#include <math.h> double exp(double x);
exp computes the base-e exponential of x.
If |x| >~ 709.782, errno is set to EDOM and exp returns HUGE_VAL.
If x is NaN, exp returns NaN.
If x is ?, exp returns ?
If x is -?, exp returns 0.
exp conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).