cell auto update from a vlookup result

[alphio]

Hello, I am organizing my own stock control using Excel 2010 and I am stuck with a little problem.

I have a workbook full of products that need to be dispatched on a daily base. I managed to create a vlookup routine linked with an optical scanner
that via bar code returns me the infos of each product including the actual quantity (which I have been updating manually). Is there any way to automatically update the stock to -1 for every scan done? This should happen in the background. The user must have on the screen a simple page with an input field (for the bar code) and a confirmation button. I understand that this could be obtained in VB and unfortunately, although I am quite advanced in Excel, I never used any VB. Any one with an idea would be extremely helpful.

[liybpg]

Maybe I didn't quite understand the description, but could you do: count(all products) - count(info returned on the product dispatched) = stock?

It would be best if you could include a spreadsheet example of what oyu are trying to do (deleting all the sensitive info of course)

[alphio]

Hello and thanks for the reply however I thing I need to explain my problem a little better.
I am trying to use the spreadsheet as a dynamic database. I have 1 page full of products infos called "products":

EAN code (barcode)
Description
Cost
selling price
Quantity

On another page called "shipping" I have an input field where I enter the barcode and via vlookup reads the infos on the "products" page and return it on to the "shipping page". So far is all good. Now.....how do I make excel to change to existing quantity to x-1? Of course it looks to me like a dynamic operation cos it need to point to same record (row) where it took the infos from via lookup.
I have attached a screenshot of an example.

Thank you for your help

Alphio