pow.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <limits.h>

const double ERROR = 1e-8;
int doubleEQ(double x, double y)
{
	return fabs(x - y) < ERROR;
}
double myPow(double x, int n)
{
	if (n == 0) {
		return 1;
	}
	if (n == 1)
		return x;
	if (n == -1) {
		if (fabs(x - 0) < ERROR) { // x位0 1/0 没有意义
			return INT_MAX;
		}
		return 1.0 / x;
	}
	if (doubleEQ(x, 0)){
		return 0;
	}
	if (doubleEQ(x, 1)) {
		return 1;
	}
	if (doubleEQ(x, -1)) {
		if ((n & 0x1))
			return -1;
		else return 1;
	}
	if ((n & 0x1)) {
		int mid = (n - 1) / 2;
		double half = myPow(x, mid);
		return half * half * x;
	} else {
		double half = myPow(x, n / 2);
		return half * half;
	}
}
int main(int argc, char **argv)
{
	double x;
	int n;
	while (scanf("%lf%d", &x, &n)) {
		printf("%lf\n", myPow(x, n));
	}
	return 0;
}