You cannot do that with Conditional Format.
Changing a format does not change the underlying value of the cell.
You could use a helper column and enter a formula.........
=IF(B1="c",A1*-1,"not equal c") copy down column C
This won't change the values in column A to negative but will give you a
negative in column C
OR you could use event code to do it in place assuming you have the letters in
column B and are entering numbers in Column A
Private Sub Worksheet_Change(ByVal Target As Excel.Range)
On Error GoTo enditall
Application.EnableEvents = False
If Target.Cells.Column = 1 Then
n = Target.Row
If Target.Offset(0, 1).Value = "c" Then
With Target
.Value = .Value * -1
End With
End If
End If
enditall:
Application.EnableEvents = True
End Sub
Gord Dibben MS Excel MVP