Macro to Validate data in Column B based on Column A

Hello!
I'm trying to create a macro that will check to see if the data the user is inputting is valid for the row.
For example:

User will input into Column A2 - "4444" and then SHOULD enter into Column B2 - "3" or "4".
However* there are times where A2 might have a different value in which B2 will have anything but 3 or 4 entered.

I'm extremely new to VBA/Excel programming and i'm unsure how to do this so that it checks each row as its being entered.

If i am being too vague, i apologize and will try to clear anything up.

Thank you in advance.

Lawliet,

Why not use data validation? You could setup a dependent drop-down list, no VBA required
Intro to data validation: http://www.contextures.com/xlDataVal01.html
Making dependent lists: http://www.contextures.com/xlDataVal02.html

Originally Posted by tigeravatar

Lawliet,

Why not use data validation? You could setup a dependent drop-down list, no VBA required
Intro to data validation: http://www.contextures.com/xlDataVal01.html
Making dependent lists: http://www.contextures.com/xlDataVal02.html

The data/worksheet will be put through a different macro/uploaded into various programs and i'm unsure how they would handle that without further manipulation. Also this would need to be able to accept a much wider range of numbers if certain other inputs are used for A2. I apologize for not stating that earlier. Thank you for the suggestion though.

I'm only so so with VBA but is this what you are looking for? (see attachment)
code is in worksheet as follows

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I used 3 rules
if a = 4444 b has to be 3 or 4
if a is empty then can't fill in b
if a <> 4444 then b cannot be 3 or 4