TicTacToe function 
1. The method 

!Tic tac toe program
!
!This program reads two idexes i and j of an element of  a matrix 3x3 (board(3,3))
!and assign for the related element the character  "X" or "O".
!
!The program calls first  the subroutine initialize(board) to initialize the elements
!of the matrix by dots. Then reads indexes (1 2 or3 only) from the file "moves.txt ".
!To assigne "X" or  "O" to the element of a matrix, a counter  is incremented to fix
!the first turn for "X" by using the LOGICAL function player(counter).
!If the three elements of a line or of a column or
!of the two diagonals are equal, then the element "X" or "O" WINS.
!
!Finally, the results are written in the output file results.txt. via the 
!subroutine resultboard(board)
!

! --------------------------------------------------

2. Example in Fortran 90 language:
	
!1. Main program:
!-----------------


PROGRAM tictactoe
IMPLICIT NONE
INTEGER:: x, y, iostatus,counter
Character:: board(3,3)
logicaL:: player

! Opening the file: moves.txt
OPEN(UNIT=16,FILE="moves.txt")
counter=1
! Initialize the matrix
CAll initialize(board)
DO
! reading indexes from the file: moves.txt
	READ(16,*,iostat=iostatus) x,y
!Exit at the end
	IF(iostatus /=0) EXIT
!Just three integers
	IF ((x<1) .OR. (x>3) .OR. (y<1) .OR. (y>3)) THEN
		write(*,*) "The board contains 3 rows and 3 columns only, please check your file input"
		stop
	ELSE
		if (board(x,y) == ".") THEN
		! In the case of the LOGICAL function player  returns TRUE
			IF(player(counter)) THEn
				board(x,y) = "X"
			ELSE
				board(x,y) = "O"
			END IF
		ELSE
			write(*,*) "The position"," (",x,",",y,") ","is occupied"
			stop
		END IF
	END IF
!Infrement the counter
	counter = counter + 1
!If the three elements of a line or of a column or
!of the two diagonals are equal, then the element "X" or "O" WINS.
	IF (board(1,1)==board(1,2) .AND. board(1,2)==board(1,3) .AND. board(1,1) /= "." 
	.AND. board(1,2) /= "." .AND. board(1,3) /= ".") THEN
			write(*,*) board(1,1), " wins"
			call resultboard(board)
			stop
		elseif(board(2,1)==board(2,2) .AND. board(2,2)==board(2,3) .AND. board(2,1) /= "." 
		.AND. board(2,2) /= "." .AND. board(2,3) /= ".") THEN
			write(*,*) board(2,1), " wins"
			call resultboard(board)
			stop
		elseif(board(3,1)==board(3,2) .AND. board(3,2)==board(3,3) .AND. board(3,1) /= "." 
		.AND. board(3,2) /= "." .AND. board(3,3) /= ".") THEN
			write(*,*) board(3,1), " wins"
			call resultboard(board)
			stop
		elseif(board(1,1)==board(2,1) .AND. board(2,1)==board(3,1) .AND. board(1,1) /= "." 
		.AND. board(2,1) /= "." .AND. board(3,1) /= ".") THEN
			write(*,*) board(1,1), " wins"
			call resultboard(board)
			stop
		elseif(board(1,2)==board(2,2) .AND. board(2,2)==board(3,2) .AND. board(1,2) /= "." 
		.AND. board(2,2) /= "." .AND. board(3,2) /= ".") THEN
			write(*,*) board(1,2), " wins"
			call resultboard(board)
			stop
		elseif(board(1,3)==board(2,3) .AND. board(2,3)==board(3,3) .AND. board(1,3) /= "." 
		.AND. board(2,3) /= "." .AND. board(3,3) /= ".") THEN
			write(*,*) board(1,3), " wins"
			call resultboard(board)
			stop
		elseif(board(1,1)==board(2,2) .AND. board(2,2)==board(3,3) .AND. board(1,1) /= "." 
		.AND. board(2,2) /= "." .AND. board(3,3) /= ".") THEN
			write(*,*) board(1,1), " wins"
			call resultboard(board)
			stop
		elseif(board(3,1)==board(2,2) .AND. board(2,2)==board(1,3) .AND. board(3,1) /= "." 
		.AND. board(2,2) /= "." .AND. board(1,3) /= ".") THEN
			write(*,*) board(3,1), " wins"
			call resultboard(board)
			stop
	end if

END DO
!If just an element of the matrix is steel a dot, the game is still not completed
	IF(board(1,1)=="." .OR. board(1,2)=="." .OR. board(1,3)=="." .OR. board(2,1)=="."
	.OR. board(2,2)=="."  .OR. board(2,3)=="." .OR. board(3,1)=="." .OR. board(3,2)=="." 
	.OR. board(3,3)==".") then
		write(*,*) "Incomplete Game"
		call resultboard(board)
	else
		write(*,*) "Draw"
		! Put the results in the file ""results.txt
		call resultboard(board)
	end if

CLOSE(16)
END PROGRAM tictactoe




!2. The subroutine to initialize the matrix borard(3,3)
!-------------------------------------------------------
subroutine initialize(a)
IMPLICIT NONE
INTEGER:: i, j
Character:: a(3,3)
Do i=1,3
	DO j=1,3
		a(i,j) = "."
	END DO
END DO
END subroutine initialize



!3. The logical function allowing "X" to take the first , third, fifth ... turns
!--------------------------------------------------------------------------------
LOGICAL function player(counter)
IMPLICIT NONE
integer:: counter
		IF(mod(counter,2) /= 0) THEN
			player = .TRUE.
		ELSE
			player = .FALSE.
		END IF
end function player


!4. The subroutine to output the results within  the file results.txt
!--------------------------------------------------------------------
subroutine resultboard(b)
implicit none
integer:: i
character:: b(3,3)
OPEN(UNIT=15,FILE="results.txt")
do i=1,3
		write(15,*) b(i,1), "|", b(i,2), "|", b(i,3)
end do
CLOSE(15)
end subroutine

! -------------------------------------------------- END


!Example:
!
!file moves.txt
!1 1
!1 2
!2 1
!2 3
!3 1
!3 2
!3 3
!
!file results.txt
! X|O|.
! X|.|O
! X|.|.

!The compiler SciTE.exe gives:
!>g77 -x f77 -ffree-form -W -Wall "ttt.f90" -o "ttt.exe"
!>Exit code: 0

!Running the program:

 !C:\Fortran90>tictactoe
 !X wins