Metrologic Optimus S Programming Manual page 229

modf (x, double
split x into its integer and fraction parts, each with the same sign
*ip)
as x. Returns the fractional part and loads the integer part into
*ip.
fmod (x, y)
the remainder of x/y, with the same sign as x.
If y = 0, the result is implementation-defined.
Chapter 4 Standard Library Routine 223