We need to know when the game is over: either by a victory of any of the player or where there’s simply no empty cell where a move can be made.

there’s simply no empty cell where a move can be made.

Finding the Winner

To determine, if a player managed to form a line of 3 cells, we use simply check if the @verification string contains a XXX or OOO substring:

IF 
    IndexOf(@verification,'OOO') > 0
        THEN 
            set @state = "Os Win!"
            set @stateClass = "o"
            set @firstPlayer = 'X'
ELSEIF 
    IndexOf(@verification,'XXX') > 0
        THEN 
            set @state = "Xs Win!"
            set @stateClass = "x"
            set @firstPlayer = 'O'

Drawing Conclusions

To see if a draw occurred, we replace all instances Xs and Os with nothing. If the resulting string is empty, we know that the game can’t continue as there are no cells that weren’t taken by any of the player.

ELSEIF
    Replace(Replace(@fields, "O"), "X") == ""
        THEN 
            set @state = "Draw!"
            set @stateClass = "d"
            set @firstPlayer = IIF(@firstPlayer == "X", "O", "X")

Examples

Player X Wins

For this board our variables would get the following values:

set @fields = "X2OOO6XXX"
/* ... */
set @verification = 'XEO^OOE^XXX^XOX^EOX^OEX^XOX^XOO^'

/* 'XXX' found at position 9 which is bigger than 0 */
IF 
    IndexOf(@verification,'XXX') > 0 
        THEN 
            set @state = "Xs Win!"
            set @stateClass = "x"
            set @firstPlayer = 'O'

A draw occurs

For this board our variables would get the following values:

set @fields = 'XOXXOOOXX'

/* If we replace all X's and O's, the resulting string is empty*/
ELSEIF
    Replace(Replace(@fields, "O"), "X") == ""
        THEN 
            set @state = "Draw!"
            set @stateClass = "d"
            set @firstPlayer = IIF(@firstPlayer == "X", "O", "X")

The game continues

This is neither a draw nor a victory, so the game can continue.

For this board our variables would get the following values:

set @fields = 'X234O678X'
/* ... */
set @verification = 'X23^4O6^78X^X47^2O8^36X^XOX^7O3^'

/* No player has won and there are moves possible */
ELSE
    set @state = Concat("Local Multiplayer:<br>", @playerTurn, "s turn")

Next moves​

As you can see in the last example, new variables have appeared:

• @state will be displayed to the player and show:
  • who won the game
  • that the game concluded in a draw
  • which player’s turn it is
• @stateClass is the name of the CSS class for a box displaying the @state
• @firstPlayer tells us which player started the game

Speaking of CSS classes, let’s build the interface.