二分查找：

二分查找又称折半查找，优点是比较次数少，查找速度快，平均性能好；其缺点是要求待查表为有序表，且插入删除困难。

代码不多也就几行；主要 start = 0； end = nLength -1;while(start <= end);

#include <iostream>

using namespace std; 
/* run this program using the console pauser or add your own getch, system("pause") or input loop */

int bianrySearch(int a[], int nLength, int val)
{
	int start = 0;
	int end = nLength - 1;
	int index = -1;
	while(start<=end)
	{
		index = (start+ end)/2;
		if(a[index] == val)
		{
			return index;
		}
		else if(a[index] < val)
		{
			start = index + 1;
		}
		else
		{
			end = index -1;
		}
	}
	
	return -1;
}

int main(int argc, char** argv) {
	
	int a[] = {0,1,2,3,4,5};
	for(int i = 0; i < 6; i++)
	{
		cout<<a[i]<<"";
	}
	int k =bianrySearch(a,sizeof(a)/sizeof(int),5);
	cout<<"5在的位置为：";
	cout<<k<<endl;
	return 0;
}