(C++) Making a random sequence of a set of numbers 1-3 - c++

Question

I need my program to make a random sequence from 1-3 each time, but I don't understand how I'd use rand() to make the sequence of numbers 1 to 3 in a different order each program. It can't be the same number again, so I don't know what I'd do to prevent that. An example run would be
123 the first, 231 the second, 321 and so fourth
What would you use to make a sequence that doesn't repeat numbers

Answer 1

The simplest way to generate your sequence would be to use std::shuffle to re-order a vector containing your desired values:
#include <vector>
#include <algorithm>
#include <random>
#include <iostream>
int main()
{
std::random_device rd;
std::mt19937 g(rd());
std::vector<int> elements = { 1, 2, 3 };
std::shuffle(elements.begin(), elements.end(), g);
for (int i : elements)
{
std::cout << i << "\n";
}
}
If you really must use rand() (its not generally a very good random number generator) you can just about squeeze it into shuffle too:
#include <vector>
#include <algorithm>
#include <ctime>
#include <iostream>
struct RandDevice
{
using result_type = uint32_t;
static result_type max() { return static_cast<result_type>(RAND_MAX); };
static result_type min() { return 0; };
result_type operator()() {
return static_cast<result_type>(rand());
}
};
int main()
{
std::vector<int> elements = { 1, 2, 3 };
srand(time(0));
std::shuffle(elements.begin(), elements.end(), RandDevice());
for (int i : elements)
{
std::cout << i << "\n";
}
}

Answer 2

You can use std::next_permutation
Example here : https://en.cppreference.com/w/cpp/algorithm/next_permutation

Answer 3

it's pretty easy to do.. just compare the number you with every occupied element in the array. if it is not in the array, add to array. else, try again.
I have done similar code check this out
#include <iostream>
#include <ctime>
#include <cstdlib>
using namespace std;
void displayArray(int randNum[], int elements);
void randomNum(int randNums[], int elements);
int main ()
{
//declare array
int numbers[999] = {0};
//random number generator
srand(static_cast<int>(time(0)));
randomNum(numbers, 999);
displayArray(numbers, 999);
system("pause");
return 0;
}
void randomNum(int randNums[], int elements)
{
for (int i = 0; i < elements; i++)
{
bool same;
do
{
same = false;
randNums[i] = rand() % 999 + 100;
// Check if the newly generated number is a duplicate:
for (int check = 0; check < i; check++)
{
if (randNums[i] == randNums[check])
{
same = true;
break;
}
}
} while (same);
}
}
void displayArray(int randNum[], int elements)
{
for (int sub = 0; sub < elements; sub ++)
{
cout << "Unique Numbers: " << randNum[sub] << endl;
}
}