Q:

Entity without database

I'm using Symfony 2.7.x
My goals :
1/ A form where the user chooses the figures
2/ Form submitting
3/ Compute something with the help of the submitted data
4/ Display the value
Then I want to create a form, an entity but I don't need any database. 
<? php

namespace RD\FicheBundle\Controller;

use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
use RD\FicheBundle\Entity\Donnees;
use RD\FicheBundle\Form\DonneesType;

class ThController extends Controller
{

// ... code

    public function calculsAction(Request $request)
    {

        $donnees = new Donnees();

        $form = $this->get('form.factory')->create(new DonneesType(), $donnees); 

        $form->handleRequest($request);

        if ($form->isValid())
            {

            // What should I use right here to get my data from the form? 
            // ??????????????????????? 

            // My calculation

            $monney= $log_num*$surf_num*$ann_num*$chauff_num*$del_num;

            $CO2 = 200*$log_num*$surf_num*$ann_num*$chauff_num*$del_num;

            // Getting back the data to the template to display them

            return $this->render('RDFicheBundle:Th:calculs.html.twig', array(
            'form' => $form->createView(),
            'monney' => $monney,
            'CO2' => $CO2
            ));

            }

        // ... code

    }

}

? >

How to get the data coming from the form without doing anything with a database?  Should I use an entity? 

A:

Form arent't expecting any storage/database layer if you dont't tell them to. ( like with field types: entity, and options on other ones.) 
In your case:
Getting the data from submitted (or unsubmitted) form is simple as
 $form->getData()

If you do this after your $form->handleRequest($request); line, you will get submitted data. 
You can also check if you form was submitted with $form->isSubmitted(), which return an boolean true/false. 
If you want your form to populate the submitted data to associated entity (object), you just need set data_class in your form type like this
/**
 * @inheritdoc
 */
public function configureOptions(OptionsResolver $resolver)
{
    $resolver->setDefaults([
        'data_class' => 'Acme\AppBundle\Entity\Example'
    ]);
}

data_class option can be set also for separate, fields(types) of your form, if you got some more complex scenario. 
These docs should help you here:
http://symfony.com/doc/current/book/forms.html#creating-form-classes
Also here you can see that forms are NOT persisted to db automaticly:
http://symfony.com/doc/current/book/forms.html#forms-and-doctrine

