C/math.h/nan
nan: returns a value that is not a number and that contains *content
<source lang="cpp">
//Declaratin: float nanf(const char *content);
double nan(const char *content); long double nanl(const char *content); #include <math.h> #include <stdio.h> int main(void) { double f; f = nan("2.0"); printf("%f " , f); } /* -1.#IND00 */ </source>