Form Autocomplete example

/**
 * Impelements hook_permission()
 */
function example_permission() {
  return array(
    'example' => array(
            'title' => t('example'), 
            'description' => t('example text.'),
    ),
  );
} 

/**
 * Implements hook_menu().
 *
 * */
 function example_menu(){
    $items['example/autocomplete'] = array(
      'title' => '',
      'page callback' => 'drupal_get_form',
      'page arguments' => array('example_autocomplete'),
      'access arguments' => array('example'),
      'type' => MENU_CALLBACK,
    );
    $items['pincode/autocomplete'] = array(
            'page callback' => 'pincode_autocomplete',
            'access arguments' => array('example'),
            'type' => MENU_CALLBACK
    );
  return $items;
 }
 /**
 * Implements auto complete call back.
 *
 * */
 function pincode_autocomplete($string){
	$matches = array();
	$query = db_select("web_pincode","wcm");
        $query->fields('wcm',array('pin_code'));
        $query->condition('wcm.pin_code', db_like($string) . '%', 'LIKE');
        $query->range(0,15);
        $res = $query->execute();
	while ($res1 = $res->fetchAssoc()) {
		$matches[$res1['pin_code']] = check_plain($res1['pin_code']);
	}
 drupal_json_output($matches);
}
 /**
 * Implements auto complete form().
 *
 * */
 function example_autocomplete($form, &$form_state){
      $form = array();
      $form['pincode'] = array (
		'#type'		=>	'textfield',
		'#title'	=>	t('Pincode'),
		'#required' =>	 TRUE,
		'#autocomplete_path' => 'pincode/autocomplete',                    // attribute for autocomplete
      '#description' => t('Enter six digit pincode (e.g. 710710).'),
     ); 
      $form['user_submit'] = array(
        '#type' => 'submit',
        '#value' => t('Create user'),
        '#name' => 'create-user',
        '#prefix' => '<div id = "create-group">',
        '#suffix' => '</div>',
      );
    return $form;
  }