How to use worksheet names as variables in Excel VBA - vba

Question

I am trying to write a macro that will prompt the user to open 2 workbooks and then loop through the worksheets in the 2 books comparing their contents and highlighting any differences in yellow. Each piece seems to be working on its own, but I cannot figure out how to set the workbook names as global variables to be used between the functions in my sub. Any help would be appreciated! :)
Public strFile1 As String
Public strFile2 As String
Public wbSource1 As Workbook
Public wbSource2 As Workbook
Public I As Integer
Sub DifferenceCheckBetweenBooks()
Call openIt
Call WorksheetLoop
End Sub
Function openIt()
strFile1 = Application.GetOpenFilename
Workbooks.Open strFile1
Set wbSource1 = Workbooks.Open(strFile1)
strFile2 = Application.GetOpenFilename
Workbooks.Open strFile2
Set wbSource2 = Workbooks.Open(strFile2)
End Function
Function WorksheetLoop()
Dim WS_Count As Integer
WS_Count = Workbooks(wbSource1).Worksheets.Count
' Begin the loop.
For I = 1 To WS_Count
Call compareBooks
Next I
End Function
Function compareBooks()
Dim mycell As Range
'For each cell in worksheet that is not the same as compared worksheet, color it yellow
For Each mycell In Workbooks(wbSource1).Worksheets(I).UsedRange
If Not mycell.Value = Workbooks(wbSource2).Worksheets(I).Cells(mycell.Row, mycell.Column).Value Then
mycell.Interior.Color = vbYellow
Workbooks(wbSource2).Worksheets(I).Cells(mycell.Row, mycell.Column).Interior.Color = vbYellow
End If
Next
Workbooks(wbSource2).Worksheets(I).Select
End Function
I am getting the classic "subscript out of range error" which points to my wbSource1 variable as empty.

Answer 1

Don't do this
Workbooks.Open strFile1
Set wbSource1 = Workbooks.Open(strFile1)
you only need
Set wbSource1 = Workbooks.Open(strFile1)
And as SJR points out:
WS_Count = wbSource1.Worksheets.Count 'plus all other instances of this
You should really refactor your code to remove the globals and use parameters in your methods instead - that's a much safer approach.
Refactored to remove globals:
Sub DifferenceCheckBetweenBooks()
Dim wb1 As Workbook, wb2 As Workbook
Set wb1 = OpenIt("Choose first file")
If wb1 Is Nothing Then Exit Sub
Set wb2 = OpenIt("Choose second file")
If wb2 Is Nothing Then Exit Sub
CompareWorkbooks wb1, wb2
End Sub
Sub CompareWorkbooks(wb1 As Workbook, wb2 As Workbook)
Dim i As Long, sht1 As Worksheet, sht2 As Worksheet, c As Range, c2 As Range
For i = 1 To wb1.Worksheets.Count
Set sht1 = wb1.Worksheets(i)
Set sht2 = wb2.Worksheets(i)
For Each c In sht1.UsedRange.Cells
Set c2 = sht2.Range(c.Address)
If c.Value <> c2.Value Then
c.Interior.Color = vbYellow
c2.Interior.Color = vbYellow
End If
Next c
Next i
End Sub
Function OpenIt(msg As String) As Workbook
Dim strFile
strFile = Application.GetOpenFilename(Title:=msg)
If Len(strFile) > 0 Then Set OpenIt = Workbooks.Open(strFile)
End Function