to form div with while loop

<?php
$array = explode(',',$arr['amenity_id']);
$ame=mysql_query("select * from `amenity`");
$i=0;
while($a=mysql_fetch_array($ame))
{
if($i==0)
{
echo '<div class="col-lg-4 col-md-6 col-sm-12">';
}
$i++;

if(in_array($a['amenity_id'], $array )){
?>
<label class="checkbox"><input type="checkbox" name='amenities[]' value="<?=$a['amenity_id']?>" checked><?=$a['amenity_name']?></label>
<?php }
else{ ?>
<label class="checkbox"><input type="checkbox" class="checkbox" name='amenities[]' value="<?=$a['amenity_id']?>" ><?=$a['amenity_name']?></label>
<?php }
if($i==3){ echo '</div>'; $i=0;}
}

?>