#include <math.h>
double pow(double x, double y);
pow computes x raised to the power y.
If x < 0 and y <= 0, errno
is set to EDOM and pow returns -HUGE_VAL.
If x <= 0 and y is not an integer value,
errno is set to EDOM and pow
returns -HUGE_VAL.
If y = 0, pow returns 1.
If y =1, pow returns x.
If y = NaN, pow returns NaN.
If x = NaN and y is anything other than 0,
pow returns NaN.
If x < -1 or 1 < x, and y
= +?, pow returns +?.
If x < -1 or 1 < x, and y
=-?, pow returns 0.
If -1 < x < 1 and y = +?, pow
returns +0.
If -1 < x < 1 and y = -?, pow
returns +?.
If x = +1 or x = -1 and y
= +? or y = -?, pow returns NaN.
If x = +0 and y > 0 and y
<> NaN, pow returns +0.
If x = -0 and y > 0 and y
<> NaN or y not an odd integer, pow
returns +0.
If x = +0 and y <0 and y
<> NaN, pow returns +?.
If x = -0 and y > 0 and y
<> NaN or y not an odd integer, pow
returns +?.
If x = -0 and y is an odd integer, pow
returns -0.
If x = +? and y > 0 and y
<> NaN, pow returns +?.
If x = +? and y < 0 and y
<> NaN, pow returns +0.
If x = -?, pow returns pow(-0,
y)
If x < 0 and x <> ? and y
is a non-integer, pow returns NaN.
pow conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).