数值的平方

注意:
1. 指数为负数的情况
2. 对 0 求倒数的情况
3. 判断两个符点数是否相等不能用等号

思路：求一个数的n 次方可以采用递归的思想
如：求 2^32 => 求 (2^16) 的平方。
而求 2^16 => 求 (2^8) 的平方。
总结如下：

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#include <iostream>using namespace std;bool g_InvalidInput = false;    // 用于区分是否输入的值有错误bool equal(double n1, double n2){    if(n1 - n2 > -0.0000001 && n1 - n2 < 0.0000001)        return true;    else        return false;}double PowerWithUnsignedExponent(double base, unsigned int exponent){    double result = 1.0;    for(int i = 1; i <= exponent; i++)        result *= base;    return result;}double PowerWithUnsignedExponent1(double base, int exponent){    if(exponent == 0)        return 1;    if(exponent == 1)        return base;    double result = PowerWithUnsignedExponent1(base, exponent>>1);    result *= result;    if(exponent & 0x1)        result *= base;    return result;}double Power(double base, double exponent){    if(equal(base,0.0) && exponent < 0){        g_InvalidInput = true;        return 0.0;    }    unsigned int absExponent = (unsigned int) exponent;    if(exponent < 0)        absExponent = (unsigned int) -exponent;    double result = PowerWithUnsignedExponent1(base, absExponent);    if(exponent < 0)        return 1.0 / result;    return result;}int main(int argc, const char * argv[]) {    double result = Power(2, -3);    double result1 = Power(0, 0);    if(g_InvalidInput == true)        cout<<"您输入的数值有误"<<endl;    else        cout<<result;    return 0;}