function company_form()
    {
         $form['company_username'] =  array(
          '#type' => 'textfield',
          '#title' => 'company-username',
          '#default_value' => '',
              '#required'=>'true'
      );
          $form['company_email'] =  array(
          '#type' => 'textfield',
          '#title' => 'company-email',
              '#required'=>'true',
          '#default_value' => '',
          '#element_validate' => array('generate_special_form_validate'),
      );
           $form['company_password'] =  array(
          '#type' => 'textfield',
          '#title' => 'company-password',
               '#required'=>'true',
          '#default_value' => ''
      );

      $form['submit'] =  array(
          '#type' => 'submit',
          '#title' => '',
          '#value' => 'Submit',
          '#default_value' => ''
      );
      return $form;
    }
    function company_form__validate(&$form_state,$form) {

         if (!valid_email_address($form['input']['email'])) {
         form_set_error($form['input']['email'],'Please enter a valid email address.');
       }
    }
    function company_form_submit($form, &$form_state)
    {


     global $user;
        $company_username = $form_state['input']['company_username'];
        $company_email = $form_state['input']['company_email'];
        $company_password = $form_state['input']['company_password'];
         $fields = array(
              'name' => $company_username,
              'pass' =>$company_password,
              'mail' => $company_email,
              'init' => $company_email,
              'status' => 1,
              'access' => REQUEST_TIME,
              'roles' => array(
               4 => 'company',
                ),

        );
        $account=user_save('', $fields);


    if($account->uid)
    {
     drupal_set_message('User Created SuccessFully');
    }

}

'roles' => array(
               4 => 'company',
                ),

/**
 * Implements hook_form_BASE_ID_alter()
 */
function CUSTOM_MODULE_form_user_register_form_alter(&$form, &$form_state, $form_id) {
  // Get the system roles.
  $roles = array_map('check_plain', user_roles(TRUE));

  $form['roles'] = array(
    '#type' => 'select',
    '#title' => t('Roles'),
    '#default_value' => array(),
    '#options' => $roles,
  );
}

/**
 * Implements hook_user_insert()
 */
function CUSTOM_MODULE_user_insert(&$edit, $account, $category) {
  // Save the role if it's set.
  if (isset($edit['roles'])) {
    // Push the roles to $account object so that user_save can get the role property.
    $account->roles[] = $edit['roles'];
  }
}