The fmod function returns a value f such that f has the same sign as x, the absolute value of f is less than the absolute value of y, and there exists an integer k such that:

k * y + f = x

If the quotient x / y cannot be represented, the result is undefined.

The fmod function returns the floating-point remainder of x / y.

#include <math.h>
#include <stdio.h> /* for printf */

void tst_fmod (void) {
  float f;

  f = fmod (15.0, 4.0);
  printf ("fmod (15.0, 4.0) = %f\n", f);
}