C/math.h/nan
nan: returns a value that is not a number and that contains *content
//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
*/