10 REM CAVES.ECB
  100 REM ..***  CAVES1  ***  Source ??? via EAGAN  REH 3-81
  110 REM ..***  PROGRAM MAKES A SET OF LINKED ROOMS
  120 REM ..for you to explore        : Revised 3-10-81  R.E.H.
  130 DIM N(127),P(385),L(99)
  140 DEF FNP(X)=INT(P(X)/512)
  150 DEF FNN(X)=P(X)-INT(P(X)/512)*512
  160 LET G=1,G2=1
  170 PRINT "&K&J&J"
  180 PRINT "WELCOME TO THE CAVES"
  190 PRINT : PRINT : PRINT
  200 PRINT "IS THIS YOUR FIRST VISIT (Y=YES, N=NO) ---=>";
  210 INPUT (1,0)X$: LET X$=X$+"Y"
  220 LET X$=X$(1,1)
  230 IF X$(1,1)="Y" THEN 290
  235 IF X$(1,1)="y" THEN 290
  240 PRINT
  250 PRINT "  1 = USUAL,  2 = HARDER,  3 = !!!   ---=>";
  260 INPUT G
  270 LET G=ABS(G)
  280 IF G<4 THEN 290 ELSE  LET G=3
  290 LET V1=0
  300 GOSUB 1850
  310 LET R=2
  320 LET I=1
  325 PRINT "&J+*+ I need a minute to set up the CAVES +*+&J"
  330 GOSUB 1280
  340 GOSUB 1420
  350 LET J=1
  360 GOSUB 1370
  370 GOSUB 1420
  380 LET J=J+1
  390 IF J<=G-1 THEN 360 ELSE  LET I=I+1
  400 IF I<=4 THEN 330 ELSE  LET W=R-1
  410 IF G2>1 THEN 630 ELSE  PRINT
  420 PRINT "DO YOU WANT AN INTRODUCTION (Y=YES, N=NO) ---=>";
  430 INPUT (1,0)X$: LET X$=X$+"N"
  440 LET X$=X$(1,1)
  450 IF X$(1,1)="N" THEN 630 ELSE  PRINT
  460 PRINT
  470 PRINT "   IMAGINE YOURSELF AN EXPLORER OF THE FAMOUS"
  480 PRINT "DUZZLEDORF CAVES.  YOU'VE BEEN UNDERGROUND"
  490 PRINT "FOR DAYS, TRIPPING THROUGH THE CAVERNS AND"
  500 PRINT "TUNNELS.  UNFORTUNATELY, YOU'RE LOST, AND"
  510 PRINT "YOUR FOOD HAS RUN OUT."
  520 PRINT
  530 PRINT "   THERE IS ONLY ONE PATH OUT.  SEE IF YOU"
  540 PRINT "CAN FIND IT."
  550 PRINT
  560 PRINT "GIVE ME THE NUMBER"
  570 PRINT "OF THE CAVERN YOU WANT TO GO TO. LIKE THIS:"
  580 PRINT
  590 PRINT
  600 PRINT "ADVICE: MAKE A MAP AS YOU GO - IN THE HARDER CAVES"
  610 PRINT "        YOU SOMETIMES HAVE TO GO BACK AND TRY ANOTHER"
  620 PRINT "        WAY. GOOD LUCK!"
  630 LET D1=1
  640 LET V1=8
  650 GOSUB 1850
  660 LET X=9999
  670 PRINT
  680 PRINT "YOU'RE IN CAVERN #";N1
  690 LET D1=9999
  700 LET V1=7
  710 LET I=1
  720 GOSUB 1850
  730 PRINT "#";D1;"  ";
  740 IF D1=W THEN 770 ELSE  LET I=I+1
  750 IF I<=3 THEN 720
  760 IF N1=1 THEN 830
  770 LET V1=4
  780 GOSUB 1850
  790 PRINT "#";N1;"  ";
  800 LET X=N1
  810 LET V1=6
  820 GOSUB 1850
  830 PRINT "ARE WHERE YOU CAN GO"
  840 PRINT "WHERE NEXT  ---=>";
  850 INPUT D1
  860 IF D1=N1 THEN 840
  870 IF D1=X THEN  LET V1=4 ELSE 900
  880 GOSUB 1850
  890 GOTO 670
  900 LET V1=6
  910 GOSUB 1850
  920 IF V2>0 THEN 940 ELSE  PRINT "ILLEGAL MOVE"
  930 GOTO 840
  940 IF N1=W THEN 1010 ELSE  LET D1=9999
  950 LET V1=7
  960 GOSUB 1850
  970 IF D1=9999 THEN  PRINT "DEADEND" ELSE 670
  980 LET V1=4
  990 GOSUB 1850
 1000 GOTO 840
 1010 PRINT "&K"
 1020 PRINT
 1030 PRINT TAB(10);"!!!   SUNLIGHT   !!!"
 1040 PRINT
 1050 PRINT TAB(10);"!!!  FRESH  AIR  !!!"
 1060 PRINT
 1070 PRINT TAB(10);"...  REPORTERS   ..."
 1080 PRINT
 1090 PRINT
 1100 PRINT "WELL, AT LEAST YOU'RE OUT"
 1110 IF G>1 THEN 1160 ELSE  PRINT
 1120 PRINT "CONGRATULATIONS, INTREPID EXPLORER"
 1130 PRINT "OF THE FEARSOME CAVES.  IF YOU WANT TO"
 1140 PRINT "EXPLORE AGAIN, YOU CAN CHOOSE A HARDER SET"
 1150 PRINT "OF CAVES OR ANOTHER ONE JUST AS DIFFICULT"
 1160 PRINT
 1170 PRINT "PLAY AGAIN?  (Y=YES, N=NO) ---=>";
 1180 INPUT (1,0)X$: LET X$=X$+"Y"
 1190 LET X$=X$(1,1)
 1195 IF X$(1,1)="n" THEN 1260
 1200 IF X$(1,1)="N" THEN 1260 ELSE  LET G2=G2+1
 1210 IF G=3 THEN 270
 1220 PRINT "HARDER GAME? (Y OR N)  ---=>";
 1230 INPUT X$: LET X$=X$+"Y"
 1240 LET X$=X$(1,1)
 1250 IF X$(1,1)="Y" THEN  LET G=G+1 ELSE  PRINT
 1260 IF X$(1,1)="Y" THEN 270 ELSE  PRINT "BYE"
 1270 GOTO 3790
 1280 REM ..*** ADD DAUGHTERS TO CURRENT NODE
 1290 LET V1=1
 1300 LET J1=1
 1310 IF R=50 THEN 1360 ELSE  LET D1=R
 1320 GOSUB 1850
 1330 LET R=R+1
 1340 LET J1=J1+1
 1350 IF J1<=3 THEN 1310
 1360 RETURN
 1370 REM ..*** CREATE DAUGHTERS, AND RETURN
 1380 GOSUB 1280
 1390 LET V1=4
 1400 GOSUB 1850
 1410 RETURN
 1420 REM ..*** PICK A DAUGHTER NODE AT RANDOM AND GO DOWN
 1430 LET V1=7
 1440 LET J1=1
 1450 LET J2=INT(RND(0)*3)+1
 1460 GOSUB 1850
 1470 IF D1=9999 THEN 1460 ELSE  LET J1=J1+1
 1480 IF J1<=J2 THEN 1460 ELSE  LET V1=6
 1490 GOSUB 1850
 1500 LET D1=9999
 1510 LET V1=7
 1520 GOSUB 1850
 1530 IF D1=9999 THEN 1560 ELSE  LET V1=4
 1540 GOSUB 1850
 1550 GOTO 1430
 1560 RETURN
 1570 REM ..*** TREE SUBROUTINES BEGIN ***
 1580 REM ..SACRED NAMES: N(127),P(385),L(99),N9,P1,P2,P3,P4,P5,P9,
 1590 REM ..              L1,FND,FNN,FNU
 1600 REM ..ARGUMENT: V1,V2,N1,D1
 1610 REM ..N1 IS NAME OF CURRENT NODE (FOR TOP NODE, N1=1)
 1620 REM ..D1 IS NAME OF DAUGHTER NODE
 1630 REM ..NODE NAMES CAN BE ANY NUMBER EXCEPT 9999
 1640 REM ..
 1650 REM ..V1=  0 INITIALIZE TREE; MAKE #1 THE CURRENT NODE
 1660 REM ..     1 ADD D1 AS NEXT DAUGHTER TO CURRENT NODE
 1670 REM ..     2 CUT D1 OFF FROM CURRENT NODE (BUT LEAVE IT AND
 1680 REM ..       ALL BELOW IT)
 1690 REM ..     3 PRUNE D1 (AND ALL BELOW IT) FROM TREE
 1700 REM ..     4 GO UP FROM N1 TO MOTHER NODE (UNLESS AT TOP)
 1710 REM ..     5 GO UP FROM N1 THE WAY YOU CAME (UNLESS AT TOP)
 1720 REM ..     6 GO DOWN TO D1 FROM CURRENT NODE (IF LEGAL)
 1730 REM ..     7 RETURN WITH NEXT DAUGHTER NODE (AFTER D1) IN D1
 1740 REM ..       IF NO MORE, D1=9999
 1750 REM ..       IF D1 ISN"T A DAUGHTER OF CURRENT NODE, RETURN WITH
 1760 REM ..       FIRST DAUGHTER NODE
 1770 REM ..     8 RESET CURRENT NODE TO D1, WHEREVER IT IS IN TREE
 1780 REM ..
 1790 REM ..V2=  2  INSTRUCTION CARRIED OUT, BUT D1 IS A NEW NODE NAME
 1800 REM ..     1  INSTRUCTION CARRIED OUT
 1810 REM ..    -1 CANNOT MOVE UP (OR DOWN) BECAUSE ON TOP (BOTTOM)
 1820 REM ..    -2 MORE THAN 127 NODES
 1830 REM ..    -3 TOO MANY CONNECTIONS
 1840 REM ..    -4 D1 IS NOT A NODE NAME
 1850 REM ..***ENTRY POINT FOR TREE SUBROUTINES
 1860 LET V2=1
 1870 ON V1+1 GOTO 1880,1900,1920,1940,1960,1980,2000,2020,2040
 1880 GOSUB 2070
 1890 GOTO 2050
 1900 GOSUB 2240
 1910 GOTO 2050
 1920 GOSUB 2460
 1930 GOTO 2050
 1940 GOSUB 2590
 1950 GOTO 2050
 1960 GOSUB 3120
 1970 GOTO 2050
 1980 GOSUB 3220
 1990 GOTO 2050
 2000 GOSUB 3330
 2010 GOTO 2050
 2020 GOSUB 3460
 2030 GOTO 2050
 2040 GOSUB 3600
 2050 LET N1=N(P1)
 2060 RETURN
 2070 LET N(1)=1
 2080 FOR P1=2 TO 127
 2090   LET N(P1)=9999
 2100 NEXT P1
 2110 REM ..^ 7530-7550=V1=0= INITIALIZE TREE ^
 2120 LET N9=2
 2130 FOR P1=2 TO 384
 2140   LET P(P1)=P1+1
 2150 NEXT P1
 2160 LET P(1)=0
 2170 LET P(127)=0
 2180 LET P(385)=0
 2190 LET P1=1
 2200 LET P2=1
 2210 LET P9=128
 2220 LET L1=1
 2230 RETURN
 2240 REM ..*** V1=1 ***
 2250 REM ..*** ADD D1 AS THE NEXT DAUGHTER TO CURRENT NODE
 2260 GOSUB 3660
 2270 IF P2>0 THEN 2350
 2280 IF N9=0 THEN  LET V2=-2 ELSE 2300
 2290 RETURN
 2300 LET V2=2
 2310 LET N(N9)=D1
 2320 LET P2=N9
 2330 LET N9=P(N9)
 2340 LET P(P2)=0
 2350 LET P3=P1
 2360 IF FNN(P3)=0 THEN 2380 ELSE  LET P3=FNN(P3)
 2370 IF FNP(P3)=P2 THEN 2440 ELSE 2360
 2380 IF P9=0 THEN  LET V2=-3 ELSE 2400
 2390 RETURN
 2400 LET P(P3)=P(P3)+P9
 2410 LET P3=P9
 2420 LET P9=P(P9)
 2430 LET P(P3)=P2*512
 2440 IF FNP(P2)=0 THEN  LET P(P2)=P(P2)+P1*512 ELSE 2450
 2450 RETURN
 2460 REM ..*** V1=2 ***
 2470 REM ..*** CUT D1 OFF FROM CURRENT NODE (BUT LEAVE IT  & ALL BELOW)
 2480 GOSUB 3660
 2490 IF V2<0 THEN 2580 ELSE  LET P3=P1
 2500 LET P4=P3
 2510 LET P3=FNN(P3)
 2520 IF FNP(P3)=P2 THEN 2540
 2530 IF P3=100 THEN 2580 ELSE 2500
 2540 IF FNP(P2)=P1 THEN  LET P(P2)=P(P2)-P1*512 ELSE 2550
 2550 LET P(P4)=P(P4)+FNN(P3)-P3
 2560 LET P(P3)=P9
 2570 LET P9=P3
 2580 RETURN
 2590 REM ..*** V1=3 ***
 2600 REM ..*** PRUNE D1 AND ALL BELOW IT
 2610 GOSUB 3660
 2620 IF V2<0 THEN 3110
 2630 REM ..* ADD TO FREE LISTS ALL N AND P ENTRIES IN SUBTREE
 2640 IF FNN(P2)=0 THEN  LET N(P2)=9999 ELSE 2680
 2650 LET P(P2)=N9
 2660 LET N9=P2
 2670 GOTO 2960
 2680 LET P(P2)=FNN(P2)
 2690 LET N(P2)=9999
 2700 LET P3=FNN(P2)
 2710 IF P3=0 THEN 2900
 2720 LET P4=FNP(P3)
 2730 IF N(P4)=9999 THEN 2820
 2740 IF FNP(P4)=0 THEN 2790
 2750 REM ..DROP DOWN TO DAUGHTER
 2760 LET P(P4)=P(P4)+(P2-FNP(P4))*512
 2770 LET P2=P4
 2780 GOTO 2690
 2790 LET N(P4)=9999
 2800 LET P(P4)=N9
 2810 LET N9=P4
 2820 REM ..MOVE TO NEXT DAUGHTER
 2830 LET P4=FNN(P3)
 2840 IF P4=0 THEN 2880 ELSE  LET P(P3)=P(P4)
 2850 LET P(P4)=P9
 2860 LET P9=P4
 2870 GOTO 2720
 2880 LET P(P3)=P9
 2890 LET P9=P3
 2900 REM ..GO UP TO MOTHER NODE
 2910 LET P3=FNP(P2)
 2920 LET P(P2)=N9
 2930 LET N9=P2
 2940 LET P2=P3
 2950 IF P2<>0 THEN 2700
 2960 REM ..* DELETE ALL REFERENCES TO PRUNED NODES
 2970 FOR P2=1 TO 127
 2980   IF N(P2)=9999 THEN 3100
 2990   REM ..LOOK AT ALL DAUGHTERS
 3000   LET P3=P2
 3010   LET P4=P3
 3020   LET P3=FNN(P3)
 3030   IF P3=0 THEN 3100
 3040   IF N(FNP(P3))<>9999 THEN 3010
 3050   LET P(P4)=P(P4)+FNN(P3)-FNN(P4)
 3060   LET P(P3)=P9
 3070   LET P9=P3
 3080   LET P3=FNN(P4)
 3090   GOTO 3030
 3100 NEXT P2
 3110 RETURN
 3120 REM ..*** V1=4 ***
 3130 REM ..*** GO UP FROM N1 TO ITS MOTHER NODE (UNLESS AT TOP)
 3140 IF FNP(P1)=0 THEN 3200 ELSE  LET P2=P1
 3150 LET D1=N1
 3160 LET P1=FNP(P1)
 3170 LET L1=(L1-1)
 3180 IF L1>0 THEN 3190 ELSE  LET L1=1
 3190 RETURN
 3200 LET V2=-1
 3210 RETURN
 3220 REM ..*** V1=5 ***
 3230 REM ..*** GO UP THE WAY YOU CAME (UNLESS AT TOP)
 3240 IF L1>1 THEN 3270
 3250 LET V2=-1
 3260 RETURN
 3270 LET L1=L1-1
 3280 IF N(L(L1))=9999 THEN 3250
 3290 LET P2=P1
 3300 LET P1=L(L1)
 3310 LET D1=N1
 3320 RETURN
 3330 REM ..*** V1=6 ***
 3340 REM ..*** GO DOWN TO D1 FROM CURRENT NODE (IF LEGAL)
 3350 GOSUB 3660
 3360 IF V2<0 THEN 3410 ELSE  LET P3=P1
 3370 LET P3=FNN(P3)
 3380 IF P3=0 THEN 3400
 3390 IF FNP(P3)=P2 THEN 3420 ELSE 3370
 3400 LET V2=-1
 3410 RETURN
 3420 LET L(L1)=P1
 3430 LET P1=P2
 3440 LET L1=L1+1
 3450 RETURN
 3460 REM ..*** V1=7 ***
 3470 REM ..*** RETURN WITH NEXT DAUGHTER NODE IN D1 (IF NO MORE, D1=9999)
 3480 IF FNN(P1)=0 THEN 3580 ELSE  GOSUB 3660
 3490 LET P3=P1
 3500 LET P3=FNN(P3)
 3510 IF P3=0 THEN 3530
 3520 IF FNP(P3)=P2 THEN 3540 ELSE 3500
 3530 LET P3=P1
 3540 LET P2=FNN(P3)
 3550 IF P2=0 THEN 3580 ELSE  LET P2=FNP(P2)
 3560 LET D1=N(P2)
 3570 RETURN
 3580 LET D1=9999
 3590 RETURN
 3600 REM ..*** V1=8 ***
 3610 REM ..**: RESET TO NODE D1
 3620 GOSUB 3660
 3630 IF V2<0 THEN 3650 ELSE  LET P1=P2
 3640 LET L1=1
 3650 RETURN
 3660 REM ..*** FIND POINTER FOR D1
 3670 IF D1=9999 THEN 3760
 3680 IF P2<1 OR P2>127 THEN 3700
 3690 IF N(P2)=D1 THEN 3780
 3700 IF D1<1 OR D1>127 THEN 3730
 3710 IF N(D1)=D1 THEN  LET P2=D1 ELSE 3730
 3720 RETURN
 3730 FOR P2=1 TO 127
 3740   IF N(P2)=D1 THEN  EXIT 3780
 3750 NEXT P2
 3760 LET V2=-4
 3770 LET P2=-1
 3780 RETURN
 3790 PRINT TAB(9);"+*+ The CAVES are closed +*+"
 3800 END