Split Testing - Prosper Script

<?

//Tracking202 Offer Rotation Script

//enter your affiliate urls below, you can enter as many as you want, please
//make sure that you have the affiliate url with the SUBID syntax at the end
//of it, for reference goto: subids.com for more information.
$offer[1] = 'http://myaffiliateurl.com?subid=';
$offer[2] = 'http://myaffiliateurl2.com?subid=';
$offer[3] = 'http://myaffiliateurl3.com?subid=';

//this is the text file, which will be stored in the same directory as this file, 
//count.txt needs to be CHMOD to 777, full privlledges, to read and write to it.
$myFile = "count.txt";

//open the txt file
$fh = @fopen($myFile, 'r');
$offerNumber = @fread($fh, 5);
@fclose($fh);

//see which landing page is next in line to be shown.
if ($offerNumber >= count($offer)) {
    $offerNumber = 1;
} else {
    $offerNumber = $offerNumber + 1;
}

//write to the txt file.
$fh = fopen($myFile, 'w') or die("can't open file");
$stringData = $offerNumber . "\n";
fwrite($fh, $stringData);
fclose($fh);

//grab the subid that t202 adds
$subid = $_GET['subid'];

//redirect to the affilate url, + add the subid at the end
header('location: ' .$offer[$offerNumber] . $subid); 

?>