#include <cstdio>
#include <vector>
#include <algorithm>
using namespace std;
void b_search( vector<int> a, int x, int size );	//二分查找函数
int main()
{
    int i, x;	/*定义循环变量和查找元素*/
    int num, n;
    vector<int> arry;	/*定义数组*/

    printf("输入元素个数: ");
    scanf("%d", &n );
    for( i=0; i<n; i++ ){
        scanf("%d", &num );
        arry.push_back( num );	/*将输入的元素压入数组末尾*/
    }
    printf("输入要查找的元素: ");
    scanf("%d", &x );
    sort( arry.begin(), arry.end() );	/*排序*/
    b_search( arry, x, arry.size() );	/*调用二分查找函数*/

    return 0;
}

void b_search( vector<int> a, int x, int size )
{
    int low, high, mid; /*定义三个查找范围控制的变量*/

    low = 0;	/*开始查找区间为整个数组*/
    high = size - 1;
    while( low <= high ){	/*循环条件*/
        mid = ( low + high ) / 2;	/*中间位置*/
        if( x == a[mid] )
            break;	/*查找成功则终止循环*/
        else if( x < a[mid] )
            high = mid - 1;	/*查找元素在前半段, high前移*/
        else
            low = mid + 1;	/*查找元素在后半段, low前移*/

    }
    if( low <= high )	/*找到则输出, 否则 则 Not Found*/
        printf("index = %d\n", mid );
    else
        printf("Not Found\n");
}