Unit 10: Keep the game - Three In A Row - Spectrum

Save the finished program so a fresh Spectrum session can load it and show its title. We are saving the program, not an unfinished match.

Complete source to use

three.bas

  10 BORDER 0: PAPER 0: INK 7: BRIGHT 1: CLS
  20 LET wins=0: LET losses=0: LET draws=0: LET first=1
  30 PRINT AT 3,6; INK 5;"T H R E E  I N  A  R O W"
  40 PRINT AT 7,2;"You are X. The computer is O."
  50 PRINT AT 9,4;"Three in a line wins."
  60 PRINT AT 11,4;"Choose a square with 1-9."
  70 PRINT AT 13,2;"Watch why O chooses its move."
  80 PRINT AT 16,4;"R restarts. Q quits."
  90 PRINT AT 19,6; INK 5;"S starts. Q quits."
 100 GO SUB 9000
 110 LET k$=INKEY$: IF k$="" THEN GO TO 110
 120 IF k$="q" OR k$="Q" THEN GO TO 8000
 130 IF k$<>"s" AND k$<>"S" THEN GO TO 110
 200 DIM b(9): LET moves=0: LET winner=0: LET wl=0: LET a$=""
 210 GO SUB 1000
 220 IF first=2 THEN GO TO 600
 250 GO SUB 9000
 260 LET k$=INKEY$: IF k$="" THEN GO TO 260
 270 IF k$="q" OR k$="Q" THEN GO TO 8000
 280 IF k$="r" OR k$="R" THEN GO TO 200
 290 IF k$<"1" OR k$>"9" THEN GO TO 250
 300 LET n=VAL k$
 310 IF b(n)<>0 THEN PRINT AT 18,2; INK 6;"Taken. Choose an empty square.": GO TO 250
 320 LET b(n)=1: LET moves=moves+1: GO SUB 2000
 330 GO SUB 3000
 340 IF winner>0 OR moves=9 THEN GO TO 5000
 600 PRINT AT 18,2; INK 6;"O is choosing...             "
 610 GO SUB 4000
 620 LET n=mv: LET b(n)=2: LET moves=moves+1: GO SUB 2000
 630 PRINT AT 19,2; INK 5;"O chose ";mv;": ";a$;"        "
 640 GO SUB 3000
 650 IF winner>0 OR moves=9 THEN GO TO 5000
 660 PRINT AT 18,2; INK 7;"Your move: choose 1-9.        "
 670 GO TO 250
1000 CLS
1010 PRINT AT 0,8; INK 5;"THREE IN A ROW"
1020 PRINT AT 1,2; INK 7;"W ";wins;"   L ";losses;"   D ";draws
1030 INK 1: FOR i=0 TO 3: PLOT 56 +i*48,32: DRAW 0,120: NEXT i
1040 FOR i=0 TO 3: PLOT 56,32 +i*40: DRAW 144,0: NEXT i
1050 FOR n=1 TO 9: GO SUB 2000: NEXT n
1060 PRINT AT 18,2; INK 7;"Your move: choose 1-9."
1070 IF first=1 THEN PRINT AT 19,2; INK 5;"You start this round."
1080 IF first=2 THEN PRINT AT 19,2; INK 5;"O starts this round."
1090 PRINT AT 21,2; INK 7;"1-9: place  R: reset  Q: quit"
1100 RETURN
2000 LET row=INT ((n-1)/3): LET col=n-1 -row*3
2010 LET x=80 +col*48: LET y=132 -row*40
2020 PRINT AT 5 +row*5,10 +col*6; INK 7;" "
2030 IF b(n)=0 THEN PRINT AT 5 +row*5,10 +col*6; INK 7;n: RETURN
2040 IF b(n)=2 THEN GO TO 2100
2050 INK 5: FOR z=0 TO 1: PLOT x-10 +z,y-10: DRAW 20,20: PLOT x-10 +z,y+10: DRAW 20,-20: NEXT z
2060 RETURN
2100 INK 7: FOR z=0 TO 1: PLOT x-6,y+10 -z: DRAW 12,0: DRAW 4,-4: DRAW 0,-12: DRAW -4,-4: DRAW -12,0: DRAW -4,4: DRAW 0,12: DRAW 4,4: NEXT z
2110 RETURN
3000 LET winner=0: LET wl=0: RESTORE 9500
3010 FOR w=1 TO 8: READ p,q,f
3020 IF b(p)<>0 AND b(p)=b(q) AND b(q)=b(f) THEN LET winner=b(p): LET wl=w
3030 NEXT w: RETURN
4000 LET mark=2: GO SUB 4500
4010 IF mv>0 THEN LET a$="win": RETURN
4020 LET mark=1: GO SUB 4500
4030 IF mv>0 THEN LET a$="block": RETURN
4040 IF b(5)=0 THEN LET mv=5: LET a$="centre": RETURN
4050 RESTORE 9530
4060 FOR j=1 TO 4: READ v
4070 IF mv=0 AND b(v)=0 THEN LET mv=v
4080 NEXT j
4090 IF mv>0 THEN LET a$="corner": RETURN
4100 FOR j=1 TO 9: IF b(j)=0 THEN LET mv=j
4110 NEXT j: LET a$="edge": RETURN
4500 LET mv=0: RESTORE 9500
4510 FOR w=1 TO 8: READ p,q,f
4520 IF mv=0 AND b(p)=mark AND b(q)=mark AND b(f)=0 THEN LET mv=f
4530 IF mv=0 AND b(p)=mark AND b(f)=mark AND b(q)=0 THEN LET mv=q
4540 IF mv=0 AND b(q)=mark AND b(f)=mark AND b(p)=0 THEN LET mv=p
4550 NEXT w: RETURN
5000 IF winner=1 THEN LET wins=wins+1: LET r$="YOU WIN. Three in a row."
5010 IF winner=2 THEN LET losses=losses+1: LET r$="O WINS. Three in a row."
5020 IF winner=0 THEN LET draws=draws+1: LET r$="DRAW. No line completed."
5030 IF wl>0 THEN GO SUB 6000
5040 PRINT AT 18,2; INK 6;r$;"      "
5050 PRINT AT 1,2; INK 7;"W ";wins;"   L ";losses;"   D ";draws;"  "
5060 PRINT AT 21,2;"R: next round   Q: quit      "
5070 GO SUB 9000
5080 LET k$=INKEY$: IF k$="" THEN GO TO 5080
5090 IF k$="q" OR k$="Q" THEN GO TO 8000
5100 IF k$<>"r" AND k$<>"R" THEN GO TO 5080
5110 LET first=3 -first: GO TO 200
6000 RESTORE 9500: FOR w=1 TO wl: READ p,q,f: NEXT w
6010 LET row=INT ((p-1)/3): LET col=p-1 -row*3
6020 LET sx=80 +col*48: LET sy=132 -row*40
6030 LET row=INT ((f-1)/3): LET col=f-1 -row*3
6040 INK 6: PLOT sx,sy: DRAW 80 +col*48 -sx,132 -row*40 -sy: RETURN
8000 PAPER 0: INK 7: BRIGHT 0: PRINT AT 21,2;"Three in a Row finished.     ": STOP
9000 IF INKEY$<>"" THEN GO TO 9000
9010 RETURN
9500 DATA 1,2,3,4,5,6,7,8,9
9510 DATA 1,4,7,2,5,8,3,6,9
9520 DATA 1,5,9,3,5,7
9530 DATA 1,3,7,9

Quit with Q. Follow the Meet BASIC tape workflow to prepare recording in your emulator. At the BASIC prompt enter SAVE "three" LINE 10. SAVE is a keyword; LINE is entered in extended mode with Symbol Shift and 3. Confirm the recording prompt when the tape recorder or emulator is ready.

"three" is the tape filename. LINE 10 records the line at which execution should begin when loaded. Our line 10 clears the screen and line 20 resets the session, so loading this tape starts with a clean tally and the opening instructions.

Check the saved copy

Use a fresh stock 48K session. Mount the saved tape, enter LOAD "" and start playback. Do not rely on the old program still being in memory. When loading finishes, the title should appear without an extra RUN command.

Press S and place a mark. Read O’s reply and reason.
Complete a round. Leave the result visible and check the tally.
Press R. Check that the other side starts.
Restart before finishing. Check that the starter and tally stay the same.
Press Q. The program should stop cleanly.

If loading leaves you at a prompt instead of the title, check that the saved command included LINE 10. If you cannot find a tape file in the emulator, confirm that its recording was exported or saved to the host; a BASIC SAVE command and a durable host file are separate parts of the workflow.

Why does loading the program not resume your half-played board?

Show the explanation

The tape starts execution at line 10. The session values are reset and line 200 creates a new empty board. This game deliberately starts afresh instead of providing a saved-match feature.

You now have a complete small opponent: it follows rules in a clear order, explains the rule it used and leaves its mistakes open to investigation. Change a preference only after predicting which position it will affect, then replay that position to see whether the change did what you intended.

Sources

Steven Vickers, edited by Robin Bradbeer, ZX Spectrum BASIC Programming, second edition (Sinclair Research, 1983), chapter 20.

Run it here

This unit's program, built for you.

Program: three.tap
Machine: ZX Spectrum 48K (PAL)

Download three.tap