VBA Function Optional parameters - vba

Question

I am calling a specific piece of code several times therefore I would like to use optional parameters.
I can write something like:
Public Sub main()
strA = "A"
'Calling the function
CalculateMe (strA)
End Sub
Public Sub CalculateMe(strA As String)
Set rs = DB.OpenRecordset("tbl_A")
rs.MoveFirst
Do Until rs.EOF
If rs.Fields(0) = strA Then
dblA = rs.fields(2).Value
End If
rs.MoveNext
Loop
End Sub
How can I change the function to hold more than 1 optional parameters?
Something like:
Public Sub main()
strA = "A"
strB = "B"
'Calling the function
CalculateMe (strA, strB)
more code
End Sub
Public Sub CalculateMe(Optional strA As String, Optional strB as String)
Set rs = DB.OpenRecordset("tbl_A")
rs.MoveFirst
Do Until rs.EOF
If rs.Fields(0).Value = strA And rs.Fields(1).Value = strB Then
dblA = rs.Fields(2).Value
End If
rs.MoveNext
Loop
End Sub
Following Pankaj Jaju's advice, I have managed to have it run by changing it to:
Public Sub main()
strA = "A"
strB = "B"
'Calling the function
dblA = CalculateMe (strA, strB)
End Sub
Public Function CalculateMe(Optional ByVal strA As String, Optional ByVal strB as String)
Set rs = DB.OpenRecordset("tbl_A")
rs.MoveFirst
Do Until rs.EOF
If rs.Fields(0).Value = strA And rs.Fields(1).Value = strB Then
dblA = rs.Fields(2).Value
End If
rs.MoveNext
Loop
End Sub
Now, how can I clear the value of an optional parameter? I will need this for some of the calculations. Something like:
Set strA = Nothing

Answer 1

Change your sub and add ByVal
Public Sub CalculateMe(Optional ByVal strA As String, Optional ByVal strB As String)

Answer 2

Public Sub CalculateMe(Optional varA As Variant, Optional varB as Variant)
Excerpts from Chip Pearson's excellent explanation:
Rules governing the use of optional parameters:
The Optional keyword must be present to make a parameter optional.
The data type should be (but need not be, see below) a Variant data
type.
The optional parameter(s) must be at the end of the parameter
list.
The IsMissing function will work only with parameters declared
as Variant. It will return False when used with any other data type.
User defined types (UTDs) cannot be optional parameters.
Example
Function Test(L1 As Long, L2 As Long, _
Optional P1 As Variant, Optional P2 As Variant) As String
Dim S As String
If IsMissing(P1) = True Then
S = "P1 Is Missing."
Else
S = "P1 Is Present (P1 = " & CStr(P1) & ")"
End If
If IsMissing(P2) = True Then
S = S & " " & "P2 Is Missing"
Else
S = S & " " & "P2 Is Present (P2 = " & CStr(P2) & ")"
End If
Test = S
End Function
Here, both L1 and L2 are required but P1 and P2 are optional. Since both are Variant types, we can use IsMissing to determine whether the parameter was passed in. IsMissing returns True if the Variant parameter is omitted, or False if the Variant parameter is included. If the data type of the optional parameter is any data type other than Variant, IsMissing will return False.

Answer 3

Instead of CalculateMe(,strB) you can use
dblA = CalculateMe strB:="B"

Answer 4

I'm not sure you really mean "optional". In your example, you're listing the args as optional, but you're still passing both arguments to the function.
In any case, here you pass both arguments:
Public Sub main()
strA = "A"
strB = "B"
'Calling the function
dblA = CalculateMe(strA, strB)
more code
End Sub
If you want to pass only one of the arguments, then do like:
dblA = CalculateMe(, strB)
Or:
dblA = CalculateMe(strA)
Otherwise, if you are always passing both arguments, then it doesn't make sense to have them Optional.