How to Add An Active Class to PHP Pagination

How to Add An Active Class to PHP Pagination

[photoinshot]

After working with your code in the previous two videos then adding the active class as you showed in this video, I noticed an error that occurs. When the page first loads and there is no get variable in the url you get this error: Warning: Undefined array key "page".
I fixed it by doing this:
for($page=1; $page<=$number_of_pages; $page++){
if (isset ($_GET['page'])) {
if ($_GET['page'] == $page) {
$active ="active";
} else{
$active ="";
}
}

if (isset($active)) {
echo '<a class="'.$active.'" >'.$page.'</a>';
}else{
echo '<a >'.$page.'</a>';
}}

Not sure if this is the best way as I am just learning php and coding, I would be very interested to see how you would do it. Or have I missed something?