Strings willen niet aan elkaar

<?php

   //configuration settings
   //you can change the upload directory to any existing directory
   $plek = $_POST['album'];
   $path = $_SERVER['DOCUMENT_ROOT'].'/fotoalbum/';
   
$upload_directory = $path.$plek;
   mkdir($path.$plek,0777);

   
   //change the maximum number of uploads
   $max_uploads = 20;



   if ($_SERVER['REQUEST_METHOD'] == 'POST')
   {
      //create file fields to select the files you would like to upload
      if ($_POST['files'])
      {
         printf('<form method="post" action="%s" enctype="multipart/form-data">', $_SERVER['PHP_SELF']);
         //create list with the file fields
         for ($i = 1; $i <= $_POST['files']; $i++)
         {
            printf('<input type="file" name="file_%s" size="100"><br />', $i);
         }
         printf('<input type="button" onclick="javascript: history.back(-1);" value="Cancel">');
         printf('<input type="submit" value="Upload files">');
         printf('<input type="hidden" name="history_files" value="%s">', $_POST['files']);
         printf('</form>');
      }
      else
      {
         //upload all files and create report
         printf('<h3>Result report:</h3>');
         printf('Upload to: %s<br /><br />', $upload_directory);
         printf('<table border="1">');
         for ($i = 1; $i <= $_POST['history_files']; $i++)
         {
            $tmp_filename = $_FILES['file_'.$i]['tmp_name'];
            $filename = $_FILES['file_'.$i]['name'];
            if (move_uploaded_file($tmp_filename, $upload_directory.'/'.$filename))
            {
               $status = 'Done...';
            }
            else
            {
               $status = 'Failure!';
            }
            printf('<tr><td>%s</td><td>%s</td><td>%s</td></tr>', $i, ($filename)?$filename:'&nbsp;', $status);
         }
         printf('</table>');
      }
   }
   else
   {
      printf('<form method="post" action="%s">', $_SERVER['PHP_SELF']);
      printf('Van wie zijn de fotos?');
      printf('<input type="text" name="album">');
      printf('Number of files to upload: ');
      printf('<select name="files">');
      //create list with numbers
      for ($i = 1; $i <= $max_uploads; $i++)
      {
         printf('<option value="%1$s">%1$s', $i);
      }
      printf('</select> ');
      printf('<input type="submit" value="Create fields">');
      printf('</form>');
   }

?>