an combination algorithm question

#include <iostream>
using namespace std;

int main()
{
  int n[3]={1,2,3};
  for (int i=0; i<3; i++)
  {
    for (int j=1; (j+i) < 3; j++)
    {
      cout << n[i] << n[j+i] << endl;
      cout << n[j+i] << n[i] << endl;
    }
  }
}