So far, you have created a fairly typical NAMES file containing names and addresses, and a simple GET.NAMES update program for maintaining that file. Together, they form a rudimentary mailing list application that might be found on any Pick system. The next step is to start using B-TREE-P subroutines to create B-trees, so that the mailing list can be sorted and searched in a convenient manner.
One of the most important B-TREE-P programs is a subroutine named BTPINS, short for B-TREE-P Insert. Give the command EDIT BP BTPINS in order to enter the Editor and type in the following source code for BTPINS:
BTPINS
001 SUBROUTINE BTPINS(ROOT,SIZE,BFILE,DFILE,ID,ITEM)
002 UID = ID
003 CALL BTPKEY(ROOT, UID, ITEM, KEY)
004 FK = KEY
005 READ NID FROM BFILE, ROOT ELSE
006 READ NID FROM BFILE, "NEXT.ID" ELSE NID = 0
007 WRITE (NID+1) ON BFILE, "NEXT.ID"
008 WRITE NID ON BFILE, ROOT
009 WRITE "" ON BFILE, NID
010 END
011 BU = 0
012 NP = ""
013 100 READ N FROM BFILE, NID ELSE STOP "BTP1"
014 L = 0 ; R = N<1>+1
015 IF R = 1 THEN P = 1 ELSE
016 LOOP
017 P = INT((L+R)/2)
018 IN = N<2, P>
019 IF IN = UID THEN
020 CRT "Already inserted!"
021 IF BU THEN STOP "BTP2" ELSE RETURN
022 END
023 READ IT FROM DFILE, IN ELSE STOP "BTP3"
024 CALL BTPKEY(ROOT, IN, IT, KEY)
025 IG = (FK > KEY)
026 IF IG THEN L = P ELSE R = P
027 UNTIL (R-L) <= 1 DO REPEAT
028 IF IG THEN P = R
029 END
030 NNID = N<3, P>
031 IF (NNID # "") AND NOT(BU) THEN
032 NID = NNID
033 GO TO 100
034 END
035 N = INSERT(N, 2, P, 0, UID)
036 IF BU THEN N = INSERT(N, 3, P+1, 0, NP)
037 N<1> = N<1>+1
038 IF N<1> <= (2*SIZE) THEN WRITE N ON BFILE, NID ELSE
039 LOOP
040 READ NP FROM BFILE, "NEXT.ID" ELSE NP = 0
041 WRITE (NP+1) ON BFILE, "NEXT.ID"
042 READ NN FROM BFILE, NP ELSE NN = ""
043 UNTIL NN = "" DO REPEAT
044 J = 1
045 FOR I = (SIZE+2) TO ((2*SIZE)+2)
046 IF N<2, I> # "" THEN NN<2, J> = N<2, I>
047 CID = N<3, I>
048 IF CID # "" THEN
049 NN<3, J> = CID
050 READ C FROM BFILE, CID ELSE STOP "BTP4"
051 C<4> = NP
052 WRITE C ON BFILE, CID
053 END
054 J = J+1
055 NEXT I
056 NN<1> = SIZE
057 NN<4> = N<4>
058 WRITE NN ON BFILE, NP
059 UID = N<2, SIZE+1>
060 NN = SIZE
061 FOR I = 1 TO (SIZE+1)
062 IF I <= SIZE THEN NN<2, I> = N<2, I>
063 IF N<3, I> # "" THEN NN<3, I> = N<3, I>
064 NEXT I
065 NN<4> = N<4>
066 WRITE NN ON BFILE, NID
067 IF NN<4> # "" THEN
068 BU = 1
069 NID = NN<4>
070 GO TO 100
071 END
072 LOOP
073 READ RID FROM BFILE, "NEXT.ID" ELSE RID = 0
074 WRITE (RID+1) ON BFILE, "NEXT.ID"
075 READ NN FROM BFILE, RID ELSE NN = ""
076 UNTIL NN = "" DO REPEAT
077 NN<1> = 1
078 NN<2> = UID
079 NN<3, 1> = NID
080 NN<3, 2> = NP
081 WRITE NN ON BFILE, RID
082 WRITE RID ON BFILE, ROOT
083 READ NN FROM BFILE, NID ELSE STOP "BTP5"
084 NN<4> = RID
085 WRITE NN ON BFILE, NID
086 READ NN FROM BFILE, NP ELSE STOP "BTP6"
087 NN<4> = RID
088 WRITE NN ON BFILE, NP
089 END
090 RETURN
091 END
At this point, don't worry about trying to understand how BTPINS works. It has been coded in such a way that it will never have to be modified by you, regardless of the application that will be using your B-trees or the way in which you will be doing searching and sorting of your files.
Compile BTPINS. Once BTPINS has been successfully compiled, catalog the program with the command CATALOG BP BTPINS, since most Pick systems require that subroutines be cataloged. Similarly, edit, compile, and catalog the following BTPKEY subroutine:
BTPKEY
001 SUBROUTINE BTPKEY(ROOT, ID, ITEM, KEY)
002 EQU nul TO CHAR(0)
003 BEGIN CASE
004 CASE ROOT = "ZIP" ;* By zip/adr/comp/lname/fname/id
005 KEY = ITEM<6>:nul:ITEM<4>:nul:ITEM<3>:nul:ITEM<2>:nul:ITEM<1>:nul:(ID"R#10")
006 CASE ROOT = "COMP" ;* By company/lname/fname/id
007 KEY = ITEM<3>:nul:ITEM<2>:nul:ITEM<1>:nul:(ID "R#10")
008 CASE ROOT = "LNAME" ;* By lname/fname/id
009 KEY = ITEM<2>:nul:ITEM<1>:nul:(ID "R#10")
010 CASE 1 ; STOP "BTP7"
011 END CASE
012 RETURN
013 END
BTPKEY is called by BTPINS, and controls the way in which your files will sort. By changing the statements inside BTPKEY, you can design B-trees that allow you to sort and search your files in any order you want. For now, just leave BTPKEY exactly as listed above.