//數值的正數次方
//實現函式double power（double base， int exponent），求base的exponent次方，不得使用庫函式，不需要考慮大數問題。
//注意：考慮非法輸入的返回。
#include <stdio.h>
#include <math.h>
bool Inpot_illegal = false;
bool equal(double num1, double num2)   //判斷兩數是否相等
{
	if ((num1 - num2) > -0.00001 && (num1 - num2) < 0.00001)
		return true;
	else
		return false;
}
double PowerExp(double base, int exponent)  //當指數>=0時，底數也>=0時計算
{
	if (exponent == 0)
		return 1;
	if (exponent == 1)
		return base;

	double result = PowerExp(base, exponent >> 1);
	result *= result;

	if (exponent & 0x1 == 1)
		result *= base;

	return result;
}
double Power(double base, int exponent)    //所有情況的求解
{
	Inpot_illegal = false;

	if (equal(base, 0.0) && exponent <= 0) //0的0次方及0的負數次方都是非法輸入 
	{
		Inpot_illegal = true;
		return 0.0;
	}
	int absExponent;   //取指數絕對值
	if (exponent < 0)
		absExponent = abs(exponent);
	else
		absExponent = exponent;

	double result = PowerExp(base, absExponent); //正常求解

	if (exponent < 0)   //指數小於0，則取倒數
		result = 1.0 / result;
	return result;
}
int main()
{
	int exp;
	double base, res;
	printf("請依次輸入底數和指數：");
	scanf_s("%lf %d", &base, &exp);
	res = Power(base, exp);

	if (Inpot_illegal)	//如果非法輸入，輸出error  
	{
		printf("error\n");
		return 0;
	}
	else
		printf("結果為：%f\n", res);
	return 0;
}