Algorithm for creating an array of 5 unique integers between 1 and 20

Question

My goal is creating an array of 5 unique integers between 1 and 20. Is there a better algorithm than what I use below?

It works and I think it has a constant time complexity due to the loops not being dependent on variable inputs, but I want to find out if there is a more efficient, cleaner, or simpler way to write this.

int * getRandom( ) {

  static int choices[5] = {};
  srand((unsigned)time(NULL));
   
  for (int i = 0; i < 5; i++) {

    int generated = 1 + rand() % 20;
    for (int j = 0; j < 5; j++){
      if(choices[j] == generated){
        i--;
      }
    }
    
    choices[i] = generated;
    cout << choices[i] << endl;
  }

  return choices;
}

Thank you so much for any feedback. I am new to algorithms.

Answer 1

The simplest I can think about is just create array of all 20 numbers, with choices[i] = i+1, shuffle them with std::random_shuffle and take 5 first elements. Might be slower, but hard to introduce bugs, and given small fixed size - might be fine.

BTW, your version has a bug. You execute line choices[i] = generated; even if you find the generated - which might create a copy of generated value. Say, i = 3, generated is equal to element at j = 0, now your decrement i and assign choices[2] - which becomes equal to choices[0].