excel vba compare 2 columns and list non matching results - excel

Question

I try to compare two columns and get the non-matching results listed somewhere else.
So far I've come up with the following:
Sub match_columns()
Dim i, Lastrow1, Lastrow3 As Integer
Dim found As Range
With Worksheets("sht1")
Lastrow1 = .Range("A" & Rows.Count).End(xlUp).Row
For i = 1 To Lastrow1
answer1 = .Range("A" & i).Value
Set found = Sheets("sht2").Columns("A:A").Find(what:=answer1)
If found Is Nothing Then
Set rngNM = .Range("A" & i.Row)
Else
Set rngNM = Union(rngNM, .Range("A" & i.Row))
End If
Next i
End With
If Not rngNM Is Nothing Then rngNM.Copy Worksheets("sht3").[A2]
Worksheets("sht3").[A1] = "title"
Lastrow3 = Sheets("sht3").Range("A" & Rows.Count).End(xlUp).Row
Sheets("sht3").Range("A2:A" & Lastrow3).Copy
End Sub
I currently get an "Runtime error 424; Object required" for the following:
Set rngNM = .Range("A" & i.Row)
Where is my code wrong?

Answer 1

Try this code
Sub Compare_Two_Columns()
Dim ws As Worksheet, sh As Worksheet, out As Worksheet, c As Range, i As Long, m As Long, k As Long
Application.ScreenUpdating = False
Set ws = ThisWorkbook.Worksheets("Sheet1")
Set sh = ThisWorkbook.Worksheets("Sheet2")
Set out = ThisWorkbook.Worksheets("Sheet3")
m = ws.Range("A" & Rows.Count).End(xlUp).Row
ReDim a(1 To m)
For i = 1 To m
Set c = sh.Range("A:A").Find(What:=ws.Cells(i, 1).Value, LookAt:=xlWhole)
If c Is Nothing Then k = k + 1: a(k) = ws.Cells(i, 1).Value
Next I
If k > 0 Then
With out
.Range("A1").Value = "Title"
.Range("A2").Resize(k).Value = Application.Transpose(a)
End With
End If
Application.ScreenUpdating = True
MsgBox "Done...", 64
End Sub