How to create categories and associate them with posts

I'm doing some tests, like counting how many posts are in a category. Unfortunately I can not get it running because it tells me it can not pick up the variable, but if I do "echo" me it prints correctly.

Anyway, I cleaned up everything and now only show all the results in the "love" category. How can I make the variable of all categories in place?

Controller:

PHP Code:

public function category($slug_category) {
        $this->load->view('post/category');
    } 


Model

PHP Code:

public function countPostCat() {
        $this->db->like('id');
        $this->db->from('post');
        $this->db->where('slug_category', 'love');
        return $this->db->count_all_results();
    } 


Views

PHP Code:

(<?php echo $this->admin_model->countPostCat(); ?>)