Dynamic Field Adition / Subtraction using FAPI

Question

Goal Provide a user with a drop down menu defaulted to a value of none. Other options are the number 1 through 27. Based on the value select have drupal FAPI generate a fieldset that has anywhere from 1 to 27 required text fields. And should they then change their mind it would re-render accordingly.

What I have So far I am able to get the FAPI to hide the field on initial form render however I can't seem to figure out how I'd take the selected array value and use that to generate out a new field set dynamically.

function single_add_ucm_form($form, &$form_state) {
$form['number_subscribers'] = array(
'#type' => 'select',
'#title' => t('How many subscribers are in the CUCM cluster?'),
'#required' => TRUE,
'#default_value' =>  0,
'#ajax' => array(
  'callback' => 'ajax_select_callback',
  'wrapper' => 'replace_subscribers_div',
  'effect' => 'slide',
 ),
'#options' => array(
  0 => t('none'),
  1 => t('1'),
  2 => t('2'),
  3 => t('3'),
  4 => t('4'),
  5 => t('5'),
  6 => t('6'),
  7 => t('7'),
  8 => t('8'),
  9 => t('9'),
  10 => t('10'),
  11 => t('11'),
  12 => t('12'),
  13 => t('13'),
  14 => t('14'),
  15 => t('15'),
  16 => t('16'),
  17 => t('17'),
  18 => t('18'),
  19 => t('19'),
  20 => t('20'),
  21 => t('21'),
  22 => t('22'),
  23 => t('23'),
  24 => t('24'),
  25 => t('25'),
  27 => t('26'),
  27 => t('27'),
),
);
$form ['subscribers_wrapper_container'] = array(
'#type' => 'container',
'#prefix' => '<div id="replace_subscribers_div">',
'#suffix' => '</div>',
);

if (isset($form_state['values']['number_subscribers'])) {
$form_state >= 1;
$form['subscribers_wrapper_container']['UCM_SUB'] = array(
    '#type' => 'textfield',
    '#size' => 30,
    '#title' => t('Subscriber IP Address'),
    '#required' => TRUE,
  );
}
}


function ajax_select_callback($form, $form_state) {
return $form['subscribers_wrapper_container'];
  }

Answer 1

if (!isset($form_state['values']['number_subscribers'])) {
   $form_state['values']['number_subscribers'] = 0;
}

for($i = 0; $i < $form_state['values']['number_subscribers']; $i++){
$form['subscribers_wrapper_container'][]['UCM_SUB'] = array(
    '#type' => 'textfield',
    '#size' => 30,
    '#title' => t('Subscriber IP Address'),
    '#required' => TRUE,
  );
}

You should add '#tree' => TRUE on your form, it will be easier to extract the form values afterwards