Re: An interesting object lesson (Ada vs C)

[Al Christians <achrist@easystreet.com>]

Jonathan Guthrie wrote:
> 
> 
> Elapsed time to my solution of the problem: 45 seconds.  Eliminate the
> warnings, and the code gives (on my computer)
> arctan 0.5 = 0.463648
> Clock ticks:  1933
> 
> > arctan 0 = 3.25435e-229
> > Clock ticks:  2160
> 
> Wow!  I've got a faster computer!  (I didn't know that was possible!
> Maybe it isn't possible.  What value of CLOCKS_PER_SEC does he
> have?  Mine is 100.)
> 
> > How did x get set to 0!?!?!?!?
> 
> It didn't.  It got DISPLAYED as 0.  That's what happens when you use
> compiler-specific extensions (as "long double" is, at least for the
> time being) without understanding the underlying mechanisms.  By the
> mechanism that printf uses to accept parameters, it had every reason to
> expect that you would pass it a double, but you passed it a long
> double.
> 

If x didn't get changed,  howcome the answers for arctan are so
different?
I put the code posted into MS VC++ v5 with the strictest warning level,
and
I got the 0.463648 answer (looks reasonable for arctan 0.5) with no
warnings
at all.  MingW32, based on GCC gives the warnings and the arctan 0
answer.

I guess that MS would probably say that you don't need to issue the
warning
if you don't drop the ball.  

This obviously has profound implications for Ada, but I won't mention
them
here for lack of interest in compiler/vendor/ .../ .../language  wars.  


Al