isnan,isnanf,isinf,isinff,finite,finitef---test for exceptional numbers

#include <ieeefp.h>
int isnan(double arg);
int isinf(double arg);
int finite(double arg);
int isnanf(float arg);
int isinff(float arg);
int finitef(float arg);

There are five major number formats -

zero

a number which contains all zero bits.

subnormal

Is used to represent number with a zero exponent, but a non zero fraction.

normal

A number with an exponent, and a fraction

infinity

A number with an all 1's exponent and a zero fraction.

NAN

A number with an all 1's exponent and a non zero fraction.

isnan returns 1 if the argument is a nan. isinf returns 1 if the argument is infinity. finite returns 1 if the argument is zero, subnormal or normal. The isnanf, isinff and finitef perform the same operations as their isnan, isinf and finite counterparts, but on single precision floating point numbers.