Question 01:

Is there any technique where generating random number within a range is equiprobable ?

Question 02:

What is the extra advantage of the following method 02,03,04 ?

srand(time(NULL);

//Method 01: general approach

int myrand(int mod){
  return rand()%mod;
}

//Method 02: Taken form red coder submission.

int myrand(int mod) {
    int t = rand() % mod;
    t = (1LL*t*RAND_MAX + rand()) % mod;
    return t;
}

//Method 03: Taken from red coder submission.

int myrand(int mod) {
	return (int) ( (((double) rand() / RAND_MAX) * (mod) ));
}

//Method 04 : Taken from red coder submission.

inline int myrand(int mod) {
	return (((long long )rand() << 15) + rand()) % mod;
}

Updated : Idea from diko.

auto seed = chrono::high_resolution_clock::now().time_since_epoch().count();
std::mt19937 mt(seed);

int myrand(int mod) {
    return mt()%mod;
}