TicTacToe.cs


#define CSHARP2PLUS

namespace AddisonWesley.Michaelis.EssentialCSharp.Chapter04.TicTacToe;

using System;

#pragma warning disable 1030 // Disable user-defined warnings

// The TicTacToe class enables two players to 
// play tic-tac-toe.
public class TicTacToeGame      // Declares the TicTacToeGame class.
{
    static public void Main()  // Declares the entry point to the program.
    {
        // Stores locations each player has moved.
        int[] playerPositions = { 0, 0 };

        // Initially set the currentPlayer to Player 1.
        int currentPlayer = 1;

        // Winning player
        int winner = 0;

        string input = "Let the game begin!";

        // Display the board and 
        // prompt the current player
        // for his next move.
        for(int turn = 1; turn <= 10; ++turn)
        {
            DisplayBoard(playerPositions);

            #region Check for End Game
            if(EndGame(winner, turn, input))
            {
                break;
            }
            #endregion Check for End Game

            input = NextMove(playerPositions, currentPlayer);

            winner = DetermineWinner(playerPositions);

            // Switch players.
            currentPlayer = (currentPlayer == 2) ? 1 : 2;
        }
    }

    private static string NextMove(int[] playerPositions,
                   int currentPlayer)
    {
        string? input;

        // Repeatedly prompt the player for a move
        // until a valid move is entered.
        bool validMove;
        do
        {
            // Request a move from the current player.
            System.Console.Write($"\nPlayer {currentPlayer} - Enter move:");
            // TODO: Update listing in Manuscript
            input = System.Console.ReadLine();
            validMove = ValidateAndMove(playerPositions,
                          currentPlayer, input);
        } while(!validMove);

        return input!;
    }

    static bool EndGame(int winner, int turn, string input)
    {
        bool endGame = false;
        if(winner > 0)
        {
            System.Console.WriteLine($"\nPlayer {winner} has won!!!!");
            endGame = true;
        }
        else if(turn == 10)
        {
            // After completing the 10th display of the
            // board, exit rather than prompting the
            // user again.
            System.Console.WriteLine("\nThe game was a tie!");
            endGame = true;
        }
        else if(input.Length == 0 || input == "quit")
        {
            // Check if user quit by hitting Enter without 
            // any characters or by typing "quit".
            System.Console.WriteLine("The last player quit");
            endGame = true;
        }
        return endGame;
    }

    static int DetermineWinner(int[] playerPositions)
    {
        int winner = 0;

        // Determine if there is a winner.
        int[] winningMasks = {
      7, 56, 448, 73, 146, 292, 84, 273};

        foreach(int mask in winningMasks)
        {
            if((mask & playerPositions[0]) == mask)
            {
                winner = 1;
                break;
            }
            else if((mask & playerPositions[1]) == mask)
            {
                winner = 2;
                break;
            }
        }
        return winner;
    }

    static bool ValidateAndMove(
      int[] playerPositions, int currentPlayer, string? input)
    {
        bool valid = false;

        // Check the current player’s input.
        switch(input)
        {
            case "1":
            case "2":
            case "3":
            case "4":
            case "5":
            case "6":
            case "7":
            case "8":
            case "9":
#warning  "Same move allowed multiple times."
                int shifter;  // The number of places to shift 
                // over to set a bit.
                int position;  // The bit which is to be set.

                // int.Parse() converts "input" to an integer.
                // "int.Parse(input) – 1" because arrays 
                // are zero-based.
                shifter = int.Parse(input) - 1;

                // Shift mask of 00000000000000000000000000000001
                // over by cellLocations.
                position = 1 << shifter;

                // Take the current player cells and OR them 
                // to set the new position as well.
                // Since currentPlayer is either 1 or 2 you 
                // subtract 1 to use currentPlayer as an
                // index in a zero-based array.
                playerPositions[currentPlayer - 1] |= position;

                valid = true;
                break;

            case null:
            case "quit":
                valid = true;
                break;

            case "":
            default:
                // If none of the other case statements
                // is encountered, then the text is invalid.
                System.Console.WriteLine(
                    "\nERROR:  Enter a value from 1-9. "
                    + "Push ENTER to quit");
                break;
        }

        return valid;
    }

    static void DisplayBoard(int[] playerPositions)
    {
        // This represents the borders between each cell
        // for one row.
        string[] borders = {
"|", "|", "\n---+---+---\n", "|", "|",
"\n---+---+---\n", "|", "|", ""
};

        // Display the current board;
        int border = 0;  // set the first border (border[0] = "|").

#if CSHARP2PLUS
        System.Console.Clear();
#endif

        for(int position = 1;
             position <= 256;
             position <<= 1, border++)
        {
            char token = CalculateToken(
                playerPositions, position);

            // Write out a cell value and the border that 
            // comes after it.
            System.Console.Write($" {token} {borders[border]}");
        }
    }

    static char CalculateToken(
        int[] playerPositions, int position)
    {
        // Initialize the players to 'X' and 'O'
        char[] players = { 'X', 'O' };

        char token;
        // If player has the position set, 
        // then set the token to that player.
        if((position & playerPositions[0]) == position)
        {
            // Player 1 has that position marked.
            token = players[0];
        }
        else if((position & playerPositions[1]) == position)
        {
            // Player 2 has that position marked.
            token = players[1];
        }
        else
        {
            // The position is empty.
            token = ' ';
        }
        return token;
    }

#line 113 "TicTacToe.cs"
    // Generated code goes here.
#line default
}