Add form fields

[Ogre]

I am a total noob to php and html forms so please be gentle with me
Firstly, so far so good, formmail does what I want it to and the emails show the content I need. Now...
I am trying to create an order form where users select from 45 items...either 10 or 20 per order. (e.g. 3 of one...2 of another and 5 of another item to total 10 items)
is there a simple way to add the number of items and show the total in a box
here's my form to date
(I haven't set up the templates yet, that will happen later)
Any suggestions appreciated
Thanks

[david_de]

I think derived fields is what you want. You can combine several fields to make a new field.

[Ogre]

Thanks for the prompt reply :-)
can you elaborate on that or point me to an example of that in use so I can get the idea?
Like I said, total noob
thanks again

[themanwhowas]

as the link suggests

<input type="hidden" name="derive_fields"
value="email = EmailAddress, realname = FirstName + LastName" />

or if you had 5 forms named item1, item2, item3, itm4 and item5 and you wanted them processed as one field

<input type="hidden" name="derive_fields"
value="items = item1 + item2 + item3 + item4 + item5" />