VBA: problems with defining variables in function

Question

I have the following problem:

Option Explicit is used.

the code

Function myFun( myVar as Double) as double
    myVar = myVar + 1
end function

throws an error that myVar is not defined

however, if I add the line Dim myVar as Double it says that the variable is declared twice.

What am I doing wrong?

Thanks

Answer 1

Based on your comment to Vityata's question, let me try a slightly different way of explaining things.

You need to think about the Scope of the variable.

Consider that you have two separate procedures:

Procedure 1

Public Sub TestMe()
    Dim myVar As Double
    myVar = 5
    Debug.Print myFun(myVar)
End Sub

Procedure 2

Function myFun(myVar As Double) As Double
    myFun = myVar + 1
End Function

• The module has Option Explicit at the top
• Your variables are defined within each procedure
  • The scope of the variable is the procedure
• Therefore, each variable needs to be declared within each procedure.
• Even though they have the same names, since the scope of the variable is only within the procedure, they are not the same variables.

If you want to declare a variable, and have it be the same variable in more than one procedure, you need to declare it a module level (for example).

Option Explicit
Public myVar As Double

Public Sub TestMe()
    myVar = 5
    myFun myVar
    Debug.Print myVar
End Sub

Function myFun(myVar) As Double
    myVar = myVar + 1
End Function

Note also in the two different modules, the Function and the call to the function are subtly different.

As an aside, declaring the variable with the Public keyword at the module level will make it visible to all procedures within the Project. Declaring it with the Private keyword will make it visible to all procedures in that Module.

Answer 2

You are declaring it twice, if you add Dim myVar as Double in the function myFun. The first time is with that line and the second line is in the parameters here:

Function myFun( myVar as Double) as double

That does not have anything to do with Option Explicit, you are not allowed to declare two variables with the same name in the same scope.

---

I suppose your code looks like this:

Option Explicit

Public Sub TestMe()

    'dim myVar as double (uncomment to avoid the error)
    myVar = 5
    Debug.Print myFun(myVar)

End Sub

Function myFun(myVar As Double) As Double
    myVar = myVar + 1
End Function

In order to avoid the "Not declared error", you should declare myVar in the Sub TestMe and not in the myFun function.