Need help with checking current page

Hi

I need some help please, I’m not very familiar with php.

How would you check something like the following code dynamically?

if ( is_page('home') ) { do something }
elseif ( is_page('about') ) { do something }
...

I’m trying to add css class to the actual links for the nav menu, I found this code which works lovely

function add_nav_class($output) {
$output= preg_replace('/<a/', '<a class="your-class"', $output, -1);
return $output;
}
add_filter('wp_nav_menu', 'add_nav_class');

but I need to do something like this, which has a different class if you are on that page.

function add_nav_class($output) {
if (is_page(WHAT_GOES_HERE?)) { $menuclass = '<a class="menuOn"'; }
else { $menuclass = '<a class="menuOff"'; }

$output= preg_replace('/<a/', $menuclass, $output, -1);
return $output;
}
add_filter('wp_nav_menu', 'add_nav_class');

hope that makes sense..
many thanks!