Procedure with Optional Parameters in Excel VBA

The UserName() function returns a string consisting of the first name and last name specified as its parameter values. If one of the parameters is omitted, it returns an incomplete name.

When working with optional parameters, you must use the IsMissing() function, which returns True if the corresponding parameter was not passed to the procedure, and False otherwise.

Function procedure with optional parameters

Function UserName(Optional LastName As String, _
                  Optional FirstName As String) As String
    If Not (IsMissing(LastName)) And Not (IsMissing(FirstName)) Then
        UserName = LastName & Space(1) & FirstName
    ElseIf IsMissing(LastName) And Not (IsMissing(FirstName)) Then
        UserName = FirstName
    ElseIf Not IsMissing(LastName) And IsMissing(FirstName) Then
        UserName = LastName
    End If
End Function

Demonstration of using the function:

Sub DemoUserName()
    MsgBox UserName(LastName:="Bond", FirstName:="James")
    ' Bond James
    MsgBox UserName("James", "Bond")
    ' James Bond
    MsgBox UserName("Bond")
    ' Bond
    MsgBox UserName(, "James")
    ' James
    MsgBox UserName()
    ' Nothing
End Sub