Question

I’m implementing the binary search algorithm in C++, but the algorithm isn’t returning the correct value. The code can be found here.

template<class T>
int binary_search(T search_value, T search_array[]) {

    int mid; /* The middle element of the remaining array to be searched. */
    int min = 0; /* The first index of the array. */
    /* This forumla gives us the size of the array. */
    int max = sizeof(search_array)/sizeof(search_array[0]);

    /* Continue searching until min >= max. */
    while (min < max) {
        /* Compute the value of mid using a formula that won't produce a number
         * larger than the maximum allowed value of an integer. */
        mid = (max-min)/2 + min;

        /* Depending the whether search_value is larger or smaller than the
         * value of whatever is at search_array[mid], set one of mid and max
         * equal to mid. */
        if (search_value > search_array[mid])
            min = mid + 1;
        else if (search_value < search_array[mid])
            max = mid + 1;
        else {
            return mid;
        }
    }

    return -1;
}

Given an array {0, 1, 3, 5, 7, 9} and searching for 3, the function should return 2, the index of 3 in the array. My function is returning -1 though, which means 3 was not found in the array. Where’s the problem?

Answer 1

int max = sizeof(search_array)/sizeof(search_array[0]);

This approach is not good to compute the size of the array, it works only in the function where you create your array.

Pass the size of your array as a parameter of your function, it’s the easiest approach.