Filling an array with random numbers from 1 to 10^10 in C or C++

Question

a part of an assignment of mine is based on an array (its size is given by the user) which contains random numbers from 1 to 10^10. Then we have to find the k-th smaller number

Answer 1

long long get_big_rand()
{

    long long result;
    do {
        result = (rand() & 0x3ff);
        result <<= 12;
        result |= (rand() & 0xfff);
        result <<= 12;
        result |= (rand() & 0xfff);
    } while (++result > 10000000000ULL);
    return result;
}