From: Hans-Bernhard Broeker <broeker AT physik DOT rwth-aachen DOT de>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: M_PI and -ansi
Date: 18 Jun 2001 17:21:09 GMT
Organization: Aachen University of Technology (RWTH)
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Patrick Mitran <pmitran AT tsp DOT ece DOT mcgill DOT ca> wrote:
> Hi,

> when I compile with the -ansi switch, it seems that I don't have a
> predefined constant for PI in math.h.

As the old saying goes: "Well, don't do that, then!". In this case:
don't use -ansi unless you positively have to.

> What would be a good way of getting a numerically accurate value of
> PI that is ANSI compliant?

#include <math.h>

const double pi = 4*atan(1.0);

That's about as portable as it gets, and as numerically accurate as
anything else you'll be doing in the same instance of the program,
using the same C math library implementation.
-- 
Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de)
Even if all the snow were burnt, ashes would remain.