Hi I am have a single image upload script it works when add the action into a different file but when I try to add the whole script in a single file the php doesnt run?

PHP Code:
<form action="<?php echo $_SERVER["PHP_SELF"?>" method="post" enctype="multipart/form-data">
   <p>
      <label for="file">Select a file:</label>
       <input type="file" name="userfile" id="file"> <br />
      <input type="submit" value="upload">
   <p>
</form>


<?php
if (isset ($_POST["submit"])) {
   
// Configuration - Your Options
      
$allowed_filetypes = array('.jpg','.gif','.bmp','.png'); // These will be the types of file that will pass the validation.
      
$max_filesize 524288// Maximum filesize in BYTES (currently 0.5MB).
      
$upload_path './images/'// The place the files will be uploaded to (currently a 'files' directory).
 
   
$filename $_FILES["userfile"]["name"]; // Get the name of the file (including file extension).
   
$ext substr($filenamestrpos($filename,'.'), strlen($filename)-1); // Get the extension from the filename.
 
   // Check if the filetype is allowed, if not DIE and inform the user.
   
if(!in_array($ext,$allowed_filetypes))
      die(
'The file you attempted to upload is not allowed.');
 
   
// Now check the filesize, if it is too large then DIE and inform the user.
   
if(filesize($_FILES["userfile"]["tmp_name"]) > $max_filesize)
      die(
'The file you attempted to upload is too large.');
 
   
// Check if we can upload to the specified path, if not DIE and inform the user.
   
if(!is_writable($upload_path))
      die(
'You cannot upload to the specified directory, please CHMOD it to 777.');
      
      
      
      
    
$filename time().$ext// this will give the file current time so avoid files having the same name
   // Upload the file to your specified path.
   
if(move_uploaded_file($_FILES["userfile"]["tmp_name"],$upload_path $filename))
         echo 
time(). ' Your file upload was successful, view the file <a href="' $upload_path $filename '" title="Your File">here</a>'// It worked.
      
else
         echo 
'There was an error during the file upload.  Please try again.'// It failed :(.
}
?>