Strategy
Replace the random fallback with positional sense — take the centre, then a corner, then an edge — and the computer plays well enough to force draws.
The opponent wins and blocks, but when neither applies it still flails at a random square — and a random opening move is how you beat it. The fix is positional sense: when there is no win to take and no threat to stop, prefer the squares that matter. With that, the computer plays a sound game, and most games end in a draw.
10 BORDER 0: PAPER 0: INK 7: CLS
80 RANDOMIZE
90 DIM b(9)
100 LET moves = 0
120 CLS
130 INVERSE 1: PRINT AT 0, 0; " *** THREE IN A ROW *** ": INVERSE 0
150 INK 7: FOR i = 0 TO 3: PLOT 80 + i * 32, 55: DRAW 0, 96: NEXT i
160 FOR i = 0 TO 3: PLOT 80, 55 + i * 32: DRAW 96, 0: NEXT i
170 FOR n = 1 TO 9
180 LET row = INT ((n - 1) / 3)
190 LET col = n - 1 - row * 3
200 LET cx = 100 + col * 32: LET cy = 131 - row * 32
210 IF b(n) = 0 THEN PRINT AT 5 + row * 4, 12 + col * 4; CHR$ (48 + n)
220 IF b(n) = 1 THEN INK 5: PLOT cx - 8, cy - 8: DRAW 16, 16: PLOT cx - 8, cy + 8: DRAW 16, -16: INK 7
230 IF b(n) = 2 THEN INK 2: CIRCLE cx, cy, 8: INK 7
240 NEXT n
250 INPUT "Your move (1-9): "; m
260 IF m < 1 OR m > 9 THEN GO TO 250
270 IF b(m) <> 0 THEN PRINT AT 18, 4; "Already taken!": PAUSE 30: GO TO 120
280 LET b(m) = 1
290 LET moves = moves + 1
300 GO SUB 420
310 IF winner = 1 THEN PRINT AT 18, 4; "You win!": STOP
330 IF moves = 9 THEN PRINT AT 18, 4; "Draw!": STOP
340 GO SUB 600
350 LET b(mv) = 2
360 LET moves = moves + 1
370 BEEP 0.05, 5
380 GO SUB 420
390 IF winner = 2 THEN PRINT AT 18, 4; "Computer wins!": STOP
410 GO TO 120
420 REM --- Check winner ---
430 RESTORE 1200
440 LET winner = 0
450 FOR w = 1 TO 8
460 READ p, q, f
470 IF b(p) <> 0 AND b(p) = b(q) AND b(q) = b(f) THEN LET winner = b(p)
480 NEXT w
490 RETURN
600 REM --- Computer: win, block, strategy ---
610 LET mv = 0
620 RESTORE 1200
630 FOR w = 1 TO 8
640 READ p, q, f
650 IF mv = 0 AND b(p) = 2 AND b(q) = 2 AND b(f) = 0 THEN LET mv = f
660 IF mv = 0 AND b(p) = 2 AND b(f) = 2 AND b(q) = 0 THEN LET mv = q
670 IF mv = 0 AND b(q) = 2 AND b(f) = 2 AND b(p) = 0 THEN LET mv = p
680 NEXT w
690 IF mv > 0 THEN GO TO 850
700 RESTORE 1200
710 FOR w = 1 TO 8
720 READ p, q, f
730 IF mv = 0 AND b(p) = 1 AND b(q) = 1 AND b(f) = 0 THEN LET mv = f
740 IF mv = 0 AND b(p) = 1 AND b(f) = 1 AND b(q) = 0 THEN LET mv = q
750 IF mv = 0 AND b(q) = 1 AND b(f) = 1 AND b(p) = 0 THEN LET mv = p
760 NEXT w
770 IF mv > 0 THEN GO TO 850
780 IF b(5) = 0 THEN LET mv = 5: GO TO 850
790 IF b(1) = 0 THEN LET mv = 1: GO TO 850
800 IF b(3) = 0 THEN LET mv = 3: GO TO 850
810 IF b(7) = 0 THEN LET mv = 7: GO TO 850
820 IF b(9) = 0 THEN LET mv = 9: GO TO 850
830 FOR i = 1 TO 9: IF b(i) = 0 THEN LET mv = i
840 NEXT i
850 RETURN
1200 DATA 1,2,3, 4,5,6, 7,8,9
1210 DATA 1,4,7, 2,5,8, 3,6,9
1220 DATA 1,5,9, 3,5,7
Best square first
The win and block scans are unchanged; only the fallback changes. Lines 780–820 replace the random
pick with a priority list: take the centre (b(5)) if it is free, then a corner (1, 3, 7,
9), and only then settle for whatever is left (lines 830–840). Each line jumps out the moment it
finds a free square, so the order is the strategy — centre controls the most lines, corners the
next most, edges the fewest. Positional judgement that a strong player applies by instinct becomes
five ordered IFs.
Why the game now draws
Noughts and Crosses is a solved game: when both sides play soundly, neither can win. Your opponent now plays soundly — it never misses a win, never lets one through, and opens on strong squares — so a careful player can hold it to a draw but not beat it (line 330 declares the draw once all nine moves are spent with no winner). Reaching that point is the lesson: a short ladder of rules, with no lookahead at all, is enough to play a small game correctly.
The game is complete and fair. The last unit frames it: a title, proper win/lose/draw screens, a running score, and a play-again loop.