Register.php

<?php
ini_set('error_reporting', ~E_NOTICE);

class Register extends CI_Controller {
  function __Construct(){
      parent::__Construct();
      $this->load->database(); // load database
      $this->load->model('User_Info_Model'); // load model
      $this->load->helper('url');
      //$this->output->enable_profiler(TRUE);
      session_start();
  }

  public function index(){

    $this->load->helper(array('form', 'url'));
    $this->load->library('form_validation');

    $this->form_validation->set_rules('firstname', 'First Name', 'required');
    $this->form_validation->set_rules('lastname', 'Last Name', 'required');
    $this->form_validation->set_rules('location', 'Location', 'required');
    $this->form_validation->set_rules('email', 'Email', 'required');
    $this->form_validation->set_rules('username', 'Username', 'required');
    $this->form_validation->set_rules('password', 'Password', 'required',
            array('required' => 'You must provide a %s.'));
    $this->form_validation->set_rules('email', 'Email', 'required|valid_email');

    if ($this->form_validation->run() == FALSE){
        $this->load->view('templates/header');
        $this->load->view('register');
    }

    // load the homepage once properly submitted
    // https://www.codeigniter.com/user_guide/libraries/form_validation.html#callbacks-your-own-validation-methods

    // add user to db, launch session, send to home

    else {
      //add user to db
      $user = $this->User_Info_Model->addUser();

      $data['user'] = $user;
      //get user id, launch session, send to home
      if($user !== []){
        $this->session->set_userdata($user);
        $data = $this->session->all_userdata();

        //$this->load->view('login', $data);
        redirect('/All_Tweets');
      }
      // if no, refresh register
      else {
        $this->load->view('templates/header');
        $this->load->view('register', $data);
      }

    }

  }
}