How to add a field to the registration form programmatically?

Question

Drupal

How to add a field to the registration form programmatically? Well and to keep this value?
I'm looking in the direction of hook_form_alter () but I don't understand how it works yet

Answer 1

function yourmodulename_form_alter(&$form, &$form_state, $form_id) {
    if ($form_id == 'user_register_form') {
        $form['newfield'] = array(
            '#type' => 'textfield',
            '#title' => t('Sample field')
        );
    }
}

But about saving - that's another question. Depends on where to save and in what form. It is possible to do a sheaf with fields what that at the created user. Specify the question.