数值的整数次方

思路：
方法一：指数exponent为负，需要把exponent变为正数，然后再对base^(-exponent)取倒数；当exponent为负数时，还需考虑base为0的情况;double和0相等的判断。

double Power(double base,int exponent){
       double result=0.0;
       if(equal(0.0,base)&&exponent<0)
                return -0.1;
       if(exponent<0)
               result= PowerWithPosExponent(base,-exponent);
               result=1/result;
       if(exponent>=0)
               result= PowerWithPosExponent(base,exponent);            
}
double PowerWithPosExponent(double base,int exponent){
       double result=1.0;
       for(int i=1;i<=exponent;i++){
              result*=base;
       }
}
boolean equal(double num1,double num2){
      if(num1-num2>-0.000001&&num1-num2<0.000001)
              return true;
      return false;
} 

方法二：递归

Paste_Image.png

double Power(double base,int exponent){
     if(exponent==0)
           return 1;
     if(exponent==1)
           return base;
     double result=Power(base,exponent>>1)
           result*=result;
      if(base&0x1==1)
           result*=base;
      return result;
}