C++ 二分查找

#include <iostream>
using namespace std;

int BinarySearch(int a[], int length, int value) {
    if(a == NULL || length <= 0) return -1;
	int st = 0;
	int end = length - 1;
	while(st <= end) {
        int mid = (st + end) >> 1;
        if(a[mid] > value) {
            end = mid - 1;
        } else if(a[mid] < value) {
            st = mid + 1;
        } else {
            return mid;
        }
	}
	return -1;
}

int main() {
    int a[6] = {1,2,3,4,5,6};
    int res = BinarySearch(a,6,12);
    cout<<res;
}