fmod取余数

    // wrapping angle to [-pi .. pi]
    angle_increment = fmod(angle_increment + 5*M_PI, 2*M_PI) - M_PI;

     double fmod (double numer     , double denom);
      float fmod (float numer      , float denom);
long double fmod (long double numer, long double denom);
     double fmod (Type1 numer      , Type2 denom);       // additional overloads

/* fmod example */
#include <stdio.h>      /* printf */
#include <math.h>       /* fmod */

int main ()
{
  printf ( "fmod of 5.3 / 2 is %f\n", fmod (5.3,2) );
  printf ( "fmod of 18.5 / 4.2 is %f\n", fmod (18.5,4.2) );
  return 0;
}