Room 7 is the black shaft. Until now you could walk through it safely. Give that room a consequence and make the warning point to the tunnel that leads there.
Replace lines 250.
Add lines 410, 1120, 5000, 5030, 5040, 5060, 5070, 5080, 5090, 5100, 5110, 5120.
250 LET rm=1: LET pit=7: LET found=0: LET turns=0
410 IF dest=pit THEN LET rm=dest: LET ending=1: GO TO 5000
1120 IF v=pit THEN PRINT AT y,15; INK 6;"Cold draught"
5000 IF ending=1 THEN LET h$="The cold tunnel hid a pit."
5030 GO SUB 1000
5040 PRINT AT 16,2; INK 6;" "
5060 IF ending<>3 THEN PRINT AT 16,2; INK 6;"YOUR EXPEDITION ENDS."
5070 PRINT AT 20,2; INK 7;"R: try again Q: quit ": PRINT AT 21,2;" "
5080 GO SUB 9000
5090 LET k$=INKEY$: IF k$="" THEN GO TO 5090
5100 IF k$="q" OR k$="Q" THEN GO TO 8000
5110 IF k$="r" OR k$="R" THEN GO TO 200
5120 GO TO 5090RUN the changed program.
Complete source at this checkpoint
10 BORDER 0: PAPER 0: INK 7: BRIGHT 1: CLS
200 DIM m(12,4): DIM a$(12,24): DIM b$(12,28): DIM t(12)
210 RESTORE 9500
220 FOR i=1 TO 12: READ a$(i),b$(i): FOR j=1 TO 4: READ m(i,j): NEXT j: NEXT i
240 LET t(6)=1: LET t(10)=1: LET t(12)=1
250 LET rm=1: LET pit=7: LET found=0: LET turns=0
260 LET d$="NSEW": LET e$="nsew": LET h$="Find three lost treasures."
270 GO SUB 1000
300 GO SUB 9000
310 LET k$=INKEY$: IF k$="" THEN GO TO 310
320 IF k$="q" OR k$="Q" THEN GO TO 8000
330 IF k$="r" OR k$="R" THEN GO TO 200
340 LET dir=0: FOR j=1 TO 4: IF k$=d$(j) OR k$=e$(j) THEN LET dir=j
350 NEXT j
360 IF dir=0 AND k$<>" " THEN GO TO 300
370 LET dest=rm
380 IF dir>0 THEN LET dest=m(rm,dir)
390 IF dest=0 THEN PRINT AT 18,2; INK 6;"No tunnel in that direction. ": GO TO 300
400 LET turns=turns+1: LET h$="Your footsteps fade away."
410 IF dest=pit THEN LET rm=dest: LET ending=1: GO TO 5000
430 LET rm=dest
440 IF t(rm)=1 THEN LET t(rm)=0: LET found=found+1: LET h$="You recover a lost treasure."
490 GO TO 270
1000 CLS
1010 PRINT AT 0,8; INK 5;"THE CAVERNS"
1020 PRINT AT 2,2; INK 6;"TREASURE ";found;"/3 TURNS ";turns
1030 INK 1: PLOT 16,148: DRAW 223,0
1040 PRINT AT 5,2; INK 5;a$(rm)
1050 PRINT AT 7,2; INK 7;b$(rm)
1060 PRINT AT 9,2; INK 6;"TUNNELS NEARBY SIGNS"
1070 FOR j=1 TO 4
1080 LET v=m(rm,j): LET y=10 +j
1090 PRINT AT y,2; INK 7;d$(j);" --"
1100 IF v=0 THEN GO TO 1160
1110 PRINT AT y,2; INK 7;d$(j);" Open"
1120 IF v=pit THEN PRINT AT y,15; INK 6;"Cold draught"
1140 IF t(v)=1 THEN PRINT AT y,15; INK 4;"Glint"
1160 NEXT j
1190 PRINT AT 18,2; INK 5;h$
1200 PRINT AT 20,2; INK 7;"N S E W / SPACE waits"
1210 PRINT AT 21,2; INK 7;"R: restart Q: quit"
1220 RETURN
5000 IF ending=1 THEN LET h$="The cold tunnel hid a pit."
5030 GO SUB 1000
5040 PRINT AT 16,2; INK 6;" "
5060 IF ending<>3 THEN PRINT AT 16,2; INK 6;"YOUR EXPEDITION ENDS."
5070 PRINT AT 20,2; INK 7;"R: try again Q: quit ": PRINT AT 21,2;" "
5080 GO SUB 9000
5090 LET k$=INKEY$: IF k$="" THEN GO TO 5090
5100 IF k$="q" OR k$="Q" THEN GO TO 8000
5110 IF k$="r" OR k$="R" THEN GO TO 200
5120 GO TO 5090
8000 PRINT AT 21,2; INK 7;"The Caverns finished. ": STOP
9000 IF INKEY$<>"" THEN GO TO 9000
9010 RETURN
9500 DATA "The entrance","Daylight rims the stone.",0,5,2,0
9510 DATA "Split passage","Two worn paths meet here.",0,6,3,1
9520 DATA "Echo gallery","Every step returns twice.",0,7,4,2
9530 DATA "High ledge","A narrow shelf bends south.",0,8,0,3
9540 DATA "Root chamber","Roots grip the damp ceiling.",1,9,6,0
9550 DATA "Old camp","A torn pack lies in dust.",2,10,7,5
9560 DATA "The black shaft","The floor vanishes below.",3,11,8,6
9570 DATA "Dripping stair","Water counts the seconds.",4,12,0,7
9580 DATA "Still pool","Your lamp trembles in water.",5,0,10,0
9590 DATA "Buried shrine","Carved faces watch the path.",6,0,11,9
9600 DATA "Low arch","You stoop beneath the rock.",7,0,12,10
9610 DATA "Crystal hollow","Crystals catch the lamplight.",8,0,0,11Restart and press S, E. At the Old camp, the east exit should say Cold draught. Press E again: the expedition ends in the shaft. The room and result remain visible; R starts afresh and Q quits.
Check before collecting
pit holds the dangerous room number. Line 410 compares it with dest after the action has been validated and counted, but before the normal move and collection statements. If they match, record the destination in rm, select ending 1 and jump to the result routine.
Recording rm lets the final screen show where the expedition ended. Jumping past collection prevents later parts of the turn from running after a fatal move. The result routine redraws the room, replaces the status and controls, then waits for R or Q.
The pit is a stored rule, not a property of the room’s wording or screen colour. Renaming the black shaft would not make it safe. Changing pit would change which destination is dangerous, so the clue also compares v with pit.
A warning and its consequence must agree
The tunnel table says Cold draught beside the relevant direction. This warning is specific enough to act on: a different open tunnel avoids the pit. The cave is fixed, so the same room remains dangerous on every visit.
The final input loop returns to line 5090 for ignored keys. It does not resume movement or repeatedly apply the ending. R starts at line 200, rebuilding the room data and restoring the treasure flags.
Why does line 410 appear before copying dest into rm on line 430?
Show the explanation
It gives the fatal case its own route. That route records the room and ends immediately. The ordinary route continues to move and collect. What matters is keeping the later turn work from running after the ending; both paths deliberately record the destination.
Try a blocked exit before approaching the pit. It should still cost no turn. Try a number key after falling: the final turn count must stay fixed. The new rule changes legal movement into one room; it does not change input validation.
Sources
Steven Vickers, edited by Robin Bradbeer, ZX Spectrum BASIC Programming, second edition (Sinclair Research, 1983), chapter 5, chapter 13.
Run it here
This unit's program, built for you.
- Program
- caverns.tap
- Machine
- ZX Spectrum 48K (PAL)