Determines whether its argument has a finite value (zero, subnormal, or normal).
int isfinite(real-floating x); (C99)
If the argument is finite (0, subnormal number, or normal number), a value other than 0 is returned.
If the argument is infinite or NaN, 0 is returned.
This macro determines whether its argument has a finite value (zero, subnormal, or normal).
If a type other than the floating-point type is passed to the argument, correct operation is not guaranteed.