Calculates a power of floating-point number.
double pow (double x, double y);
float powf (float x, float y);
long double powl (long double x, long double y);
x Value to be raised to a power
Normal: Value of x raised to the power y
Abnormal: Domain error: Returns not-a-number.
A domain error occurs if x is 0.0 and y is 0.0 or less, or if x is negative and y is not an integer.