Program title:	Binary Trees Demo
Written by: (I got it from ZUG disc 14, and Ray Penley did the work)
            (Buddenberg)
Date written:	November 1981

Last edited:	June 1982 rab

Pascal compiler: Pascal/Z vers 4.0, Ithaca Intersystems, Inc.

Summary:	Maintain a sorted list in a binary tree

Bibliography:
  GROGONO, P.: Programming in PASCAL, Addison-Wesley Publishing Co.,
	Reading, MA.
  TENENBAUM, A. and AUGENSTEIN, M.: Data Structures Using Pascal,
	Prentice-Hall, Englewood Cliffs, N.J. 07632
  WIRTH, N.: Algorithms + Data Structures = Programs, Prentice-Hall,
	Englewood Cliffs, N.J. 07632

Notes to latest edition.  by Rex A Buddenberg

1.  Program broken up into modules for separate compilation.
My editor gets cantankerous with files larger than its buffer,
and the "disc" module took a lot of troubleshooting to get
it working properly.
     The modules are named:
BTREE	the main program
DISC	procedures for reading and writing the leaves to disc file
ORDER   three procedures, PRE-, POST-, and IN-ORDER for traversing
	the tree.  
DELETE  the delete procedures for removing a record from the tree
	and relinking what is left.
MENU	utility routines including MENU and HELP.

2.  Added options 4,5, and 8 to the menu.  Store and Fetch are
the significant "improvements".  They allow writing the tree
out to disc and later recovering it.  Thus the data contents can
be preserved.  The user can now customize the insert and list
routines to make a practical program.

3.  A couple glitches.  When loading a data file from disc, you
will get a bell and a note that that record already exists
on the tree.  No harm done, but a GOTO is needed in the FETCH
procedure to jump out of the loop on End-Of-File.
    Having some problem with the DELETE feature.  Some flexibility
here in finding records on, say, the first 10 characters rather
than the whole record might make things easier.

4.  Things remaining.  Several further developments can be
implemented, but most of the hard work is done.  Some ideas:
	- add some data checking to the insert routine.  To do
	this, I would suggest making a separately compiled procedure,
	rather than leaving it in the main program block.
	- add an option to search through the file looking for
	some field other than the key.  Speed sacrifices are
	certainly entailed, but the flexibility would be enhanced.
	As records are stored in-memory rather than on disc, the
	speed of search still should be fairly quick.
	- expand the HELP command usefulness.  Adding code to
	allow calling from several different procedures would
	allow the operator to check up on instructions at opportunity
	rather than solely from the master menu.
	- allow sorted listing to D)isk as well as C)onsole and
	P)rinter.  Note that this should not be used for data
	storage, but for output storage.  To be efficient, Btrees
	should be balanced.  Data placed on the tree in order
	will result in a lopsided tree - essentially a linked list.
	Things will work ok, but the efficiency and speed of the
	tree structure is lost.
	- some reformatting of the P)rinter routine would allow for
	printing on either labels, index or rolodex card stock.
	If the blank "2nd address line" still is omitted, you gotta
	put in another linefeed somewhere to compensate.
	- the insertion SORT program on Disc 16 can easily be
	adapted to sort the data files created by this tree
	program into order by a different field.  You lose a bit
	of interactiveness, but if you are making cross reference
	lists, that's not a problem.
	- enhance the DELETE routine to find the to-be-deleted
	record, display it and ask if that is the record to go.
	This could also be further enhanced to allow changes
	in data fields(so long as the key is not changed) and
	replacement on the tree.

.