Most efficent way to re-use static vba code on any row - vba

Question

I am attempting to allow a user to enter a value as a either a percentage, or as a number of hours - with the unused option being auto-populated with a macro using what has been input.
Using the below example if a user were to key in 25 hours, the macro would then add a formula to B2 (shown in B3 for reference) to calculate 25% (of the total shown in C2), this would also work if the user added the percentage to cell B2, it would then populate A2 with the number of hours (again using the total shown in C2).
I have got the macro working to achieve this:
Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
Dim Cell As Range
For Each Cell In Target
If Cell.Address = "$A$2" Then
Application.EnableEvents = False
Range("B2").Formula = "=(A2/C2)*100"
Application.EnableEvents = True
End If
Next Cell
For Each Cell In Target
If Cell.Address = "$B$2" Then
Application.EnableEvents = False
Range("A2").Formula = "=(B2*C2)/100"
Application.EnableEvents = True
End If
Next Cell
End Sub
What I am now trying to establish is there a more efficient way of
re-using this on different rows?
The columns would remain the same but ideally it would work on rows 2 through to 100. At the movement the only option I can think of is to copy the macro multiple times and reference the cells used individuall.
Any pointers or suggestions very much appreciated.

Answer 1

To do all the rows Between 2 and 100 then use this:
Use Intersect to detemine if the cell that changed in in a specific range.
Use R1C1 notation on the formula to ensure that the same row is being evaluated.
The code:
Private Sub Worksheet_Change(ByVal Target As Range)
If Not Intersect(Target, Range("A2:A100")) Is Nothing Then
Application.EnableEvents = False
Target.Offset(, 1).FormulaR1C1 = "=(RC[-1]/RC[1])*100"
Application.EnableEvents = True
End If
If Not Intersect(Target, Range("B2:B100")) Is Nothing Then
Application.EnableEvents = False
Target.Offset(, -1).FormulaR1C1 = "=(RC[1]*RC[2])/100"
Application.EnableEvents = True
End If
End Sub

Answer 2

Just change your tests to look at the column property instead and use relative references - like so:
Private Sub Worksheet_Change(ByVal Target As Range)
Dim Cell As Range
For Each Cell In Target
If Cell.Column = 1 And (Cell.Row >= 2 And Cell.Row <= 100) Then
Application.EnableEvents = False
Cell.Offset(0, 1).FormulaR1C1 = "=(RC[-1]/RC[1])*100"
Application.EnableEvents = True
End If
Next Cell
For Each Cell In Target
If Cell.Column = 2 (Cell.Row >= 2 And Cell.Row <= 100) Then
Application.EnableEvents = False
Cell.Offset(0, -1).FormulaR1C1 = "=(RC[1]*RC[2])/100"
Application.EnableEvents = True
End If
Next Cell
End Sub