how to create login page with validation in codeigniter

  Cop and paste the code into the login page 

  <div id="login-container">
      <div id="login">
        <?php 
           if(validation_errors() || !empty($error))
             {
         ?>

     <div class="errorMessage login">

        <?php 
            echo validation_errors();
            echo displayMessage($error);
        ?>

     </div>

        <?php
          echo form_open(site_url('user'));
         ?>
     <div class="form-group">
            <?php
                    $usernameField = array(
                               'name'            => 'username',
                               'id'              => 'username',
                               'maxlength'       => '50',
                               'class'           => 'form-control',
                               'placeholder'     => 'username',
                               'autocomplete'    => 'off',
                               'value'           => set_value('username'));
                  echo form_input($usernameField);
            ?>
     </div>
     <div class="form-group">
            <?php
                  $passwordField = array(
                               'name'            => 'password',
                               'id'              => 'password',
                               'maxlength'       => '50',
                               'class'           => 'form-control',
                               'autocomplete'    => 'off',        
                               'placeholder'     => "Password");
                echo form_password($passwordField);
           ?>
     </div>
     <div class="form-group">

      <?php

   echo form_submit('login','Sign in','id="login-btn" class="btn btn-primary btn-block"');    ?>
   </div>
        <?php 

           echo form_close();

        ?>  
        <?php 

           $this->session->sess_destroy(); 

        ?>     
      </div>
    </div>