class Signin extends CI_Controller {

  public function __construct()
  {
    parent::__construct();
  }

  public function index()
  {
    $this->load->view('signin');
  }

  public function signin()
  {
    $this->form_validation->set_rules('email', 'Email', 'required|trim|valid_email');
    $this->form_validation->set_rules('password', 'Password', 'required');
    $this->form_validation->set_error_delimiters('<p class="error">', '</p>');
    if ($this->form_validation->run())
    {
      $email = $this->input->post('email');
      $password = $this->input->post('password');
      $this->load->model('Usermodel');
      $current_user = $this->Usermodel->user_login($email, $password);
      // Unset the current user's data
      if ($current_user) {
       $this->session->set_userdata(
         array(
          'user_id' => $current_user->id,
          'user_email' => $current_user->email,
          'user_first_name' => $current_user->fname,
          'is_logged_in' => TRUE
          )
         );
       redirect('home');
     } else {
        $this->session->set_flashdata("signin_failure", "Incorrect email or password");
        redirect('signin');
      }
    }
    else
    {
     $this->load->view('signin');
   }
  }

  public function signout(){
    // Unset the current user's data
    $this->session->unset_userdata('user_id');
    $this->session->unset_userdata('user_email');
    $this->session->unset_userdata('user_first_name');
    $this->session->unset_userdata('is_logged_in');

    // Load the signin view
    $this->load->view('signin');
  }
}

<div id="navbar" class="collapse navbar-collapse">
    <ul class="nav navbar-nav navbar-right">
      <?php if($this->session->userdata('is_logged_in')) : ?>
      <li class="dropdown">
        <a class="dropdown-toggle" data-toggle="dropdown" href="#"><span class="glyphicon glyphicon-user"></span> Welcome, <?php echo $this->session->userdata('user_first_name'); ?>
        <span class="caret"></span></a>
        </a>
        <ul class="dropdown-menu">
          <li><a href="#"><span class="glyphicon glyphicon-phone"></span> My contacts</a></li>
          <li><a href="#"><span class="glyphicon glyphicon-phone-alt"></span> All contacts</a></li>
          <li><a href="<?php echo base_url('index.php/Signin/signout'); ?>" title="Signout"><span class="glyphicon glyphicon-log-out"></span> Signout</a></li>
        </ul>
      </li>
      <?php else: ?>
      <li><a href="#"><span class="glyphicon glyphicon-log-in"></span> Signin</a></li>
      <li><a href="#"><span class="glyphicon glyphicon-user"></span> Register</a></li>
      <?php endif;?>
    </ul>
 </div>