I want to populate specific column values with a zero if
the value in another specified column is not null.

As an example, I would like to place a 0 in columns C & E
of my spreadsheet if the value in column A is null.

I presume that I would have to start by specifying the
range which I would like this macro to work over. If that
is so, is it possible for the range to set itself by using
any row that has data on it (bar row1) ? This way, the
range can vary depending on how many rows of data are in
the spreadsheet at any given time.

Thanks in advance.