Information  about  the  unit trees.pas writen by Andrei Korobeinik and Dmitri
Lepp. The unit is made to work with 'trees' - a kind of data structures.

			SPECIFICATIONS

The structure of the input file.
 The  input  file  consists  of  n lines. At each line there is an information
 about	one node of the binary tree. It looks like
 A B C D<enter>
 or
 A B C D E<enter>
 so E is an optional parameter. All the elements are separated by exactly one
 blank.
 A  -  integer (not 0!). It is an unique label of the current node (i.e the
  label of its line). Won't be used in the program.
 B - integer. The 'key' value of the node.
 C - integer. It is the label of the left child of the node. If 0, then the
  left child of this node is missing.
 D - integer. It is the label of the right child of the node. If 0, then the
  right child of this node is missing.
 E  -  string of length <= MAX_INFO (set to 20). Contains the additional info
  for the node. The deafult value (if E is missing) is an empty string.

The structure of representation in memory.
 The  representation  of  a binary tree of n nodes consists of n records. Each
 record contains 6 fields:
 key - integer. The 'key' value of the node.
 left  -  pointer  to  the left child of the node (or NIL if the left child is
  missing).
 right - pointer to the right child of the node (or NIL if the right child is
  missing).
 str_info - string of length <= MAX_INFO (set to 20). Contains the additional
  info for the node.
 x - integer. A field of free use (any informational for the node).
 y - integer. A field of free use (any informational for the node).


			DESCRIPTION

The unit contains four functions and procedures. To do with it, print 'uses
trees;' in the beginning of the program and you can include into your program
all the functions and procedures described below. Example of the input file is
in  inp.txt. Example of the unit's usage is in demo.pas. The tipe of a pointer
to any node (to the root of tree, for example) is pnode.

function ReadBinaryTree(filename:string):pnode. Reads data about the binary
tree from the input file (filename) and converts it into the structure in
memory	(read	specifications). Returns  the pointer to the root of the tree
(or NIL, if the tree is empty). Assumes that the input file can't contain more
than MAX_N lines (set to 1000).

procedure  WriteBinaryTree(filename:string,tree:pnode). Writes the binary tree
(tree  -  pointer  to its root) from memory to the output file (filename) with
format described before.

function  DisplayBinaryTree(tree:pnode,left,height:integer):integer.  Displays
the  binary  tree  (tree - pointer to its root) at the screen. Parameters left
and height are coordinates of the beginning of the output.

procedure DisplayTree(tree:pnode). Displays the usual tree at the screen. Uses
its  binary  representation  from  memory  (tree - pointer to the root of this
binary tree). The output begins in the left higher corner. The children of any
node are all the nodes which lie at the next lower line from this node, to the
right of it and to the left of its right collegue.

			ERRORS MESSAGES

There  are  some  errors  which  can  be processed by unit. All the others are
checked  by  Pascal  or won't be checked at all. To get the code of the errors
described below, use DOS unit (they can be returned by HALT).

1: Error opening input file!
 Something wrong with the input file. Wrong name, for example...
2: Wrong reference to a!
 Error	in  the  input file. There is a pointer to the node with number a, but
 the node doesn't exist.
3: The tree is too high!
 and
4: The tree is to wide!
 There	is  not  enough  place	at  the  screen  for  the  tree in DisplayTree
 procedure.
5: Error opening output file!
 Something  wrong  with your disk. Not enough place, for example, or you can't
 write to this disk.