5 RANDOMIZE VAL(MID$(TIME$, 7))
10 REM ***** Tic-tac-toe ***** 
20 CLS: SCREEN 1
30 DIM BOARD(3, 3): DIM TILEVALUE(3, 3)
40 DIM ROWS(8, 3, 2): DIM BESTMOVE(9, 2)
50 RESTORE 1000
60 FOR A = 1 TO 8: FOR B = 1 TO 3
70 READ ROWS(A, B, 1), ROWS(A, B, 2)
80 NEXT: NEXT
90 LINE (150, 20)-(150, 80): LINE (170, 20)-(170, 80): LINE (130, 40)-(190, 40): LINE (190, 60)-(130, 60)
100 REM ***** Beginning of game ***** 
110 TURNS = 0
120 VIEW PRINT 16 TO 24: CLS 2: GOTO 5000
200 REM ***** Human moves ***** 
210 VIEW PRINT 16 TO 24: CLS 2
220 LOCATE 16, 1: INPUT "Where do you want to move? (Use letter for column, number for row)"; A$
230 IF LEN(A$) <> 2 THEN PRINT "Invalid coordinates": GOTO 210
240 A1$ = MID$(A$, 1, 1)
250 IF A1$ > "Z" THEN A1$ = CHR$(ASC(A1$) - 32)
260 IF A1$ > "C" OR A1$ < "A" THEN PRINT "Please input a valid column: from A to C.": GOTO 210
270 X = ASC(A1$) + 1 - ASC("A")
280 A2$ = MID$(A$, 2, 1)
290 IF A2$ < "1" OR A2$ > "3" THEN PRINT "Please input a valid row: from 1 to 3.": GOTO 210
300 Y = VAL(A2$)
310 IF BOARD(X, Y) <> 0 THEN PRINT "Tile is already full.": GOTO 210
320 PLAYER = 1: GOSUB 2000
330 BOARD(X, Y) = 1
340 GOSUB 3000
350 TURNS = TURNS + 1: IF TURNS >= 9 THEN GOTO 4010
400 REM ***** Computer moves *****
410 REM ***** Row appraisal *****
420 FOR F=1 TO 3:FOR G=1 TO 3:TILEVALUE(F,G)=0:NEXT :NEXT
430 FOR A=1 TO 8:FULLLINE=0
440 FOR B=1 TO 3
450 FULLLINE=FULLLINE+BOARD(ROWS(A,B,1),ROWS(A,B,2))
460 NEXT
470 FOR B=1 TO 3
480 XL=ROWS(A,B,1):YL=ROWS(A,B,2)
490 IF FULLLINE=1 THEN TILEVALUE(XL,YL)=TILEVALUE(XL,YL)+1
500 IF FULLLINE=-1 THEN TILEVALUE(XL,YL)=TILEVALUE(XL,YL)+5
510 IF FULLLINE=2 THEN TILEVALUE(XL,YL)=TILEVALUE(XL,YL)+21
520 IF FULLLINE=-2 THEN TILEVALUE(XL,YL)=TILEVALUE(XL,YL)+85
530 NEXT
540 NEXT
550 MAXIMUM=0:FOR A=1 TO 3:FOR B=1 TO 3
560 IF BOARD(A,B)<>0 THEN TILEVALUE(A,B)=-1
570 IF TILEVALUE(A,B)>MAXIMUM THEN MAXIMUM=TILEVALUE(A,B)
580 NEXT :NEXT
590 BESTCOUNT=0
600 FOR A=1 TO 3:FOR B=1 TO 3
610 IF TILEVALUE(A,B)=MAXIMUM THEN BESTCOUNT=BESTCOUNT+1:BESTMOVE(BESTCOUNT,1)=A:BESTMOVE(BESTCOUNT,2)=B
620 NEXT :NEXT
630 MYMOVE=INT(RND*BESTCOUNT-1)+1
640 IF MYMOVE=0 THEN PRINT "ERROR: MYMOVE=0":MYMOVE=1
650 IF MYMOVE>9 THEN PRINT "ERROR: MYMOVE>9":MYMOVE=9
660 X=BESTMOVE(MYMOVE,1)
670 Y=BESTMOVE(MYMOVE,2)
680 IF MAXIMUM<=4 AND BOARD(2,2)=0 THEN X=2:Y=2
690 PRINT "My move:";CHR$(ASC("A")+X-1);Y
700 IF BOARD(X,Y)<>0 THEN PRINT "Tile already full":GOTO 630
710 PLAYER =2 :GOSUB 2000
720 BOARD(X,Y)=-1
730 GOSUB 3000
740 TURNS=TURNS+1:IF TURNS>=9 THEN GOTO 4010
750 GOTO 210
1000 REM Store data for the 9 possible rows
1010 DATA 1,1,1,2,1,3: REM row 1 
1020 DATA 2,1,2,2,2,3: REM row 2 
1030 DATA 3,1,3,2,3,3: REM row 3 
1040 DATA 1,1,2,1,3,1: REM column 1 
1050 DATA 1,2,2,2,3,2: REM column 2 
1060 DATA 1,3,2,3,3,3: REM column 3 
1070 DATA 1,1,2,2,3,3: REM diag. 1 
1080 DATA 3,1,2,2,1,3: REM diag. 2 
2000 REM Draw cross or circle
2010 IF PLAYER = 1 THEN GOTO 2040
2020 CIRCLE (120 + 20 * X, 10 + 20 * Y), 10, 1
2030 RETURN
2040 LINE (110 + 20 * X, 20 * Y)-(130 + 20 * X, 20 + 20 * Y), 2
2050 LINE (110 + 20 * X, 20 + 20 * Y)-(130 + 20 * X, 20 * Y), 2
2060 RETURN
3000 REM ***** Three in a row? ***** 
3010 FOR A = 1 TO 8
    3020 FULLLINE = 0: FOR B = 1 TO 3
        3030 FULLLINE = FULLLINE + BOARD(ROWS(A, B, 1), ROWS(A, B, 2))
    3040 NEXT
    3050 IF FULLLINE = 3 THEN PRINT "Tic tac toe! You won!": GOTO 4010
    3060 IF FULLLINE = -3 THEN PRINT "Tic tac toe! I won!": GOTO 4010
3070 NEXT
3080 RETURN
4000 REM ***** Play again? ***** 
4010 INPUT "Do you want to play again?"; A$
4020 IF MID$(A$, 1, 1) = "Y" OR MID$(A$, 1, 1) = "y" THEN RUN
4030 IF MID$(A$, 1, 1) = "N" OR MID$(A$, 1, 1) = "n" THEN END
4040 PRINT "Please input 'Y' for 'yes', 'N' for 'no'": GOTO 4010
5000 REM ***** Decide starting player ***** 
5010 INPUT "1- I start     2- You start"; N
5020 IF N = 1 THEN GOTO 400
5030 IF N = 2 THEN GOTO 200
5040 GOTO 5000