#include <stdio.h>
#include <math.h>
int binary_search(int arr[],int k,int sz)
{
    int left = 0;
    int right = sz-1;

    while(left <= right)
    {    
        int mid = (left+right)/2;
    if(arr[mid] < k)
    {
            left = mid+1;
    }
    else if( arr[mid] > k)
    {
            right = mid-1;
    }
    else
    {
        return mid;
    }
    }
    return -1;
}

int main() {
    int arr[]={0,1,2,3,4,5,6,7,8,9,10};
    int k=7;
    int sz = sizeof(arr)/sizeof(arr[0]);
    int ret = binary_search(arr,k,sz);
    if(ret==-1)
        printf("找不到%d",k);
    else
        printf("找到了下标是：%d",ret);
	return 0;
}