My VBA skills are a little rusty, but this is the general idea of what I'd do.
The easiest way to do this would be to iterate through a loop for every column:
public sub CellProcessing()
on error goto errHandler
dim MAX_ROW as Integer 'how many rows in the spreadsheet
dim i as Integer
dim cols as String
for i = 1 to MAX_ROW
'perform checks on the cell here
'access the cell with Range("A" & i) to get cell A1 where i = 1
next i
exitHandler:
exit sub
errHandler:
msgbox "Error " & err.Number & ": " & err.Description
resume exitHandler
end sub
it seems that the color syntax highlighting doesn't like vba, but hopefully this will help somewhat (at least give you a starting point to work from).