Checking for winner in TicTacToe?

Question

What would be the best way to see (in a 2 player) game of Tic Tac Toe who won? Right now I'm using something similar to the following:

if (btnOne.Text == "X" && btnTwo.Text == "X" && btnThree.Text == "X")
{
    MessageBox.Show("X has won!", "X won!");
    return;
}
else
// I'm not going to write the rest but it's really just a bunch
// if statements.

So how do I get rid of the multiple if's?

Answer 1

Something alongs:

rowSum == 3 || columnSum == 3 || diagnolSum == 3

.. ?

Answer 2

Another simple way out would be to save the winnable positions as a data in an array and use a loop to check all possible winning conditions instead of multiple ifs statements

// winnable positions
var winnables = new[] {
    "012",
    "345",
    "678",
    "036",
    "147",
    "258",
    "048",
    "246"
};

// extracted from btnOne Two Three....
var gameState = new[] { "X", "O", "X", "whatever" };


string winner = null;

// check each winnable positions
foreach (var position in winnables) {

    var pos1 = int.Parse(position[0].ToString());
    var pos2 = int.Parse(position[1].ToString());
    var pos3 = int.Parse(position[2].ToString());

    if (gameState[pos1] == gameState[pos2] &&
        gameState[pos2] == gameState[pos3])
        winner = gameState[pos1];

}

// do we have a winner?
if (!string.IsNullOrEmpty(winner))
    /* we've got a winner */

Basically, don't use btnOne btnTwo btnThree, use a proper array of Buttons or an array that saves the game state in a more accessible format and it'll be easier to compute.

Answer 3

If you store your buttons in a multidimenstional array, you can write some extension methods to get the rows, columns and diagonals.

public static class MultiDimensionalArrayExtensions
{
  public static IEnumerable<T> Row<T>(this T[,] array, int row)
  {
    var columnLower = array.GetLowerBound(1);
    var columnUpper = array.GetUpperBound(1);

    for (int i = columnLower; i <= columnUpper; i++)
    {
      yield return array[row, i];
    }
  }

  public static IEnumerable<T> Column<T>(this T[,] array, int column)
  {
    var rowLower = array.GetLowerBound(0);
    var rowUpper = array.GetUpperBound(0);

    for (int i = rowLower; i <= rowUpper; i++)
    {
      yield return array[i, column];
    }
  }

  public static IEnumerable<T> Diagonal<T>(this T[,] array,
                                           DiagonalDirection direction)
  {
    var rowLower = array.GetLowerBound(0);
    var rowUpper = array.GetUpperBound(0);
    var columnLower = array.GetLowerBound(1);
    var columnUpper = array.GetUpperBound(1);

    for (int row = rowLower, column = columnLower;
         row <= rowUpper && column <= columnUpper;
         row++, column++)
   {
      int realColumn = column;
      if (direction == DiagonalDirection.DownLeft)
        realColumn = columnUpper - columnLower - column;

      yield return array[row, realColumn];
    }
  }

  public enum DiagonalDirection
  {
    DownRight,
    DownLeft
  }
}

And if you use a TableLayoutPanel with 3 rows and 3 columns, you can easily create your buttons programmably and store it into a Button[3, 3] array.

Button[,] gameButtons = new Button[3, 3];

for (int row = 0; column <= 3; row++)
  for (int column = 0; column <= 3; column++)
  {
    Button button = new Button();
    // button...
    gameLayoutPanel.Items.Add(button);
    gameButtons[row, column] = button;
  }

And to check for a winner:

string player = "X";
Func<Button, bool> playerWin = b => b.Value == player;
gameButtons.Row(0).All(playerWin) ||
// ...
gameButtons.Column(0).All(playerWin) ||
// ...
gameButtons.Diagonal(DiagonalDirection.DownRight).All(playerWin) ||
// ...