Checkbox tableau

<?php
$problems = !empty($_POST['problem']) ? $_POST['problem']: array();
?>
<form name='test' action='' method='POST'>
 <pre>
 <input type='checkbox' value='toto' name='problem[]' <?php if (in_array("toto", $problems)) { echo " checked='checked' ";} ?> >toto
 <input type='checkbox' value='titi' name='problem[]' <?php if (in_array("titi", $problems)) { echo " checked='checked' ";} ?> >titi
 <input type='checkbox' value='tutu' name='problem[]' <?php if (in_array("tutu", $problems)) { echo " checked='checked' ";} ?> >tutu
 </pre>	 
	<input type='submit' value='valider'>
</form>	>