Initials avatar logged in

<?php if (is_user_logged_in()){ ?>

<?php global $current_user;
wp_get_current_user();
$a = $current_user->user_firstname . "\n";
$b = $current_user->user_lastname . "\n";
?>

<a class="ava-log" href="/my-account" target="_self">
<?php
echo $a[0]; 
echo $b[0]; 
?>
</a> 


<?php } else { ?>

<a class="btn-log" style='display:none' href="/log-in">
<i class="fal fa-user bl-ico"></i>
</a>

<?php }; ?>