如何编译 “折半法查找”

/*---------------------------------------------------------------------------
File name: binary_search.c
Author: HJin (email: fish_sea_bird [at] yahoo [dot] com )
Created on: 7/5/2007 15:04:19
Environment: Windows XP Professional SP2 English +
Visual Studio 2005 v8.0.50727.762

Modification history:
===========================================================================

*/

#include <stdio.h>

#define DIM(x) sizeof((x))/sizeof((x)[0])

/** Binary search.

Pre-condition: the array a is sorted, either
ascending (1 2 3 4 5) or descending (5 4 3 2 1).

Post-condition: return the index of the search key.
*/
int binary_search(int* a, unsigned int n, int key)
{
int low = 0, high= n-1, mid;

if(n<1)
{
printf("invalid input for n.\n");
return -1;
}

if(a[0]<=a[n-1]) /// the array is sorted ascending
{
while(low<=high) /// don't forget =
{
mid=(high+low)/2;

if(a[mid]<key)
low=mid+1;
else if(a[mid]>key)
high=mid-1;
else
return mid;
}
}
else /// the array is sorted descending
{
while(low<=high) /// don't forget =
{
mid=(high+low)/2;

if(a[mid]<key)
high=mid-1;
else if(a[mid]>key)
low=mid+1;
else
return mid;
}
}

return -1;
}

int main()
{
int a[]={-4, -2, -1, 0, 2, 7, 9, 11};

int i=binary_search(a, DIM(a), 0);

printf("i = %d\n",i);

return 0;
}