二分查找----（返回第一个找到的值）

二分查找需要注意两个问题一个是临界问题，流行的方案是左开右闭区间方式，还有一个就是当数组元素中有多个相同待查找值的应该返回第一个，下面的代码可以解决这问题，记录一下，由于最近开始用gvim编程了，请原谅我的中式英语注释。

/*
 * binary search from programing perls
 * this binary search can solve the problem of when there are same value can not return the fisrt match number
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>


/*
 * binary search 
 * return -1 can not find the number    else the position of the number
 */

int binary_search(int in_arr[],int n,int value)
{
    int left,right,middle;
    
    left = -1,right = n;
    
    while(left + 1 != right)
    {
        middle = left + (right - left) / 2; //to prevent the overflow of the int if use middle = (right + left) / 2

        if(value > in_arr[middle])
        {
            left = middle;
        }
        else
        {// delete one compare(but can add compare times) 
            right = middle;
        }
    }

    if(right >= n || in_arr[right] != value)
    {
        right = -1;
    }

    return right;
}


int main()
{
    int i,value,in_arr[10];
    
    memset(in_arr,0,sizeof(in_arr));
    
    for(i = 0; i < 10; i++)
    {
        scanf("%d",&in_arr[i]);
    }
    
    while(1)
    {
        printf("input the value you want to find :
");
        
        scanf("%d",&value);

        int index = binary_search(in_arr,10,value);

        if(index == -1)
        {
            printf("can not find the value
");
        }
        else
        {
            printf("the %d at the position %d
",value,index);
        }
    }
    
    return 0;    
}