How to set global variables in VBA - excel

Question

I would like to define a global variable in VBA in one module and use this in other VBA modules.
I am trying to follow: How do I declare a global variable in VBA?
I have created a new module called "GlobalVariables", and first declared the Public variables and then set their value within a function (trying to do this in open code causes an error). My code is below.
But the Global variable StartYear does not seem to be available into other VBA modules. What am I doing wrong?
Option Explicit
Public StartYear As Integer
Public BaseYear As Integer
Function DeclareGlobalVariables()
StartYear = ActiveWorkbook.Worksheets("RunModel").Range("StartYear").Value
BaseYear = ActiveWorkbook.Worksheets("RunModel").Range("BaseYear").Value
End Function

Answer 1

Make sure you put your golobal variable in a module and not in worksheet scope, to make it accessible in other modules.
Your Function should be a Sub because it does not return anything.
Your code will error if your cells eg. contain text (strings). Never trust a user's input. Always validate!
So I suggest the following
Module 1
Option Explicit
Public StartYear As Long
Public BaseYear As Long
Public Function InitializeGlobalVariables() As Boolean
InitializeGlobalVariables = True
With ActiveWorkbook.Worksheets("RunModel").Range("StartYear")
If IsYear(.Value) Then
StartYear = CLng(.Value)
Else
InitializeGlobalVariables = False
MsgBox "StartYear needs to be a number"
End If
End With
With ActiveWorkbook.Worksheets("RunModel").Range("BaseYear")
If IsYear(.Value) Then
BaseYear = CLng(.Value)
Else
InitializeGlobalVariables = False
MsgBox "BaseYear needs to be a number"
End If
End With
End Function
'validate if the input value is a valid year
Private Function IsYear(ByVal InputValue As Variant) As Boolean
If IsNumeric(InputValue) Then
If CLng(InputValue) = InputValue And _
InputValue > 0 And InputValue < 9999 Then 'integer not decimal AND 4 digit year
IsYear = True
End If
End If
End Function
And you can access the variables in any other module like:
Module 2
Option Explicit
Public Sub TestOutput()
'before using the variables test if they are initialized (not 0)
If StartYear = 0 Or BaseYear = 0 Then
'they are not initalized so initalize them (and at the same time check if it was successful)
If InitializeGlobalVariables = False Then
'the function returns FALSE if the initialization process failed so we need to cancel this procedure or we use not initilized variables!
MsgBox "Variables were not intitialized. Trying to initialize them failed too. I cannot proceed."
Exit Sub
End If
End If
Debug.Print StartYear
Debug.Print BaseYear
End Sub