casting 0 to void

On my implementation of C++ (Visual Studio 2008 implementation) I see the following line in <cassert>

#ifdef  NDEBUG
#define assert(_Expression) ((void)0)

I do not understand the need to cast 0 to void. It seems to me that

#ifdef  NDEBUG
#define assert(_Expression) (0)

or even simply

#ifdef  NDEBUG
#define assert(_Expression) 0

would do, considering the contexts in which assert(expr) can be used.

So, what's the danger of 0 of type int instead of 0 of type void in this case? Any realistic examples?