#include <iostream>

using namespace std;

const int NOT_FOUND{-1};

int BinarySearch(int array[], int start, int end, int key) ;

int main() {
    int array[]{1,5,9,12,15,17,21,30};

    for(int i =0; i < 33; ++i) {
        int pos = BinarySearch(array,0, 7, i);
        if (pos == NOT_FOUND) {
           cout << i << " was not found" << endl;
        } else {
           cout << i << " was found at " << pos  << endl;
        }
    }

    return 0;
}
int BinarySearch(int array[], int start, int end, int key) {
    int mid;

    if (start > end) {
       return NOT_FOUND;
    }

    mid = (start + end)/2;
    if(array[mid] == key) {
       return mid;
    } else if (array[mid] < key)  {
       return BinarySearch(array, mid+1, end, key);
    } else {
       return BinarySearch(array, start, mid-1, key);
    }

}