fp = fopen($hitslog, "w");
fwrite($fp, $hits);
$numberOfAccoun ts = 3;
$account = ($hits % $numberOfAccoun ts) + 1;

switch ($account) {
case 1:
echo "<script>Us er1</script>";
break;
case 2:
echo "<script>Us er2</script>";
break;
case 3:
echo "<script>Us er3</script>";
break;
}
[/PHP]