Here is a quick tip, lets say you have a Excel spreadsheet, and you quickly need to change a series of values to negative values. You can use the below macro, which demonstrates how to traverse through every cell in a selection and set the value to a negative value. This is useful for accounting formating.
Dim c As Range
'For each cell in your selection
For Each c In Selection
'If the value is not blank, set to a negative version of
If (c.Value <> "") Then
c.Value = c.Value * -1