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Microsoft provides several predefined preprocessor macros for common math constants.

Syntax

#define _USE_MATH_DEFINES // for C++
#include <cmath>
#define _USE_MATH_DEFINES // for C
#include <math.h>
Remarks
The following symbols are defined for the values of their indicated expressions:
Symbol
Expression
Value
The math constants aren't defined in Standard C/C++. To use them, you must first define _USE_MATH_DEFINES, and then include <cmath> or <math.h>.
The file <ATLComTime.h> includes <math.h> when your project is built in Release mode. If you use one or more of the math constants in a project that also includes <ATLComTime.h>, you must define _USE_MATH_DEFINES before you include <ATLComTime.h>.
See also
Global constants