新手求问一个折半查找的问题

[IT保安]

#include <iostream>
#include <string>

using namespace std;

int BinaryS(int *source,int dest,int number); //折半查找

int main()
{
	int s[12] = {1,2,3,4,5,6,7,8,9,10,11,12};

	//int num = BinaryS(s,22,12);

	cout << "数字11在哪个位置呢?\n";
	cout << BinaryS(s,11,12) << endl;

	return 0;
}
int BinaryS(int *source,int dest,int number)
{
	int left = 0;
	int right = number - 1;
	while(left <= right)
	{
		int middle = (right - left)/2;
		if( dest < source[middle])
			right = middle - 1;
		else if (dest > source[middle])
			left = middle + 1;
		else
		//if( dest == source[middle])
			return middle;
		
	}

	return -1;
}

根据我写的代码，如果用前半段的数字测试，一切正常，如果用后半段的数字测试，就无法显示了，好像就陷在while里面出不来了，弄不明白！

[万俟宇轩]

同一楼！middle的赋值语句右边应该是左加右除以2

[赵4老师]

参考C:\Program Files\Microsoft Visual Studio\VC98\CRT\SRC\BSEARCH.C

/***
*bsearch.c - do a binary search
*
*       Copyright (c) 1985-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
*       defines bsearch() - do a binary search an an array
*
*******************************************************************************/

#include <cruntime.h>
#include <stdlib.h>
#include <search.h>

/***
*char *bsearch() - do a binary search on an array
*
*Purpose:
*       Does a binary search of a sorted array for a key.
*
*Entry:
*       const char *key    - key to search for
*       const char *base   - base of sorted array to search
*       unsigned int num   - number of elements in array
*       unsigned int width - number of bytes per element
*       int (*compare)()   - pointer to function that compares two array
*               elements, returning neg when #1 < #2, pos when #1 > #2, and
*               0 when they are equal. Function is passed pointers to two
*               array elements.
*
*Exit:
*       if key is found:
*               returns pointer to occurrence of key in array
*       if key is not found:
*               returns NULL
*
*Exceptions:
*
*******************************************************************************/

void * __cdecl bsearch (
        REG4 const void *key,
        const void *base,
        size_t num,
        size_t width,
        int (__cdecl *compare)(const void *, const void *)
        )
{
        REG1 char *lo = (char *)base;
        REG2 char *hi = (char *)base + (num - 1) * width;
        REG3 char *mid;
        unsigned int half;
        int result;

        while (lo <= hi)
                if (half = num / 2)
                {
                        mid = lo + (num & 1 ? half : (half - 1)) * width;
                        if (!(result = (*compare)(key,mid)))
                                return(mid);
                        else if (result < 0)
                        {
                                hi = mid - width;
                                num = num & 1 ? half : half-1;
                        }
                        else    {
                                lo = mid + width;
                                num = half;
                        }
                }
                else if (num)
                        return((*compare)(key,lo) ? NULL : lo);
                else
                        break;

        return(NULL);
}

[zilaishuichina]

int middle = (right + left)/2;