vb6gotchas.vb

' apostrophes denote comments
REM keyword also does this

' VB6 is case insensitive

Option Explicit
' this ensures that you only use variables you have declared
' (avoiding typos creating new variables)


Dim X, Y, Z As Integer
' Integers are only 16-bit. Use Long instead
' X and Y are Variants, only Z is an integer

If X = 1 Then
    X = 2 ' = is overloaded for comparison and assignment
    Dim S As Long
End If
' variables have only function/sub level scope. S is still
' accessible here
S = 0

' null keyword is Nothing

Dim AnArray(3) As Boolean
' this creates a FOUR element array numbered 0-3
Dim AnotherArray(-5 To 10)
' we can also define arbitrary array bases

Call DoStuff(X, Y, Z) ' call keyword requires brackets
DoStuff X, Y, Z ' without call we may not use brackets
S = DoStuff(X, Y, Z) ' unless we are returning a value

Dim Obj As Object
Set Object = GetSomeObject("foo") ' set is compulsory for reference assignment
Let X = 2 ' let is completely optional for primitives

Dim foo As String
foo = "escape strings with "" (double quotation marks)"
foo = "append with ampersand " & foo

X = 1 / 2 ' floating point division
X = 3 \ 2 ' integer division

Private Sub Foo(ByVal A As Integer, ByRef B As String)
    ' arguments are passed by reference as default!

    On Error GoTo Panic
    ' yes, goto is available

    If A <> 0 And Test(A) Then ' not equal to zero
      ' Boolean logic does not use short circuiting
    ' so Test(A) is always evaluated
      Exit Sub
   End If

Panic:
   Debug.Print "Do you know where your towel is?"
End Sub

Function Bar() As Integer
    ' subs may not return values
    ' they are optional for functions
End Function

Public Sub Thing_CrazyEvent() As Integer
    ' by convention this code is called when the CrazyEvent event
    ' occurs to Thing

    Dim i As Long
    ' vb6 ide has a habit of changing the capitalisation based on
    ' variable names elsewhere
    For I = 2 To 20 Step 2
	MsgBox I
    Next I ' stating variable here is optional but
    ' if you do the compiler will check it

    Dim N As ListItem
    For Each N In List
	' for each loops are also available
	DoSomething N
    Next
End Function

Private Sub Something(A As String, B As String, C As String, _
		      D As String)
    ' line continuations are available using _ but they are capped at 25 lines
    ' this is a pain for sql, see http://www.dailydoseofexcel.com/archives/2005/04/18/line-continuation-limit/
End Sub

Implements AnInterfaceName
' vb objects can only use interface inheritance
' not implementation inheritance

' objects also do not support constructor methods