Dropdown not getting validated

Code:

&lt;?php echo form_label('Recipient', 'recipient'); ?&gt;

&lt;?php 

$options = array();

$options[0] = '<option></option>';

foreach($users AS $user)

{

    $options[$user->user_id] = $user->first_name.' '.$user->last_name;

}

?&gt;

&lt;?php echo form_dropdown('recipient', $options, -1, 'class=required'); ?&gt;

Code:

&lt;?php

$options = array(

                  'small'  => 'Small Shirt',

                  'med'    => 'Medium Shirt',

                  'large'   => 'Large Shirt',

                  'xlarge' => 'Extra Large Shirt',

                );



$shirts_on_sale = array('small', 'large');



echo form_dropdown('shirts', $options, 'large');

?&gt;

Code:

&lt;?php echo form_label('Recipient', 'recipient'); ?&gt;

                                    &lt;?php 

                                    $options = array();

                                    foreach($users AS $user)

                                    {

                                        $options[$user->user_id] = $user->first_name.' '.$user->last_name;

                                    }

                                    ?&gt;

         &lt;?php echo form_multiselect('recipient', $options, set_value('recipient', 0), 'class=required'); ?&gt;

Code:

// Function used for login form validation

    function pm_submit()

    {

        $outputArray = array('error' => 'yes', 'message' => 'unproccessed');

        $outputMsg = '';

        

        // Sets validation rules for the login form

        $this->form_validation->set_rules('recipient', 'Recipient', 'required|integer');

  $this->form_validation->set_rules('subject', 'Subject', 'trim|required|xss_clean');

  $this->form_validation->set_rules('message', 'Message', 'trim|required|xss_clean');

        $this->form_validation->set_rules('sender', 'Sender', 'required|integer');

        

        // Checks to see if login form was submitted properly

        if (!$this->form_validation->run()) 

        {

         

            $outputArray['message'] = 'There was a problem submitting the form! Please refresh the window and try again!'; 

            

        }

        else

        {

            // Retrieves users from database with posted user ids

            $recipient = $this->users->get_user_by_user_id($this->input->post('recipient'));

            $sender = $this->users->get_user_by_user_id($this->input->post('sender'));

            

            // Verifies users were returned from database

            if (($recipient == FALSE) || ($sender == FALSE))

            {

                // Users was not found in the database

                $outputArray['message'] = 'Either the recipient or yourself could not be found in the database!';

            }

            else

            {

                if ($this->pmmmodel->allows_pms($this->input->post('recipient')))

                {

                    if ($this->pmmodel->send_pm($this->input->post('recipient'), $this->input->post('subject'), $this->input->post('message'), $this->input->post('sender'))) 

                    {

                        $outputArray = array('success' => 'Yes', 'message' => 'Message was sent successfully!');    

                    }

                    else

                    {

                        $outputArray['message'] = 'Message could not get sent!';

                    }

                }

                else

                {

                    $outputArray['message'] = 'Recipient does not allow to be messaged!';

                }

            }

        }

        echo json_encode($outputArray); 

    }