Need a help with simple problem

Well I’ve just recently started my blog, as in yesterday. First of all I’m a complete newbie. I know like core basics but other then that it all just goes over the head. Anyway here is my simple newbie question…. I’m trying to combine these to tags into one <li> tag.

<li class="<?php echo $oddcomment; ?>"
 id="comment-<?php comment_ID() ?>">

<li class="comment <?php
    echo (is_wpuser_comment() ? ' commentOfficialUser' : '');
  ?>">

I just don’t know how to have two different values in the class attribute or it’s just so late I’m way too tired.

Thank you for your valued input.