We can find the target, but the program still asks for more probes afterwards. Now give the discovery an ending and let the player choose whether to search again.
Add lines 15, 300, 5000, 5010, 5020, 5030, 5040, 5050, 5060, 5070, 5080, 5090, 5100, 5110, 5120, 6000, 6010, 6020, 6030, 6040, 6050.
15 GO SUB 5000
300 IF d=0 THEN GO TO 6000
5000 BORDER 1: PAPER 0: INK 7: CLS
5010 PRINT AT 2,9;"SONAR - BANDS"
5020 PRINT AT 5,1;"Find one object on an 8x8 grid."
5030 PRINT AT 7,1;"Enter a row, then a column."
5040 PRINT AT 9,1;"N = near 1-2. M = medium 3-4."
5050 PRINT AT 11,1;"F = far 5+. Rows plus columns."
5060 PRINT AT 13,1;"Old clues stay. > marks latest."
5070 PRINT AT 15,1;"* means found. No probe limit."
5080 PRINT AT 18,1;"Q leaves from any prompt."
5090 INPUT "ENTER to search, Q quits: "; LINE a$
5100 IF a$="q" OR a$="Q" THEN GO TO 9000
5110 IF a$<>"" THEN GO TO 5000
5120 RETURN
6000 INPUT "R another round, Q quits: "; LINE a$
6010 IF LEN a$>16 THEN GO SUB 1000
6020 IF a$="q" OR a$="Q" THEN GO TO 9000
6030 IF a$="r" OR a$="R" THEN GO TO 20
6040 LET s$="Enter R for another round or Q.": GO SUB 2600
6050 GO TO 6000Complete program for this step
10 LET stage=6
15 GO SUB 5000
20 LET tr=3: LET tc=6
25 DIM g(8,8)
26 FOR r=1 TO 8: FOR c=1 TO 8: LET g(r,c)=-1: NEXT c: NEXT r
27 LET n=0: LET lr=0: LET lc=0: LET pr=0: LET pc=0
28 LET d=0: LET v=0: LET a$="": LET b$="": LET p$=""
30 GO SUB 1000
80 LET s$="N=1-2, M=3-4, F=5+ steps.": GO SUB 2600
100 LET p$="Row": GO SUB 3000: LET pr=v
110 LET p$="Column": GO SUB 3000: LET pc=v
120 LET seen=g(pr,pc)
130 LET d=seen
140 IF seen<>-1 THEN GO TO 200
150 LET d=ABS (pr-tr)+ABS (pc-tc)
151 IF d>4 THEN LET d=3: GO TO 160
152 IF d>2 THEN LET d=2: GO TO 160
153 IF d>0 THEN LET d=1
160 LET g(pr,pc)=d: LET n=n+1
200 LET oldr=lr: LET oldc=lc: LET lr=pr: LET lc=pc
210 IF oldr=0 THEN GO TO 240
220 LET r=oldr: LET c=oldc: GO SUB 2100
240 LET r=pr: LET c=pc: GO SUB 2100
250 GO SUB 2500
260 LET s$="Far: at least 5 steps away."
261 IF d=2 THEN LET s$="Medium: 3 or 4 steps away."
262 IF d=1 THEN LET s$="Near: 1 or 2 steps away."
270 IF seen<>-1 THEN LET s$="Already probed. No extra count."
280 IF d=0 THEN LET s$="Found in "+STR$ n+" distinct probes."
290 GO SUB 2600
300 IF d=0 THEN GO TO 6000
310 GO TO 100
1000 BORDER 1: PAPER 0: INK 7: CLS
1010 PRINT AT 0,6;"SONAR N1-2 M3-4 F5+"
1020 FOR c=1 TO 8
1030 PRINT AT 2,6 +3 *(c-1);c
1040 NEXT c
1050 PRINT AT 3,4;"+------------------------+"
1060 PRINT AT 20,4;"+------------------------+"
1070 FOR r=1 TO 8
1080 PRINT AT 4 +2 *(r-1),2;r
1090 FOR k=0 TO 1
1100 PRINT AT 4 +2 *(r-1)+k,4;":";AT 4 +2 *(r-1)+k,29;":"
1110 NEXT k
1120 FOR c=1 TO 8
1130 GO SUB 2100
1150 NEXT c
1160 PAPER 0: INK 7
1170 NEXT r
1180 GO SUB 2500
1190 RETURN
2000 LET y=4 +2 *(r-1): LET x=5 +3 *(c-1)
2010 PAPER 1: INK 7
2020 IF r+c=2 *INT ((r+c)/2) THEN PAPER 5: INK 0
2030 RETURN
2100 GO SUB 2000
2110 LET z=g(r,c): LET b$=". "
2120 IF z=-1 THEN GO TO 2160
2130 LET b$=" F"
2140 IF z=2 THEN LET b$=" M"
2145 IF z=1 THEN LET b$=" N"
2150 IF z=0 THEN LET b$=" *"
2160 LET m$=" "
2170 IF r=lr AND c=lc THEN LET m$=">"
2180 PRINT AT y,x;m$;b$;AT y+1,x;" "
2190 RETURN
2500 PAPER 0: INK 7
2510 PRINT AT 1,0;"Distinct probes: ";n;" "
2520 RETURN
2600 PAPER 0: INK 7
2610 PRINT AT 21,0;" ";
2620 PRINT AT 21,0;s$;
2630 RETURN
3000 PAPER 0: INK 7
3010 INPUT (p$+" (1-8, Q): "); LINE a$
3015 IF LEN a$>16 THEN GO SUB 1000
3020 IF a$="q" OR a$="Q" THEN GO TO 9000
3030 IF LEN a$<>1 THEN GO TO 3100
3040 IF a$<"1" OR a$>"8" THEN GO TO 3100
3050 LET v=VAL a$
3060 RETURN
3100 LET s$="Use one digit from 1 to 8.": GO SUB 2600
3110 GO TO 3010
5000 BORDER 1: PAPER 0: INK 7: CLS
5010 PRINT AT 2,9;"SONAR - BANDS"
5020 PRINT AT 5,1;"Find one object on an 8x8 grid."
5030 PRINT AT 7,1;"Enter a row, then a column."
5040 PRINT AT 9,1;"N = near 1-2. M = medium 3-4."
5050 PRINT AT 11,1;"F = far 5+. Rows plus columns."
5060 PRINT AT 13,1;"Old clues stay. > marks latest."
5070 PRINT AT 15,1;"* means found. No probe limit."
5080 PRINT AT 18,1;"Q leaves from any prompt."
5090 INPUT "ENTER to search, Q quits: "; LINE a$
5100 IF a$="q" OR a$="Q" THEN GO TO 9000
5110 IF a$<>"" THEN GO TO 5000
5120 RETURN
6000 INPUT "R another round, Q quits: "; LINE a$
6010 IF LEN a$>16 THEN GO SUB 1000
6020 IF a$="q" OR a$="Q" THEN GO TO 9000
6030 IF a$="r" OR a$="R" THEN GO TO 20
6040 LET s$="Enter R for another round or Q.": GO SUB 2600
6050 GO TO 6000
9000 LET s$="Finished. RUN to try again.": GO SUB 2600
9010 STOPBegin and end deliberately
The call at line 15 displays the instructions. The routine at 5000 prints the rules and reads an answer: Enter starts, Q leaves, and other answers show the instructions again. Returning from that routine continues with the round setup at line 20.
After each probe, line 300 checks for code zero and transfers to the replay prompt at 6000. The board and discovery message remain visible. R begins another round; Q leaves; other answers produce a reminder without destroying the result. Uppercase and lowercase letters both work.
GO TO 20 restarts the round directly. It is not a subroutine call that needs a later RETURN. Every replay follows the same setup path, so there is no growing chain of unfinished calls.
Reset the state, not just the picture
At line 20, the target is still the fixed (3,6). DIM replaces the old array, and the nested loops fill the new one with -1. The next lines clear the count, old marker, selected coordinates, clue value and temporary strings. Only then is the new board drawn.
Clearing the screen alone would leave the clues in the array. A later redraw could bring the old search back. Resetting the data first gives drawing a genuinely empty search to show.
Why keep the target fixed while checking retry?
Show the explanation
We can reproduce the same probes and expected clues. If an old marker or count survives, we can identify a reset fault without wondering whether a newly chosen target caused the difference.
Run the program from its instructions. Find the target, enter an invalid replay answer, then enter R. Check that all cells are unknown, the count is zero and there is no latest marker. Repeat this several times. Test Q from the instructions, the row prompt, the column prompt and the result screen.
This is already a complete small game: instructions, play, discovery, retry and exit. It is intentionally silent. The symbols and messages carry the feedback, so there is no sound setting needed to understand what happened.
Sources
Steven Vickers, edited by Robin Bradbeer, ZX Spectrum BASIC Programming, second edition (Sinclair Research, 1983), chapters 3, 5 and 12 (control flow, routines and array initialisation).
Run it here
This unit's program, built for you.
- Program
- step-01.tap
- Machine
- ZX Spectrum 48K (PAL)