How to loop indices of .formula/.formulaR1C1 - excel

Question

I am stuck with a problem i cannot get my head around currently.
I have a checklist that has to update automatically when adding lines to my excel worksheet so that the checklist is applied to all rows.
I tried to use a "for loop" to modify the formula but excel returns Error 1004, when starting the string with "=".
No error but no functionality as well:
ActiveWorkbook.Sheets("Kalkulation Änderungen").Range("AB9").FormulaLocal = "Wenn(Oder(AB" & firstRow & "=""x"""
Returns error 1004:
ActiveWorkbook.Sheets("Kalkulation Änderungen").Range("AB9").FormulaLocal = "=Wenn(Oder(AB" & firstRow & "=""x"""
My first solution
Loop FormulaR1C1, or Formula and use nothing but english Function names eg. sum() instead of Summe() and follow english syntax , instead of ;.
Problem
When testing the syntax without a loop and actual indices it works like a charm. As soon as I try to loop it, Excel does not recognize R[i]C as cell anymore but just returns plain text.
no issues:
ActiveWorkbook.Sheets("Kalkulation Änderungen").Range("AB9").Formula = "IF(OR( R[1]C = ""x"""
issues:
ActiveWorkbook.Sheets("Kalkulation Änderungen").Range("AB9").Formula = "IF(OR( R[i]C = ""x"""
Splitting it like this did not solve my problem either
..R[" & i & "]C =..
Any tips?
// For i= ... to .. next i
// Excel 2007

Answer 1

Try this:
With ActiveWorkbook.Sheets("Kalkulation Änderungen")
'find last row of column AB
LastRow = .Cells(.Rows.Count, "AB").End(xlUp).Row
'apply the formula from AB9 to its last non-blank row
.Range("AB9:AB" & LastRow).Formula = "IF(OR( R[1]C = ""x"""
End With

Answer 2

#UGP: that is what i thought the code might look like after implementing your tips with intersect etc.
What do you think of it, I guess you might not like the loops too much?
Typical beginner approach to loop everything?
I would have to do this for every column accordingly?
If so it would be wise to create a sub () for every column with an exit condition so that i save computing time?
Unless it is possible to hand over the columnadress to the sub_worksheet_change()?
Private Sub Worksheet_Change(ByVal Target As Range, selected_column)
_
_
_
_
Private Sub Worksheet_Change(ByVal Target As Range)
Dim KeyCells As Range
Dim i As Integer
Dim check As Boolean
frstRow = 1
lastRow = 1
i = 1
'Rowcount
Do Until firstRow <> 1 And lastRow <> 1
If ActiveWorkbook.Sheets("Kalkulation Änderungen").Range("D" & i) = "Länge" Then
firstRow = i + 2
i = i + 1
End If
If ActiveWorkbook.Sheets("Kalkulation Änderungen").Range("G" & i) = "Gesamt-h" Then
lastRow = i - 2
End If
i = i + 1
Loop
' check column AB fo "x" and modify header
Set KeyCells = Range("AB" & firstRow, "AI" & lastRow)
check = False
i = firstRow
If Not Application.Intersect(KeyCells, Range(Target.Address)) _
Is Nothing Then
Do While i <= lastRow And check = False
If ActiveWorkbook.Sheets("Kalkulation Änderungen").Range("AB" & i).Value = "x" Then
check = True
ActiveWorkbook.Sheets("Kalkulation Änderungen").Range("AB9").Value = "x"
ElseIf i = lastRow And check = False Then
ActiveWorkbook.Sheets("Kalkulation Änderungen").Range("AB9").Value = " "
End If
i = i + 1
Loop
End If
End Sub

Answer 3

Here's the code. It has to be in the corresponding worksheet in the VBA-Editor.
It activates when a cell in Range(A10:A20) has been changed.
Private Sub Worksheet_Change(ByVal Target As Range)
Dim KeyCells As Range
Set KeyCells = Range("A10:A20")
If Not Application.Intersect(KeyCells, Range(Target.Address)) _
Is Nothing Then
If Target.Count = 1 Then
If Target.Value = "x" Then
'Your Code
'i.e
MsgBox (Target.Address & "has been changed")
End If
Else
MsgBox ("Please No Copy Pasterino")
End If
End If
End Sub
EDIT:
Private Sub Worksheet_Change(ByVal Target As Range)
Dim KeyCells As Range
Dim i As Integer
Dim fRow As Long, lRow As Long
Dim check As Boolean
Dim sht As Worksheet
Dim Cell As Range
Set sht = Worksheets("Tabelle1")
'Rowcount
fRow = 2
lRow = sht.Cells(sht.Rows.Count, "G").End(xlUp).Row
' check column AB fo "x" and modify header
Set KeyCells = Range("AB" & fRow & ":AI" & lRow)
If Not Application.Intersect(KeyCells, Range(Target.Address)) _
Is Nothing Then
For Each Cell In Range(Cells(fRow, Target.Column), Cells(lRow, Target.Column))
If Cell.Value = "x" Then
sht.Cells(9, Target.Column).Value = "x"
Exit For
Else
sht.Cells(9, Target.Column).Value = ""
End If
Next
End If
End Sub