double modf(double x, double *iptr)
float modff(float x, float *iptr)
long double modfl(long double x, long double *iptr) [V2.01.00 or later]
These functions divide x into integral and fractional parts. They return the fractional part and store the integral part in the object pointed to by iptr.
Both the integral part and fractional part have the same sign as x.