A warning is useful only if it arrives while a choice remains. Use the patrol program from the previous lesson; there are no new BASIC lines in this lesson.
Complete source to use
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): DIM c(8)
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
230 RESTORE 9800: FOR i=1 TO 8: READ c(i): NEXT i
240 LET t(6)=1: LET t(10)=1: LET t(12)=1
250 LET rm=1: LET pit=7: LET ci=3: LET cr=c(ci): 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
420 IF dest=cr THEN LET rm=dest: LET ending=2: GO TO 5000
430 LET rm=dest
440 IF t(rm)=1 THEN LET t(rm)=0: LET found=found+1: LET h$="You recover a lost treasure."
460 LET ci=ci+1: IF ci=9 THEN LET ci=1
470 LET cr=c(ci)
480 IF cr=rm THEN LET h$="It arrives! Leave next turn!"
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"
1130 IF v=cr THEN PRINT AT y,15; INK 6;"Footsteps"
1140 IF t(v)=1 THEN PRINT AT y,15; INK 4;"Glint"
1150 IF v=cr AND t(v)=1 THEN PRINT AT y,15; INK 6;"Steps + glint"
1160 NEXT j
1170 IF cr=rm THEN PRINT AT 16,2; INK 6;"IT IS HERE. MOVE NOW."
1180 IF cr<>rm THEN PRINT AT 16,2; INK 7;"No creature in this room."
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$="The cold tunnel hid a pit."
5010 IF ending=2 THEN LET h$="The creature catches you."
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.",8,0,0,11
9800 DATA 2,3,4,8,12,11,10,6Start with R and follow this trace. The creature column shows its position after the action has finished.
| Action | Your room | Creature’s room | What to notice |
|---|---|---|---|
| Start | Entrance, 1 | High ledge, 4 | The opening neighbours are safe |
| S | Root chamber, 5 | Dripping stair, 8 | The patrol advances independently |
| S | Still pool, 9 | Crystal hollow, 12 | You can take time to read |
| E | Buried shrine, 10 | Low arch, 11 | Collect treasure; footsteps are east |
| Space | Buried shrine, 10 | Buried shrine, 10 | It arrives; you still have a choice |
| W | Still pool, 9 | Old camp, 6 | You leave before the next patrol step |
The order is the rule
The program validates a key, works out dest and rejects a wall. Then it counts the action and checks entry into a pit or the creature’s current room. A surviving player moves and collects. Only then does the creature advance and the screen show the new state.
If we ended the game immediately after the creature entered the player’s room, the preceding display could not always warn about that outcome. Here the arrival changes the next decision. The player’s next accepted destination must leave the occupied room.
Invalid keys and blocked exits return before the turn count and creature update. Even during an encounter, a mistyped key or wall does not silently consume the escape opportunity. There is also no real-time deadline: MOVE NOW means “make your next valid action an escape”, not “type quickly”.
At the arrival in room 10, what happens if you press A, then S, then Space?
Show the explanation
A is not a command. S has no tunnel from room 10. Neither advances the turn. Space is a valid wait, so it keeps the destination in the occupied room and the creature catches you.
Try going north from that arrival instead of west. You leave room 10, but the creature’s next patrol room is 6, where you have just gone. It arrives again and gives another escape turn. Leaving an encounter and ending the turn away from the creature are different outcomes.
The twelve-room map and patrol offer an exit at every reachable arrival. That is a property of this authored combination; adding rooms or changing the route means checking it again. A generous rule cannot rescue a map that gives the player nowhere to go.
Run it here
This unit's program, built for you.
- Program
- caverns.tap
- Machine
- ZX Spectrum 48K (PAL)