function kostenrechner_permission() {
  return array(
    'view kostenrechner block' => array(
      'title' => t('View Calculate block'),
      'description' => t('Calculate cost of german divorce')
    ),
  );
}


function kostenrechner_menu() {
  $items = array();

  $items['examples/kostenrechner'] = array(
    'title' => 'Kostenrechner',
    'description' => 'A form to mess around with.',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('kostenrechner_form'),
    'access callback' => TRUE,
    'type' => MENU_NORMAL_ITEM,
  );

  return $items;
}

function kostenrechner_form($form, &$form_state) {
  $form['einkommen'] = array(
    '#type' => 'textfield', //you can find a list of available types in the form api
    '#title' => 'Ihr Einkommen',
    '#size' => 10,
    '#maxlength' => 10,
    '#required' => TRUE, //make this field required
    '#default_value' => isset($form_state['storage']['einkommen']) ? $form_state['storage']['einkommen'] : '',
  );
  $form['einkommen_partner'] = array(
    '#type' => 'textfield', //you can find a list of available types in the form api
    '#title' => 'Das Einkommen Ihres Partners',
    '#size' => 10,
    '#maxlength' => 10,
    '#required' => TRUE, //make this field required
    '#default_value' => isset($form_state['storage']['einkommen_partner']) ? $form_state['storage']['einkommen_partner'] : '',
  );
  $form['kind'] = array(
    '#type' => 'textfield', //you can find a list of available types in the form api
    '#title' => 'Wie viele Kinder haben Sie?',
    '#size' => 10,
    '#maxlength' => 10,
    '#required' => TRUE, //make this field required
    '#default_value' => isset($form_state['storage']['kind']) ? $form_state['storage']['kind'] : '',
  );

  $form['submit_button'] = array(
    '#type' => 'submit',
    '#value' => t('Kosten berechnen'),
  );

return $form;
}

function kostenrechner_form_validate($form, &$form_state) {

     if (
     !($form_state['values']['einkommen'] > 0) or !is_numeric($form_state['values']['einkommen'])

     ){
    form_set_error('price', t('Bitte geben Sie Ihr Einkommen an'));
  }
    if (
    !($form_state['values']['einkommen_partner'] >= 0) or !is_numeric($form_state['values']['einkommen_partner'])
    ){
    form_set_error('price', t('Bitte geben Sie Ihr Einkommen Ihres Partners an'));
  }

}

function kostenrechner_form_submit($form, &$form_state) {

/*** Hier die Berechnung ***/

if(isset($result))
    {

    print $result;
    }
    else
    {
    print 'result is clear';
    }
$form_state['rebuild'] = TRUE;
}