The answer in your link is correct. If it’s just showing PHP code then your code isn’t between PHP tags <?php & ?>.
<?php if (!is_user_logged_in()) :?>
<a href="https://wordpress.stackexchange.com/member-login/" class="login">Member Login</a>
<?php else : ?>
<a href="http://wordpress.stackexchange.com/account-page/" class="login">Welcome <?php echo $current_user->display_name; ?></a>
<?php endif; ?>
<a href="http://wordpress.stackexchange.com/membership/join-sccap-renew-membership/" class="join">Join</a>