unbiased_rand.cpp

//Returns an integer in [0;max], where max <= RAND_MAX
int unbiased_rand(int max){
    const int rand_max = RAND_MAX - (RAND_MAX + 1) % (max + 1);
    int r;
    do
        r = rand();
    while (r > rand_max);
    return r % (max + 1);
}