Referencing a string value in excel VBA with the indexed cells property - excel

Question

VBA Newbie here with a basic question I've been struggling to find the answer on:
I'm trying to run a loop in VBA that looks up a string (or word) and if that word is found, a specified letter has to appear in a cell in the column beside it. This works fine when I use a specific cell reference (eg Cells(72, 10)), but as soon as I try to loop it using an index (eg Cells(i, 10), it gives an error 13 - type mismatch.
The 'strings' I'm looking up are outputs (either "Peak" or "Trough") from another macro I wrote as a basic calculation function in excel. Is the error as a result of trying to reference a different data type than the "Cells" function can recognise? Or is there just a better way to run my loop? Following are the macro and my loop.
Function FTrough(tmin2, tmin1, t, tplus1, tplus2)
If t < tmin2 And t < tmin1 And t < tplus1 And t < tplus2 Then
FTrough = "Trough"
Else
FTrough = ""
End If
End Function
And the loop":
Sub Lookup()
Dim i As Integer
Dim j As Integer
Dim c As Integer
c = ActiveWorkbook.Worksheets.Count
For i = 1 To c
For j = 2 To 141
If Worksheets(i).Cells(j, 10) = "Trough" Then
Worksheets(i).Cells(j, 12) = "T"
End If
If Worksheets("Austria").Cells(j, 11) = "Peak" Then
Worksheets("Austria").Cells(j, 12) = "P"
End If
Next j
Next i
End Sub
Any help appreciated

Answer 1

I cannot comment because my reput is lower than 50, so here is my answer.
Basically your code works perfectly. I tested it with Excel 2013/VB6 as follows:
Sub Lookup()
Dim i As Integer
Dim j As Integer
Dim c As Integer
c = ActiveWorkbook.Worksheets.Count
For i = 1 To c
For j = 2 To 141
If Worksheets(i).Cells(j, 1) = "Trough" Then
Worksheets(i).Cells(j, 2) = "T"
End If
If Worksheets("Austria").Cells(j, 1) = "Peak" Then
Worksheets("Austria").Cells(j, 2) = "P"
End If
Next j
Next i
End Sub
The function to write the values in Excel:
Public Function X(tmin2, tmin1, t, tplus1, tplus2)
If t < tmin2 And t < tmin1 And t < tplus1 And t < tplus2 Then
X = "Trough"
Else
X = ""
End If
End Function
The values in excel were created by custom as well as e.g. =X(100;100;1;100;100).