Run controller from an external site

I have the following problem / question:

I have Wordpress installed and CodeIgniter also. In CodeIgniter I have to do a function that adds +1 in the database when a category is seen in wordpress . Then the following code inside a controller of codeigniter

<?php
function add($id){

$this->db->where('id', $id);
$banner = $this->db->get('banners')->row();
$add = $banner->views + 1;

$this->db->where('id', $id);
$this->db->update('banners', array('views'=>$add));

return true;
?>

I need to run this code every time someone goes into a category of wordpress . I thought about doing file_get_contents() but I do not know if it will work because it takes the contents of a link. I wanted to know how I can do it. The file of wordpress related to categories I already know, the problem is only in making / using a function to execute when entering or updating the page, because I want to make a banner display system.