a number for pi
Author
hey, i have a program where i have to convert radians to degrees. In order to do that i have to divide by pi. Instead of using the inaccurate 3.14 is there a known function or variable for pi?
thanks,
JYoung
There are a number of ways of calculating PI at runtime, such as 4*atan(1). The thing is floating point numbers don''t have a huge accuracy (around 7 digits for single precision and 15 digits for double precision), so 3.14159 or something similar is usually accurate enough for typical use.
Assuming you're using C/C++, it is pretty standard for all C/C++ compilers to have a define for pi, called M_PI, defined in math.h, so:
#include <math.h>
And then just use M_PI
eg:
double pi = M_PI;
Unless you need pi to a ridiculous number of decimal points (more than a double can hold), this works fine and is easily understood.
[edited by - gmcbay on February 7, 2003 1:32:51 PM]
#include <math.h>
And then just use M_PI
eg:
double pi = M_PI;
Unless you need pi to a ridiculous number of decimal points (more than a double can hold), this works fine and is easily understood.
[edited by - gmcbay on February 7, 2003 1:32:51 PM]
I tend to grab it & #define it from windows calculator...or any calculator I can get my hands on!
Author
double Pi = M_PI;
C:\Program Files\Microsoft Visual Studio\VC98\OpenGL\TheGrapher\main.cpp(81) : error C2065: 'M_PI' : undeclared identifier
[edited by - JYoung on February 7, 2003 3:47:49 PM]
C:\Program Files\Microsoft Visual Studio\VC98\OpenGL\TheGrapher\main.cpp(81) : error C2065: 'M_PI' : undeclared identifier
[edited by - JYoung on February 7, 2003 3:47:49 PM]
Check math.h, you have to #define some macro in MSVC to make M_PI and various other constants available.
#define my_PI 3.1415926535897932384626433832795
and you are good to go.
____________________________________________________________
Try RealityRift at www.planetrift.com
Feel free to comment, object, laugh at or agree to this. I won''t engage in flaming because of what I have said.
I could be wrong or right but the ideas are mine.
and you are good to go.
____________________________________________________________
Try RealityRift at www.planetrift.com
Feel free to comment, object, laugh at or agree to this. I won''t engage in flaming because of what I have said.
I could be wrong or right but the ideas are mine.
Here is some more digits if you care. Of course, it all depends on the resolution on your platform.
const long double gPI = 3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067982148086513282306647094;
const long double gPI = 3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067982148086513282306647094;
Sooooooo.....
if you are not satisfied with one million digits...
And you laugh at 2 million digits..
and 3 million make you yawn..
and you think 4 million digits are for girls...
..and so on...
http://www.hepl.phys.nagoya-u.ac.jp/%7Emitsuru/pi-e.html
that should satisfy even the toughest...
if you are not satisfied with one million digits...
And you laugh at 2 million digits..
and 3 million make you yawn..
and you think 4 million digits are for girls...
..and so on...
http://www.hepl.phys.nagoya-u.ac.jp/%7Emitsuru/pi-e.html
that should satisfy even the toughest...
This topic is closed to new replies.
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