C Interview Questions and Answers


The predefined constant M_PI seems to be missing from my machines copy of math.h.

That constant (which is apparently supposed to be the value of pi, accurate to the
machine's precision), is not standard; in fact a standard-conforming copy of
should not #define a symbol M_PI. If you need pi, you'll have to define it
yourself, or compute it with 4*atan(1.0) or acos(-1.0). (You could use a construction

#ifndef M_PI

#define M_PI 3.1415926535897932385


to provide your own #definition only if some system header file has not.)

Posted by:Richards