[function] Return value from a VBScript function

I have two functions, and I am trying to use the result of one function in the second one. It's going to the else part, but it's not printing anything for "cus_number".

How do I get the "cus_number" printed?

Function getNumber
    number = "423"
End Function

cus_number = getNumber

If (IsNull(cus_number)) Then
    WScript.Echo "Number is null"
Else
    WScript.Echo "cus_number : " & cus_number
End If

To return a value from a VBScript function, assign the value to the name of the function, like this:

Function getNumber
    getNumber = "423"
End Function