When you already have a SDK Help, you will surely notice that functions return values and parameters have some strange types like VOID, LPCSTR or DWORD. If you are familiar with C, then you know what they mean. For the rest, here is a table taken from VB Books Online (topic is Converting C Declarations to Visual Basic):

C language data type	In Visual Basic declare as	Call with
ATOM	ByVal variable As Integer	An expression that evaluates to an Integer
BOOL	ByVal variable As Long	An expression that evaluates to a Long
BYTE	ByVal variable As Byte	An expression that evaluates to a Byte
CHAR	ByVal variable As Byte	An expression that evaluates to a Byte
COLORREF	ByVal variable As Long	An expression that evaluates to a Long
DWORD	ByVal variable As Long	An expression that evaluates to a Long
HWND, HDC, HMENU, etc.	ByVal variable As Long	An expression that evaluates to a Long
INT, UINT	ByVal variable As Long	An expression that evaluates to a Long
LONG	ByVal variable As Long	An expression that evaluates to a Long
LPARAM	ByVal variable As Long	An expression that evaluates to a Long
LPDWORD	variable As Long	An expression that evaluates to a Long
LPINT, LPUINT	variable As Long	An expression that evaluates to a Long
LPRECT	variable As type	Any variable of that user-defined type
LPSTR, LPCSTR	ByVal variable As String	An expression that evaluates to a String
LPVOID	variable As Any	Any variable (use ByVal when passing a string)
LPWORD	variable As Integer	An expression that evaluates to an Integer
LRESULT	ByVal variable As Long	An expression that evaluates to a Long
NULL	As Any or ByVal variable As Long	ByVal Nothing or ByVal 0& or vbNullString
SHORT	ByVal variable As Integer	An expression that evaluates to an Integer
VOID	Sub procedure	Not applicable
WORD	ByVal variable As Integer	An expression that evaluates to an Integer
WPARAM	ByVal variable As Long	An expression that evaluates to a Long

Notes:

You should notice that the BOOL type (boolean) evaluates to Long and not Boolean. So, 0 refers to False and any other value to True.

HWND, HDC, HMENU, etc. - etc. means there are also other types like these. All of them begin with H and stand for handles for different type of objects. For example HBITMAP is a bitmap handle, HBRUSH is a brush handle and so on. They all evaluate to Long and should be passes ByVal.

Notice also that LPVOID is declared as variable As Any. There is a separate topic dedicate to Any.

Some types begin with LP. It is an abbreviation of Long Pointer to. So LPWORD is actually a memory location where the data is stored. No, you won't have to call a function to get this address. When you pass your argument ByRef (the default) you actually pass its address. The thing to remember here is that, if you parameter type begins with LP - you should pass it ByRef. By the way LPARAM is like Lparam and not LParam. It is not a pointer. You must pass the actual value here, so it is passed ByVal.

There is also some strange type NULL. You know from VB so I won't discuss it here. Just choose a way you will pass it when needed. In most of the cases I see passing it as ByVal 0& or as vbNullString.

And lastly, VOID is used for functions return value to specify that there is no such value. API does not have Subs so this is the way it implements them. Just remember - if the function is declared as VOID - you must declare it as Sub in your VB code.

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Copyright (c) 1998, Billy&George Software and Peter Dimitrov
Revised March 2000