for(int i = 0; i < 9; i=i){
                cout << " " << i++ << " | " << i++ << " | " << i++ << "\n";

                //avoids printing a line at the end of the board
                if(i != 9){
                        cout << "-----------\n";
                }
        }

outputs:


 2 | 1 | 0
-----------
 5 | 4 | 3
-----------
 8 | 7 | 6