controller

<?php
defined('BASEPATH') OR exit('No direct script access allowed');

class Main extends CI_Controller {

    public function __construct()
    {
        // You need to load your model before you can use it.
        $this->load->model('users_model');
    }

    public function index(){

        $this->load->view('login');
    }

    public function get_login() {
        // Great! You're using the input library as it is meant to be used!
        $user = $this->input->post('txtuser');
        $pass = $this->input->post('txtpass');

        $user = $this->users_model->login($user,$pass);

        $valid_positions = array('1','2','3','4','5');

        if($user->num_rows() > 0 ) {
            $row = $user->row();

            $fullname = $row->firstname . '' . $row->lastname;
            $username = $row->username;
            $dateAdded = $row->dateAdded;
            $this->session->set_userdata('fullname', $fullname);
            $this->session->set_userdata('username',$username);
            $this->session->set_userdata('dateAdded',$dateAdded);

            if(in_array($row->positionID, $valid_positions)) {
                $data['success'] = $row->positionID;
            } else {
                $data['success'] = '0';
            }

        generate_json($data);
    }

    public function logout() {
        $this->load->view('login');
    }
}