递归代码：

#include 
#include 
#define MAX 5
using namespace std;int binarySearch(int x,int a[],int left,int right);int main()
{int a[MAX]={1,3,4,5,9};printf("find %d location is %d\n",4,binarySearch(4,a,0,MAX-1));printf("find %d location is %d\n",11,binarySearch(11,a,0,MAX-1));printf("find %d location is %d\n",9,binarySearch(9,a,0,MAX-1));return 0;
}int binarySearch(int x,int a[],int left,int right)
{int mid=left+(right-left)/2;if(left<=right){if(a[mid]==x)return mid;else if(a[mid]>x)return binarySearch(x,a,left,mid-1);else return binarySearch(x,a,mid+1,right);}return -1;//fail
}

分析：

注意第20行判断语句为 left<=right 

运行结果：

 非递归代码：

#include 
#include 
#define MAX 5
using namespace std;int binarySearch(int x,int a[],int left,int right);int main()
{int a[MAX]={1,3,4,5,9};printf("find %d location is %d\n",4,binarySearch(4,a,0,MAX-1));printf("find %d location is %d\n",11,binarySearch(11,a,0,MAX-1));printf("find %d location is %d\n",9,binarySearch(9,a,0,MAX-1));return 0;
}int binarySearch(int x,int a[],int left,int right)
{int mid;while(left<=right){mid = left+(right-left)/2;if(a[mid]==x)return mid;else if(a[mid]>x)right = mid-1;else left = mid+1;//mid值已经比较过了，所以进行加一减一操作去掉这一点}return -1;//fail
}

 运行结果：