I am wondering if there is a macro that will add column "A" and column
"B" then post final output to column "C"

I have seen some formulas that work but they are very specific like:
=SUM(A8,B8)C8
I need to be able to calculate "All of A + B columns" not just A8
Also some times colums "B" will be empty

Thanks in advance
Jenny the Excell Newbee