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;
}