isinf - Macro to test for infinity

Syntax	#include <math.h> C11 int isinf(x); (End)
Description	x has to be an argument of type float, double or long double. The isinf() macro determines whether its argument is an infinity.
Return val.	Value != 0	if the value of x is +/-Infinity.
	0	otherwise.
Notes	In this implementation, isinf() always returns a value != 0, i.e. all floatingpoint numbers are finite.
See also	fpclassify, isfinite, isnan, isnormal, math.h.