I came a bit late to this, but this is something like what I might expect to see in C++.

// Interface defined by the problem statement has been adjusted
size_t get_num_of_ints( const int* arr, size_t r, int N, size_t* first )
{
    std::pair<const int *, const int *> range = std::equal_range(arr, arr+r, N);
    size_t count = range.second - range.first;
    if (count > 0 && first != 0)
        *first = range.first - arr;
    return count;
}

I think the interface is broken as defined, so I've fixed it :)

I came a bit late to this, but this is something like what I might expect to see in C++.

// Interface defined by the problem statement has been adjusted
size_t get_num_of_ints( const int* arr, size_t r, int N, size_t* first )
{
    std::pair<const int *, const int *> range = std::equal_range(arr, arr+r, N);
    size_t count = range.second - range.first;
    if (count > 0 && first != 0)
        *first = range.first - arr;
    return count;
}

I think the interface is broken as defined, so I've fixed it :)