二分查找

#include "stdafx.h"
#include<iostream>
using namespace std;
int BinarySearch(int *a,int x);
int main()
{

	int a[17] = {1,5,7,8,9,12,15,20,32,50,78,95,101,120,130,135};
	int x = 15;
	int result = BinarySearch(a,x);
	if (result == -1) {
		std::cout<<"这数字不在此数组中"<< std::endl;
	}
	else {
		std::cout << "数字下标为：" <<result<< std::endl;
	}
    return 0;
}

int BinarySearch(int *a,int x)
{	
	
	int first = 0;
	int end = 16;
	
	while (first<end)
	{
		int mid = (first + end) / 2;
		if (a[mid] != x)
		{
			if (a[mid] > x)
			{
				end = mid - 1;
			}
			else
			{
				first = mid + 1;
			}
		}
		else
		{
			return mid;
		}
	}
	return -1;
}