There is in C99, but not in previous standards AFAIK.
In C99, you’ll have NAN and INFINITY macros.
From “Mathematics <math.h>“ (§7.12) section
The macro INFINITY expands to a constant expression of type float representing positive or unsigned infinity, if available; …
If you’re stuck with ANSI C89, you’re out of luck. See C-FAQ 14.9.