Alphanumeric Upload Sorting

This is what the script does: when a file is uploaded from a form, this script checks
what directory it should go into. So before the upload occurs, the alphanumeric
directories are created ( only once, of course). Here it is in code (Please note that this just example code):

UPLOAD.PHP<?phpecho "<form action='upload-sort.php' method='get' enctype='multipart/form-data'>";echo "Upload a file: <input type='file' name='upload'>";echo "</form>";?>UPLOAD-SORT.PHP<?php$alphaNum = ('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 0, 1, 2, 3, 4, 5, 6, 7, 8, 9);$arraySize = count($alphaNum);for($n=0; $n<$arraySize; $n++){     if(!directory_exists($alphaNum[$n])) mkdir($alphaNum[$n]);     if(substr($_FILES['upload']['name'], -4) != ".exe")     {          if(substr($_FILES['upload']['name'], 1) == $alphaNum[$n])          copy($_FILES['upload']['tmp_name'], $_FILES['upload']['name']);     }}?>

I'm hoping that the $_FILES array works. If you have any trouble with that variable, use the $HTTP_POST_FILES instead and see if it works. If it doesn't, come back here and I'll correct that problem.