   Is there a function in the standard library for PI?
  (Using C++) I'm trying to clean up my code a bit, and I tried to put PI() in place of 3.14159 (I guess I'm used to working with spreadsheets) and it didn't work.  I included cmath already.  If there isn't should I define it at the beginning or just leave the number in place in the code?   
  PI in C(++) is a constant (so no function), called M_PI. It's defined in <math.h> or <cmath> as you already guessed.;  I think PI is defined as the constant M_PI.   ;  #define PI 3.14159265   ;  Thank you for the quick replies.Edit: Hmm that didn't work.  Any possible reasons why M_PI won't work for me?  I'm using VS 2005 EE.   ;  Mmmm, yep... for some reason unknown to me, Microsoft compilers won't define M_PI until you do:#define _USE_MATH_DEFINESbefore including cmath.   ;  If you poke around in the MSVC++ 2005 headers you'll see the various maths constants (like M_PI) need _USE_MATH_DEFINES defined before you include cmath.  This is done because aparently these constants are not part of the standard (I read that in a comment in one of the headers).   ;  As the anymous poster posted, your're not going to get any deeper with3.1415926535897932384626433832795...#define pi 3.141592653589especially since floating point values cut so much out.   ;  M_PI and its ilk aren't actually part of the C standard, which explains the need for the #defines.Regardless, its better that headers use as few macros as possible by default (especially for things like pi...and min and max) to minimize collisions and weirdness.   ;  Ok, thanks.  Since its not part of the C++ standard, I guess I'll just do a regular define.I have two more questions.  I got a warning for using itoa.  The warning told me itoa is not part of the standard anymore (?) and to use _itoa.  When I changed it, it told me I need to use _itoa_s (why didn't it say that the first time?).  Anyway my question is whether I should continue using _itoa_s because that is the standard.  I was using the Dev C++ IDE before and had no problems with using just itoa.Another question is I got a warning for something I didn't even write.  It had to do with code in the include file xlocnum.  Has anyone had this warning happen to them?   