Tjek om felt er udfyldt

Kode 

<form name="form1" enctype="multipart/form-data" method="post" action="processFiles.php">
  <p>
  <?
  // start of dynamic form
  $uploadNeed = 10;
  for($x=0;$x<$uploadNeed;$x++){
  ?>
       <input name="uploadFile<? echo $x;?>" type="file" id="uploadFile<? echo $x;?>">

  </p>
  <?
  // end of for loop
  }
  ?>
  <p><input name="uploadNeed" type="hidden" value="<? echo $uploadNeed;?>">
    <input type="submit" name="Submit" value="Submit">
  </p>
</form>