VC中使用数学常量 M_PI

#include "stdafx.h"
#define _USE_MATH_DEFINES
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int _tmain(int argc, _TCHAR* argv[])
{
   printf( "An approximation of Pi is %f\n", M_PI);
   system("PAUSE");
   return 0;
}