NaN, Inf, isNaN, isInf – not-a-number and infinity functions
int isInf(double, int)
The IEEE floating point standard defines values called
‘not-a-number’ and positive and negative ‘infinity’.
These values can be produced by such things as overflow
and division by zero.
Also, the library functions sometimes return them when
the arguments are not in the domain, or the result is
out of range.
By default, manipulating these values may cause a floating point exception
on some processors but