fmod() - floating-point remainder function
#include <math.h>
double fmod (double x, double y)
The fmod(3) function computes the floating-point remainder of x/y.
The fmod(3) function returns the value x - i * y, for some integer i such that, if y is non-zero, the result has the same sign as x and magnitude less than the magnitude of y. If y is zero, whether a domain error occurs or the fmod(3) function returns zero is implementation-defined.