What is wrong in my macro code? - vba

Question

I tried to write comparison in Excel macro for my work. Somehow, it is working not in the way I wanted the output. What I want is to compare the two columns and show the differences between them. If empty field on one column, the program should skip a line. Here is my code:
Sub run_compare_main()
Application.Calculation = xlCalculationManual
Application.ScreenUpdating = False
Dim last_row As Integer
Dim input_array As Variant
Dim output_aray() As String
Dim a_counter As Integer
Dim b_counter As Integer
last_row = get_last_row("INPUT", "A")
ReDim output_array(1 To (last_row * 2), 1 To 5) '(last_row * 2)
input_array = Range("A7:D7" & (last_row * 2)).Value2
a_counter = 1
b_counter = 1
For i = 1 To (last_row * 2)
If input_array(a_counter, 1) = input_array(b_counter, 3) Then
output_array(i, 1) = input_array(a_counter, 1)
output_array(i, 2) = input_array(a_counter, 2)
output_array(i, 3) = input_array(b_counter, 3)
output_array(i, 4) = input_array(b_counter, 4)
a_counter = a_counter + 1
b_counter = b_counter + 1
ElseIf input_array(a_counter, 1) = input_array(a_counter - 1, 1) Then
output_array(i, 1) = input_array(a_counter, 1)
output_array(i, 2) = input_array(a_counter, 2)
a_counter = a_counter + 1
ElseIf input_array(b_counter, 3) = input_array(b_counter - 1, 3) Then
output_array(i, 3) = input_array(b_counter, 3)
output_array(i, 4) = input_array(b_counter, 4)
b_counter = b_counter + 1
End If
'find smaller value
If input_array(a_counter, 1) < input_array(b_counter, 3) Or input_array(b_counter, 1) = "" Then
output_array(i, 1) = input_array(a_counter, 1)
output_array(i, 2) = input_array(a_counter, 2)
a_counter = a_counter + 1
Else
output_array(i, 3) = input_array(b_counter, 3)
output_array(i, 4) = input_array(b_counter, 2)
b_counter = b_counter + 1
End If
If a_counter = last_row - 5 Or b_counter = last_row - 5 Then
Exit For
End If
Next
Call newtab("OUTPUT")
Range("A7").Resize(last_row, 4).Value = output_array
Sheets("INPUT").Range("A5:D6").Copy
Sheets("OUTPUT").Range("A5").Select
ActiveSheet.Paste
Columns("B:B").ColumnWidth = 80
Columns("D:D").ColumnWidth = 80
Dim LastCol As Long
Dim LastRow As Long
LastCol = ActiveSheet.UsedRange.Columns.Count
LastRow = ActiveSheet.UsedRange.Rows.Count
FilePath = "D:\Try\support.txt"
Open FilePath For Output As #2
CellData = ""
For i = 1 To LastRow
For j = 1 To LastCol
CellData = "The Value at location (" & i & "," & j & ") " & Trim(ActiveCell(i, j).Value)
Write #2, CellData
Next j
Next i
Close #2
MsgBox ("Job Done")
End Sub
Sub newtab(sheetname As String)
Application.DisplayAlerts = False
On Error Resume Next
Sheets(sheetname).Delete
Application.DisplayAlerts = True
Sheets.Add After:=Sheets(Sheets.Count)
Sheets(Sheets.Count).Activate
Sheets(Sheets.Count).Name = sheetname
End Sub
Function get_last_row(ByVal sheetname As String, column As String) As Integer
With Sheets(sheetname)
If Application.WorksheetFunction.CountA(.Cells) <> 0 Then
LastRow = .Cells.Find(What:="*", _
After:=.Range(column & "1"), _
Lookat:=xlPart, _
LookIn:=xlFormulas, _
SearchOrder:=xlByRows, _
SearchDirection:=xlPrevious, _
MatchCase:=False).Row
End If
End With
get_last_row = LastRow
End Function
and here my worksample: