Table cell equation creation

How do I create the following equation?

three column table, the column C equation would be sum(A(n)- B(n)) where 
n is the  cell no matter what row number it is, it will subtract the 
value of cell Column B from cell column A and put value in cell column 
C. I would like this equation to be in the header of column C

Jerry:
> three column table, the column C equation would be sum(A(n)- B(n)) where 
> n is the  cell no matter what row number it is, it will subtract the 
> value of cell Column B from cell column A and put value in cell column 
> C.

Usually one would put into perhaps C3: +A3-B3 and [Copy_Formula] down the 
Column. But I cannot reconcile this with your comment:

> I would like this equation to be in the header of column C
-- 
Good wishes!
Roy Lewis
C_Tech volunteer
(UK)