Current page and 'active' class in menu

uri->segment returns only one segment. Segments are split by slashes. So it can't be 'main/index'. One segment is either 'main' or 'index'. If you have all stuff in one controller, you don't really need controller check, so use just the second segment, like

PHP Code:

<?=($this->uri->segment(2)==='index')?'active':''?>

You can also use router->fetch_method instead, which is more reliable as it is less prone to errors caused by changes in urls, routing config and/or .htaccess