Good morning

I'm trying to obtain some help on what I'm hoping is a rather easy issue

What I'm trying to accomplish is to have Excel read the value in one column and depending what that value is only allow input in one of the next 2 columns (there will then be more columns after that that need full access to, but the 3 columns are what I'm concentrating on)

The value in "Column A" could be any number of different numbers. As a small example, I'll make a basic diagram of only these 3 columns

Code Credit Debi
06 xx.x
21 xx.x
34 xx.x
95 xx.x

The codes would obviously all be something I imagine I have to put into the scripting to make it know where to let the user make the corresponding input in either column 2 or 3

Any help to get started on a solution would be very much appreciated. As it is we have a LOT of people who still can't grasp that a certain code should be for Credit yet they put it in the Debit column (and vice versa). Worst of all they use the same code multiple times in their work and have the $$ amount in different columns in the same file!! ugh.