#include <math.h>
double fmod(double x, double y);
fmod computes the floating-point remainder of x divided by y. fmod returns the value x - n y, for some integer n such that, if y is nonzero, the result has the same sign as x and magnitude less than the magnitude of y.
If y = 0, fmod returns zero and errno is set to EDOM.
fmod(±0, y) is ±0 for y
not zero.
fmod(?, y) is NaN and raises the ?invalid?
floating-point exception.
fmod(x, 0) is NaN and raises the ?invalid?
floating-point exception.
fmod(x, ±?) is x for x
not infinite.
fmod conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).