macro: if radio button on then copy formula down a range - vba

Question

My prob is this:
I want to be able to use a macro to copy & calculate formula down a range of cells if radio button is on.
But I don't know how to set the variable inside the formula. The macro below should copy the formula to ranges shown (I12:I252, K12:K252, M12:M252).
The formula itself includes a subtraction of two cells in the range of C12:C252 & B12:B252. I cannot seem to reference those cells. I thinks that's the problem...
Anyway, it doesn't work. Any help would be greatly appreciated.
Thanks!
Dim shp1 As Shape
Dim shp2 As Shape
Dim i As Long
On Error Resume Next
Set shp1 = Worksheets("Worksheet").Shapes("Button 1")
Set shp2 = Worksheets("Worksheet").Shapes("Button 2")
If shp1.ControlFormat.Value = xlOn Then
MsgBox "Auto Calculating"
For i = 12 To 252
Range("I" & i).Formula = "=IFERROR(((C & i)-(B & i))*I6/(E7-E6);"")"
Range("K" & i).Formula = "=IFERROR(((C & i)-(B & i))*J6/(E7-E6);"")"
Range("M" & i).Formula = "=IFERROR(((C & i)-(B & i))*K6/(E7-E6);"")"
Next i
Else
If shp2.ControlFormat.Value = xlOn Then
MsgBox "Manually insert calculation"
End If
End If

Answer 1

Few improvements:
Replace the ; in your formulas with ,. ; is your local
setting, but .Formula uses the English setting!
If you want to refer to each column, you need place the i outside the quoatation marks, i.e. instead of =IFERROR(((C & i)... write =IFERROR(((C" & i & ")...
No need to loop each cell and set the formula. If you use $ in your formula properly, you can replace all with one formula: =IFERROR(($C12-$B12)*I$6/($E$7-$E$6),"")
Better use .FormulaR1C1 - this way, your formula will also work, when you would applied it to some other range. To easily convert a formula, type it normally into a cell and the run ? Selection.FormulaR1C1in the VBA Immediate Window. The above formula translates to =IFERROR((RC3-RC2)*R6C/(R7C5-R6C5),"")
Don't hard code cell references (in your case I12:K252). Better assign this range to a named range and use this as a reference. This way, your code will also work if you later add/remove rows or columns.
Don't use On Error Resume Next! This is a invitation to oversee an error that should be fixed
Optional: Alternatively to accessing the controls directly in VBA, you can also assign each one to a cell, name this cell as in step 4 and refer to in by this name. Makes your code more flexible/less complex!
So all in all, I end up with:
Public Sub YourSub()
If Range("SwitchOne") Then
Range("YourRange").FormulaR1C1 = _
"=IFERROR((RC3-RC2)*R6C/(R7C5-R6C5),"""")"
Else
If Range("SwitchTwo") Then
MsgBox "Manually insert calculation"
End If
End If
End Sub