fmod(x,y) - Calculates x modulo y, the remainder of x/y.
This function is the same as the modulus operator. But fmod() performs floating point divisions.

Example:

#include <stdio.h>
#include <math.h>

int main ()
{
  printf ("fmod of 5.5 by 1.3 is %lf\n", fmod (5.5, 1.3) );
  return 0;
}

Output:
fmod of 5.5 by 1.3 is 0.300000