核心代码（循环）; 
	int f= -1;
	while(left<=right){
		mid=(left+right)/2;
		if(a[mid]==key){
			f=mid;
			break;
		}
		if(key<a[mid]) r=mid-1;
		if(key>a[mid]) l=mid+1;
	}
	if(f==-1) cout<<"没找到";
	else cout <<f<<endl;

核心代码(递归):
int binsearch(int left,int right){
	if(left<=right){
		int mid=(left+right)/2;
		if(a[mid]==key) return mid;
		if(key<a[mid]) return binsearch(left,mid-1);
		if(key>a[mid]) return binsearch(mid+1,right);
	}
	else return 0;
} 

例题
输入n和n个整数，使用冒泡排序将其从小到大排序，输出排序前和排序后的结果

#include<iostream>
using namespace std;
int main(){
	int n;
	cin>>n;
	int a[n];
	for(int i=0;i<n;i++){
		cin>>a[i];
	}
	int key;
	cin>>key;
	int l=0;int r=n-1;
	int mid;
	int f= -1;
	while(l<=r){
		mid=(l+r)/2;
		if(a[mid]==key){
			f=mid;
			break;
		}
		if(key<a[mid]) r=mid-1;
		if(key>a[mid]) l=mid+1;
	}
	if(f==-1) cout<<"没找到";
	else cout <<f<<endl;
	}