i don't know if you're trying to be funny...
but what's between the definition of N1 and the undef of A may be a very
complex. it's just simplified for demonstration.
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> Date: Sun, 1 Jan 2012 00:42:16 -0500
> From: de...@adacore.com
> To: ren_zokuke...@hotmail.com
> CC: gcc@gcc.gnu.org
> Subject: Re: a nifty feature for c preprocessor
>
> On 12/31/2011 4:44 AM, R A wrote:
> >
> > alright, here's another example why eval is a good idea:
> >
> > #define A 17
> > #define B 153
> > #define N1 ((A + B)/2) /* intended was (17 + 153)/2 */
> >
> > #undef A
> > #define A 230
> > #define N2 ((A + B)/2) /* intended was (230 + 153)/2 */
>
> Bad example, this is a misuse of the preprocessor in any case!
