TicTacToe

// https://en.wikipedia.org/wiki/Tic-tac-toe and http://www.se16.info/hgb/tictactoe.htm
// If played properly, tic-tac-toe will end in a draw, making tic-tac-toe a futile game.
// Total number of X and O placements on a 3x3 grid = 9! = 362880, but many games end before completely filling in the grid.
// Also, many tic-tac-toe outcomes are logically equivalent in terms of reflection and rotation symmetries.

using System;

namespace TicTacToe
{
    class Program
    {
        static void Main()
        {
            while (true) // each iteration of this outer loop is a new game
            {
                int i = 1;           // center cell position in 0, 1, 2 columns
                int j = 1;           // center cell position in 0, 1, 2 rows
                bool xIsNext = true; // true if next move is X, false if next move is O
                string outcome = ""; // gets the string "X" if X wins, "O" if O wins, or "" for a draw
                string[,] board = { { "", "", "" }, { "", "", "" }, { "", "", "" } };
                int moveCount = 0;   // can never be more than 9 moves where each X or O placement is a single move
                Console.Clear();
                WriteAt(0, 0, "   |   |   ");
                WriteAt(0, 1, "---+---+---");
                WriteAt(0, 2, "   |   |   ");
                WriteAt(0, 3, "---+---+---");
                WriteAt(0, 4, "   |   |   ");
                Console.SetCursorPosition(10, 10);
                Console.WriteLine("Use arrow keys to move from cell to cell and hit enter to place a token.");

                Console.CursorLeft = 1;
                Console.CursorTop = 0;
                Console.SetCursorPosition(1 + (4 * i), 2 * j); // offsets and multiliers to position in cell centers

                while (true) // each iteration of this inner loop is the placement of an "X" or a "Y as a single move
                {
                    ConsoleKeyInfo consoleKeyInfo = Console.ReadKey(true); // get a key stroke without echo to output
                    switch (consoleKeyInfo.Key)
                    {
                        case ConsoleKey.RightArrow:
                            i = (i + 1) % 3;
                            Console.SetCursorPosition(1 + (4 * i), 2 * j);
                            break;
                        case ConsoleKey.LeftArrow:
                            i = (i + 2) % 3;
                            Console.SetCursorPosition(1 + (4 * i), 2 * j);
                            break;
                        case ConsoleKey.DownArrow:
                            j = (j + 1) % 3;
                            Console.SetCursorPosition(1 + (4 * i), 2 * j);
                            break;
                        case ConsoleKey.UpArrow:
                            j = (j + 2) % 3;
                            Console.SetCursorPosition(1 + (4 * i), 2 * j);
                            break;
                        case ConsoleKey.Enter:
                            if (board[i, j] != "") { Console.Beep(); break; } // cannot place X or O in cell that is already played
                            string token = xIsNext ? "X" : "O";               // select token to place in cell for this move
                            board[i, j] = token;
                            WriteAt(1 + (4 * i), 2 * j, token);
                            xIsNext = !xIsNext;                               // alternate X/O token for next move
                            moveCount++;                                      // count number of completed moves so far 
                            break;
                    }

                    outcome = WhoWon(board, moveCount);
                    if (outcome != "") break;
                }

                Console.SetCursorPosition(10, 10);
                Console.WriteLine("Game Over. Winner: " + outcome + ". Hit q to quit, or hit any other key to play again.");
                if (Console.ReadKey(true).Key == ConsoleKey.Q) break; else continue;
            }
            Console.Clear();
        }
        protected static void WriteAt(int x, int y, string s)
        {
            try
            {
                Console.SetCursorPosition(x, y);
                Console.Write(s);
            }
            catch (ArgumentOutOfRangeException e)
            {
                Console.Clear();
                Console.WriteLine(e.Message);
            }
        }

        protected static string WhoWon(string[,] board, int moveCount)
        {
            // check to see if X won yet
            if (board[0, 0] == "X" && board[0, 1] == "X" && board[0, 2] == "X" ||
                (board[1, 0] == "X" && board[1, 1] == "X" && board[1, 2] == "X") ||
                (board[2, 0] == "X" && board[2, 1] == "X" && board[2, 2] == "X") ||
                (board[0, 0] == "X" && board[1, 0] == "X" && board[2, 0] == "X") ||
                (board[0, 1] == "X" && board[1, 1] == "X" && board[2, 1] == "X") ||
                (board[0, 2] == "X" && board[1, 2] == "X" && board[2, 2] == "X") ||
                (board[0, 0] == "X" && board[1, 1] == "X" && board[2, 2] == "X") ||
                (board[0, 2] == "X" && board[1, 1] == "X" && board[2, 0] == "X")) return "X";

            // check to see if O won yet
            if (board[0, 0] == "O" && board[0, 1] == "O" && board[0, 2] == "O" ||
                (board[1, 0] == "O" && board[1, 1] == "O" && board[1, 2] == "O") ||
                (board[2, 0] == "O" && board[2, 1] == "O" && board[2, 2] == "O") ||
                (board[0, 0] == "O" && board[1, 0] == "O" && board[2, 0] == "O") ||
                (board[0, 1] == "O" && board[1, 1] == "O" && board[2, 1] == "O") ||
                (board[0, 2] == "O" && board[1, 2] == "O" && board[2, 2] == "O") ||
                (board[0, 0] == "O" && board[1, 1] == "O" && board[2, 2] == "O") ||
                (board[0, 2] == "O" && board[1, 1] == "O" && board[2, 0] == "O")) return "O";

            // max number of completed moves is 9
            if (moveCount == 9) return "Draw";

            return ""; // game still in play (no winner yet, and ;ess than 9 moves have been completed
        }
    }
}