i can't disply form

[dev_mohamed]

dear all,
i am new in zend i have this code and try to use zend form and nothing in my browser i can't see any thing please help

my directory like this
/a.php
/Zend

it just print End of file

<?php
require_once 'Zend/Form.php';
require_once 'Zend/Config.php';
require_once 'Zend/Validate.php';
require_once 'Zend/Validate/Alnum.php';
require_once 'Zend/Filter.php';
require_once 'Zend/Loader.php';
require_once 'Zend/View.php';


$form = new Zend_Form;
$form->setAction('./')
->setMethod('post');
$form->setAttrib('id', 'login');

// Passing a form element type to the form object:
$form->addElement('text', 'username');
$username = new Zend_Form_Element_Text('username');

// Passing a validator name:
// Pass a pattern
// Make this element required
$username->addValidator('alnum')
->addValidator('regex', false, array('/^[a-z]/'))
->setRequired(true)
->addFilter('StringToLower');

// Assuming a view object has been previously set via setView():
echo $form;


if (!$form->isValid($_POST)) {
echo $form ;

// or assign to the view object and render a view...
echo $this->view->form = $form;
return $this->render('form');
}

echo "<br>End of file";
?>