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Pascal NewsLetter
Issue #2
May, 1990
Editor: Pete Davis
The Programmer's Forum BBS is the home of
PNL. It can be reached in Washington, DC at
(202)966-3647. Information is available
through the following locations:
FidoNet: Pete Davis@1:109/138
GEnie: P.DAVIS5
BitNet: HJ647C@GWUVM & UE356C@GWUVM
InterNet:
HJ647C@GWUVM.GWU.EDU &
UE356C@GWUVM.GWU.EDU
Table of Contents
Introduction ........................... Page 3 (Pete Davis)
Making the Point with Pointers ......... Page 5 (Pete Davis)
Neat Use of Object Files ............... Page 16 (Craig Thurber)
For Beginners .......................... Page 22 (Bob Gowans)
Conclusion ............................. Page 29 (Pete Davis)
Notice ................................. Page 32 (Pete Davis)
Distribution List ...................... Page 33 (Pete Davis)
Turbo Pascal is a registered trademark of Borland International
2
Introduction
Well, school is over and it's time for the second issue of
PNL. I would first like to thank Robert Garcia in Edinburgh (did
I spell that right?) Texas. He was the first person to give me a
response. His praise alone would have been enough for the second
issue to come out. He also gave me the idea for an article on
pointers for beginners. I had overlooked that, so here it is.
Secondly, I would like to thank Craig Thurber, the author of
'Neat Use of Object Files' and Bob Gowans, the author of the 'For
Beginners' column. I really liked the articles and learned
something new. Thanks Craig and Bob, feel free to contribute any
time.
I would like to point out that I am really open to
submissions. Please, if you write an article, send it to us. I
can't guarantee when or if it will go in, but it can't hurt to
try. It takes some of the load off of my shoulders.
One subject that I would really like to see covered in PNL,
is Object Oriented Programming in Turbo Pascal. This is one
subject I will have to leave to others, at least for now, as I am
not really fluent in it yet. So, if you're a hot-shot with OOP,
please submit an article. It would be very beneficial to a lot of
people, including me.
3
I would really just like to thank everyone that I've heard
from. Your compliments, suggestions, and comments are what makes
this worth doing. I hope to have the PNL going for as long as I'm
computing.
Oh yeah, and one last thing. The release of PNL might be a
little sporadic. Maybe after a while I'll start setting some kind
of time period up, but right now, it's whenever I get the time.
I'm hoping to be able to do it more than once a month, if time
allows. I really do enjoy writing this.
Well, until the next issue, thanks, and please try to pitch
in: be it an article, a suggestion, or just passing this file
around to your local bulletin board. All of this helps.
_Pete Davis
4
Making the Point with Pointers
Those of you familiar with C are probably very comfortable
with pointers. That's understandable, you can't program in C
without pointers (well, you can, but not well). Well, those of us
that started on Pascal have a little more trouble understanding
them. Part of the problem is that pointers seem almost foreign to
the ideas and methods of programming in Pascal. In fact, until
getting involved in more advanced programming, one can usually
get away without using pointers at all. So, why use pointers?
Well, there are several reasons. For one, and probably most
important, it gives you access to the heap, all that extra memory
you have in a 640K machine that you normally can't use. In Turbo
Pascal, you are limited to 64k for any single data structure.
This is a pretty severe limitation when you are working with,
say, a database, or a word processor. Secondly, there are quite a
few structures that are more difficult to work with without
pointers, for example, a binary tree.
There are a multitude of structures that pointers make
possible. Covering every single one of them would be almost
impossible. To make things a little more reasonable, I will cover
the basic concept of pointers, and then the most common use of
them: The linked list. I will leave coverage of other structures
to future releases of PNL. In PNL001, there was an article:
Generic Structures in Turbo Pascal, which covered a simple stack,
5
using pointers. It was a more complicated version of a stack,
actually, but the same ideas prevail for other structures. I will
present a linked list with several operators. I will also include
source code to the Linked List unit itself and then in the
article on Sorting, I will include some sorting routines to
manipulate our linked list.
Think of a linked list as a chain. Each link in the chain
contains some data. At the end of that link is another link with
more data. You can add links to your chain and you can take them
off. If you take a link out of the middle, you have to re-
connect your two chains to make a single chain. This is the basic
premise for linked lists. Depending on how you want your data
ordered (if you even want it ordered) decides how you insert your
data. If you want a stack, you always add a link at the beginning
of your chain. If you want a queue, you always add a link at the
end of your chain. If you want a non-ordered linked list, you
could do either. If you want an ordered linked list, though, you
have to go through your list, find out where your link goes, and
insert it between two other links. (unless it's the lowest or
highest value in the list)
Below is a small diagram of a linked list. Following it is a
short explanation.
6
Node 1 Node 2 Node 3
+----------+ +----------+ +----------+
| Data | +--->| Data | +--->| Data |
| Item 1 | | | Item 2 | | | Item 3 |
+----------+ | +----------+ | +----------+
| Pointer |----+ | Pointer |----+ | Pointer |-->NIL
+----------+ +----------+ +----------+
Each node in our list contains two things: A Data Item,
which the programmer can decide on: A record, a string, an
integer, etc.. Any data type will do. The second item is a
pointer. The pointer points to the location in memory of the next
node in the list. The two nodes don't have to be anywhere near
each other in memory, but as a programmer, they will appear to be
right next to each-other. Notice the NIL in the pointer in Node
3. This is a reserved value in pascal that indicates that the
pointer is pointing to nothing. In our case, it signifies the end
of the list.
Now, we are missing one item in our list, and that is the
pointer to the beginning of the list. This is something that you
must have, otherwise you won't know where in memory your list is.
First, let's create our sample record and pointer:
type
Samp_Ptr = ^Samp_Rec; { A pointer to a Samp_Rec record }
Samp_Rec = record { Our Samp_Rec record type }
SampData : integer; { Data can really be anything }
Next_Rec : Samp_Ptr; { Pointer to next item in list }
end;
7
Ok, Samp_Ptr is a pointer to data of type Samp_Rec. You make
a typed pointer by including the '^' before the data type that
you want to point to; in this case Samp_Rec. Notice that Samp_Ptr
is declared before Samp_Rec, yet Samp_Ptr is a pointer to type
Samp_Rec. The reason for this is so that the Next_Rec pointer can
be declared, making linked lists possible.
Now, to help give us something to work with, I'll show the
initialization procedure, and then go into a bit of explanation
about how it works.
procedure Init_Samp_List(var Head : Samp_Ptr);
{ notice in our initialization that a record of type Samp_Rec is
never defined nor used! }
begin
Head := nil;
end;
First of all, notice that in our initialization we are
passing a pointer of type Samp_Ptr, and not an actual record. It
must also be passed as a variable parameter, as the variable Head
will be given it's initial value and that value must return to
the main program. The only code in this procedure is to assign
the pascal reserved value of nil to Head. Head means the head of
the list, or the first link in the list. nil is a variable name
supplied by pascal which means that there is not value assigned
to the variable. In our case, it means that our list is empty.
8
Now, I want to supply a simple insert procedure to insert a
single value into the list. This will give us a little picture of
how to manipulate our data with pointers. The insert procedure I
am providing here inserts a value into the beginning of the list.
In the Turbo Pascal Unit, enclosed, you will find three insert
procedures: Insert_End, Insert_Begin, and Insert_In_Order. I'll
leave Insert_Before, and Insert_After for you to write. They way
they are supposed to work is that Insert_Before will insert a
record right in front of the current record you are pointing to.
To accomplish this, you need to pass two items: The head, so you
can go through the list again to find out what the record is
before the current record, and the current record, of course.
Insert_After is a little easier, in all that needs to be passed
is the current record. The record you insert should end up
pointing to the record that was right after the current record,
and the current record should end up pointing to the one you
insert. One would rarely need this many insert procedures, in
fact, one is usually enough. So, on with our Insert_Begin
procedure:
procedure Insert_Begin(var Head : Samp_Ptr;
Data_Value : integer);
var
Temp : Samp_Ptr; { A temporary variable to work with }
begin
{ Allocate memory for a Samp_Ptr }
new(Temp);
9
{ Temp will become the first record and Head will become
the second record in the list. But, we have to do things
kind of backwards, so first: Make head the second record }
Temp^.Next_Rec := Head;
{ Now that Temp^.Next_Rec has a pointer to where the second
record is, we can now change the value of Head so that it
will be at the head of the list. }
Head:= Temp;
{ Next we need to put the value in this first record, that
the user has provided to us. }
Head^.SampData := Data_Value;
end; {All done}
Here's what's going on: First of all, the new command is
used to allocate some space on the heap for our data. The new
procedure returns the memory location of this space in the
variable Temp. Instead of directly using a Samp_Rec data type, we
use the pointers Temp and Head to access the fields in our
reserved space. To do this, the general construct is:
POINTER^.FIELDNAME
One can assign something to this place or receive a value
already stored. For example, to find the contents of SampData for
the first record in the list we could do the following. (Assume
that OurInt was previously defined as an integer.)
OurInt := Head^.SampData;
or we could change the contents by writing:
Head^.SampData := OurInt;
The most important step and the one that seems to cause the
most problems for programmers unfamiliar with pointers, is
10
maintaining and traversing the links in our list. Noticed what we
did in our Insert_Begin procedure - If we are using a new list,
then Head is going to have a value of nil :
Head-> Nil
First of all, we allocate some memory for the record and
then assign the value of head to Temp^.Next_Rec :
+----------+
| SampData |
Temp -> | undefined|
+----------+
| Next_Rec |
| Nil |
+----------+
Next we assigned Head to be equal to Temp:
+----------+
Head -> | SampData |
Temp -> | undefined|
+----------+
| Next_Rec |
| Nil |
+----------+
After that, we had to assign the value to SampData. Suppose
we passed the value of 4:
+----------+
Head -> | SampData |
Temp -> | 4 |
+----------+
| Next_Rec |
| Nil |
+----------+
11
That takes care of our first value, but what about the
second value? How does that work? Well, if we follow the same
steps as before, let's see where it leaves us. Let's say we're
going to insert a value of 12 this time. First of all we need to
allocate space and Temp will be pointing to that space, then we
assign Temp^.Next_Rec to Head:
+----------+ +----------+
| SampData | | SampData |
Temp -> | undefined| +-----> | 4 |
+----------+ | +----------+
| Next_Rec | | | Next_Rec |
| Head |----+ | Nil |
+----------+ +----------+
Now, we assign the value of Head = Temp. That will move Head
to the beginning of the list.
+----------+ +----------+
Head -> | SampData | | SampData |
Temp -> | undefined| +-----> | 4 |
+----------+ | +----------+
| Next_Rec | | | Next_Rec |
| -------|----+ | Nil |
+----------+ +----------+
Now we assign the value of Data_Value (12) to the SampData
field.
+----------+ +----------+
Head -> | SampData | | SampData |
Temp -> | 12 | +-----> | 4 |
+----------+ | +----------+
| Next_Rec | | | Next_Rec |
| -------|----+ | Nil |
+----------+ +----------+
12
That just about does it for the insert procedure. It's a
very difficult concept for beginners to understand and that's why
I am supplying all of the diagrams. I want to make the concept of
pointers themselves as clear as possible. Once you understand the
concept, the different operations on them become easy. If at this
point you still don't understand, I suggest that you reread from
the top of the article and give it another try. If at that point
you still don't understand, try putting it away for a day or two
and try again. I find that putting a difficult concept away for a
little while and coming back to it makes it easier to understand.
Like the insert operations, the delete operations come in
all shapes and sizes. The accompanying unit contains the
following: Pop_First (for stack use), Pop_Last(for queue) and
Delete_Here. Again, I will leave Delete_Before and Delete_After
for you to write. With the three I provide, it should be fairly
simple. These are more than enough for the typical linked list.
The main problem with doing the delete is that you have to find
out where you are in the list before you can take any action. If
you want to delete the first node in the list, then you have to
re-assign the Head of the list to the second item in the list. If
you want to delete something from the end of the list, you need
to make sure that the Next_Rec field is set to Nil in the last
record. If you want to delete something in the middle of the list
then you have to reconnect to second half of the list to what's
left of the first half.
13
Using our first diagram:
Node 1 Node 2 Node 3
+----------+ +----------+ +----------+
| Data | +--->| Data | +--->| Data |
| Item 1 | | | Item 2 | | | Item 3 |
+----------+ | +----------+ | +----------+
| Pointer |----+ | Pointer |----+ | Pointer |-->NIL
+----------+ +----------+ +----------+
If we take out Node 2, we have to assign the pointer in Node
1 to point to Node 3. If we get rid of Node 3, we need to have
the Pointer in Node 2 be nil.
Node 1 Node 2 Node 3
+----------+ +----------+ +----------+
| Data | X--->| Data | X--->| Data |
| Item 1 | X | Item 2 | X +->| Item 3 |
+----------+ X +----------+ X | +----------+
| Pointer |--+-X | Pointer |----X | | Pointer |-->NIL
+----------+ | +----------+ | +----------+
+------------------------+
This brings up the need for one more procedure provided in
pascal, and that's the dispose procedure. The dispose procedure
returns whatever space you have allocated back to the heap so
that it can be reused. You don't always have to do that, but if
you are working with a lot of data and you get rid of links
without using the dispose procedure, you are more likely to run
out of heap memory. I will let you look at the source code for an
example of the dispose procedure.
I'm going to have to keep myself from including more code
examples in the magazine, and instead let you see the unit that
is included with this issue. It has all the necessary procedures
and functions, and then some. Each one has a description as to
14
it's function. I don't feel that further explanation here would
be beneficial. In other words, I'm out of breath and thought. I
don't know what else I could tell you.
I hope this article has been helpful, and if anyone feels
that I've missed something important, I'll do a follow-up article
on it. I will be showing other uses of pointers in other issues,
but it is unlikely that I will keep it this basic, unless demand
keeps things at this level.
15
NEAT USE OF OBJECT FILES
by Craig Thurber
Not long ago I wanted to do something simple: include a
downloadable soft font file in a compiled Pascal .EXE file. This
seemed like an easy thing to do, but alas, I could not find
anything in my documentation or reference books that gave an
indication of how to do it. It wasn't long before some of the
fine users of this language pitched in and provided an answer to
the problem. The answer has proven to be a neat use of object
files. The inclusion of text or other types of files in the .EXE
forms has a number of advantages, the most notable of which is a
very quick access to what might otherwise be a separate disk
file. Since the equivalent of the disk file is already loaded
into memory, there is no need to wait for a floppy disk file to
be accessed.
The method and some examples are presented below. Many
thanks to Juan Jimenez for both his insights into this problem
and his patients in providing an answer for which I had no more
questions. Juan answered the message that I posted in the GEnie
Borland Roundtable. If you are interested in a very fine
service, please consider this one*.
External Procedure Calls
------------------------
External procedures can be declared and called in the Pascal
16
language. The user manual suggests that this capability was
included in the language primarily for inclusion of assembly
language routines in the compiled versions of Pascal programs.
However, the call to an external procedure can also be used to
move the contents of a text or other type file to a Pascal
pointer location, and then to perform standard Pascal operations
with the data that resides at that pointer location. Declaration
of an external procedure call is made with the following
statement in a Pascal program or unit:
procedure HelloJuan; external; {$L HELLO.OBJ}
In the above example, the external file named HELLO.OBJ will be
included in the compilation of the .EXE file. The {$L} compiler
directive is the local symbol information directive. Note that
this compiler directive is ignored if the Debug Information
setting {$D-} is set to off.
The overall effect of this declaration is that the external
object file named HELLO.OBJ is recorded in the .TPU or .EXE file
at the time of compilation. While this inclusion will increase
the size of these files, it does not slow program execution.
Creation of Object Files
------------------------
Object files are created with the BINOBJ.EXE utility that is
provided with Turbo Pascal. The procedure involves invoking the
BINOBJ.EXE procedures with a designated file for conversion and
17
an external name to give to the file. In the case shown above,
the test file HELLO.TXT would be converted to the object file
HELLO.OBJ having the external procedure call HelloJuan with the
following command (assuming the given drives and directories):
C:\TP\BINOBJ A:\HELLO.TXT A:\HELLO.OBJ HELLOJUAN
When creating object files, keep track of the original file size.
You will need it later when you invoke them in a Pascal
procedure.
Using the External Procedure
----------------------------
Suppose that you started by declaring the above procedure
after converting the file HELLO.TXT to the object file HELLO.OBJ.
The original text file contained the statement "Hello, Juan.",
which is 13 characters long. After conversion to an object file,
be sure not to confuse the byte size of the object file with the
size of the original text file; it is the size of the original
file that you will need while writing the Pascal code. Suppose
also that the objective of your programming is to send the
statement "Hello, Juan." from the compiled .EXE file to the
printer. Here is the code that will do this, as a complete
program. Each statement in the program is explained below.
program Hello;
uses Printer;
procedure HelloJuan; external; {$L+ HELLO.OBJ}
18
var PtrStr : Pointer;
OutString : String;
begin
PtsStr := @HelloJuan;
Move(PtrStr^,OutStr[1],13);
OutStr[0] := Chr(11);
Writeln(Lst,OutStr)
end.
The result of running this file will be printing the words
"Hello, Juan" on the printer that is located at LPT1.
As nice a fellow as Juan is, I don't suppose that making
your printer say hello to him is very useful to you. So here is
another example. Suppose you want a full screen of text to
appear instantly. You have written programs that make a call to
an external file and have watched them slowly write one line at a
time down the screen; you have had enough of this and you want
the speed that Pascal normally shows. Well, this could be the
answer. Write your text file, note the length of it (I'll use
2000 here) and then change the above program as shown below. For
purposes of this article, I have assumed that the file names and
external declarations are the same; the only difference is that
you are now writing a nice letter to Juan and you want it to
appear on the screen very quickly. Here is the procedure code
that will do it:
procedure HelloJuan; external; {$L HELLO.OBJ}
const Size = 2000;
19
var PtrStr : Pointer;
OutStr : Array[1..2000] of Char;
Index : Integer;
begin
PtrStr := @HelloJuan;
Move(PtrStr^,OutStr[1],Size);
For Index := 1 to Size do
Write(OutStr[Index])
end;
What's That Code All About?
---------------------------
Here is what the coding is all about:
Variable declarations: PtrStr is a generic pointer. It is
used to mark the starting location of the compiled external file.
OutStr is an array that is large enough to hold the contents of
the externally declared procedure. Index is a simple counter
that is used to track the feeding of each character of the
compiled external file to the screen.
PtrStr := @HelloJuan; : This statement moves the pointer to
The start of the procedure that was named HelloJuan during the
conversion of the text file to an object file.
Move(PtrStr^,OutStr[1],Size);: This statement moves the
number of bytes specified by Size from the starting location
specified by PtrStr^ to the first element of the array OutStr.
20
For Index ... do : This loop dumps the array OutStr to the
screen one element at a time. The resulting screen dump will
appear exactly as the original text file was written.
What Else Does It Do?
---------------------
The conversion of files to object files and inclusion of
them in the executable form of a program offers a wide variety of
opportunities for programmers. In principle, any file that you
can present on the screen or printer can be converted to an
object file and then included in the .EXE file during
compilation. When the procedure is called using the above
techniques, the results will be very quick and will be an exact
duplicate of what you would get by other means. So if you want
to have a fast way of accessing help files, graphics or other
files, give the method a try.
* A GEnie account can be obtained by calling 1-800-638-9636.
21
For Beginners
By Bob Gowans
Where to start? A good question - the beginner's column is
aimed at people with little or no programing experience of
Pascal and will start at a very basic level but will graduate
(hopefully) to more complicated programming routines as our
confidence in the use of Pascal increases. With this in mind I
would appreciate any feedback on my articles - suggestions,
constructive criticism and especially any neat programing tricks
that beginners would find useful. I will give details on contact
addresses at the end of this article.
Pascal has to be taught in a way that encourages good
programing. As a high-level language it is structured in this
way and can allow the Pascal programer to present his programs in
a manner of clarity that is almost unparalleled by other
high-level languages. So if you have just bought the latest
version of your favorite Pascal compiler and your fingers are
itching to get at the keyboard to write that ultra program you
have always wanted to produce to impress your friends, wife,
boss? Then stop! Good programs take a lot of thought and
planning before you reach the actual coding stage. In fact, an
English language equivalent of your program should first be
produced, showing step by step what your program does. Moreover
this English language version should be able to make clear, to
22
non-programers, exactly what your program is going to do. This
may not be essential for the relatively small programs which we
will encounter at this stage but it is an invaluable technique
when writing large programs (such as the impressive ultra
program) and as an aid to problem solving. It is well worth
while getting into the habit of using this method known as
TOP-DOWN design to plan you programs. In future articles it is
hoped that I will be able to introduce this method but meanwhile
lets get back to those itching fingers and get on with some
program writing. The programs given as examples are standard
Pascal, that is they should compile using any Pascal compiler,
however I have only used Turbo Pascal V4 to try them out and test
them. Here is a simple but complete Pascal program:
program hello_there; { This is our first program }
begin
write('Hello');
writeln(' my name is Bob');
write('How are you?')
end.
Lets break this program down to it's component parts and
examine each part in turn. The program starts with the word
program followed by a space followed by the program name. In this
case the name is hello_there but subject to some rules, it could
be anything we chose, however it is good programing practice to
chose a name that is relevant to what the program does. Such
names are given the term IDENTIFIERS.
Rules for identifiers:
23
1) An identifier must begin with a letter.
2) They may then consist of letters and digits, upper or
lowercase letters are treated as identical.
3) They can contain embedded underscore characters to improve
readability as has been done in our example program identifier -
hello_there.
4) They can be of any length but generally speaking the compiler
will ignore anything following the first 8 identifier characters.
Examples of Identifiers:
accounts A386XT Income_Tax BUDGET1990
Try this self-test, the answers are given at the end of
the article.
Which of the following are valid identifiers:
a) FirstRun
b) Mississippi
c) Locust12
d) George Washington
e) Program
f) 123go
g) accounts.1990
24
By the way, reserved words, that is words that the Pascal
language itself uses, cannot be used as valid identifiers. The
complete list of Pascal reserved words should be found in your
manual or any decent book on Pascal.
Going back to our program, the program heading (Program
hello_there;) has a semi-colon at the end of the line. The
program heading does not contain any actual commands it simply
marks the beginning of the program. Program commands come between
the Pascal reserved words begin and end, they are often referred
to as the statements part of the program and each statement line
is separated by a semi-colon(;). The statements part of the
program contains a series of instructions for the computer to
execute. Our example program contains statements designed to
write output to the screen. To write a line of output
the standard output procedure writeln, the form is
writeln('textout').
Writeln and write are very similar in what they do but
writeln has the advantage of performing a carriage return so
your next writeln statement would write out text on a new
line. Try the program and make sure you understand the
differences between write and writeln. Note that each statement
in the statements part is separated by a semi-colon
except the one preceding the reserved word end and that the
final end in the program is followed by a period. Finally on the
25
program heading line you will have noticed that there is a
comment in curly brackets. You can place comments at strategic
points in your program to add clarity. Comments will help you
when you want to amend you programs after you have not used
them for some time they will show what your intention was at
the time you wrote the program, something you may have
forgotten as time goes by. The rule is you can place comments
at relevant points in the program as long as they are placed
within curly brackets. Here are some more examples for you to
try:
program Name_and_address;
{ writes to the screen your name and address }
begin
writeln('My Initials Surname');
writeln('Department of Computer Science');
writeln(' The University');
{ note the use of spaces for output }
writeln(' City');
writeln(' Country')
end.
Writeln is handy for inserting blank lines so that your text
output looks better
program nice_lines;
begin
writeln('Line one');
writeln; { inserts a blank line }
writeln('Line three')
end.
Just to get you thinking, write a Pascal program that
would produce the following output to the screen:
'How many times have I told you, don't do that'; she said.
26
Clue - watch the quotation marks!
TIP - If you are using Turbo Pascal there is a neat routine
provided to clear the screen. It can be implemented as follows:
program clear;
uses crt; { this must be here and is for turbo pascal only }
begin
clrscr; { turbo pascal clear screen routine }
...........
...........
end.
I hope you have found this article helpful in the next issue
I hope to discuss variable types found in Pascal, more about
top-down design and provide more tips. I will also provide a
solution to the exercise. In case you cannot wait and are pulling
your hair out in frustration you can contact me at the following
Email addresses for the solution. I would also be pleased to help
beginners with Pascal programing problems as well.
JANET - MCGDRKG@UK.AC.MCC.CMS
INTERNET - MCGDRKG%MCC.CMS.AC.UK@CUNYVM.CUNY.EDU
EARN/BITNET - MCGDRKG%MCC.CMS.AC.UK@UKACRL
I would really appreciate useful routines for publication and
especially nice little tricks like the clear-screen routine for
turbo pascal which would be of benefit to users at this level.
27
Thanks for your attention - Bob Gowans.
Self Test Answers
a) Valid.
b) Valid
c) Valid
d) Invalid - there is a space character.
e) Invalid - program is a Pascal reserved word.
f) Invalid - does not start with a letter.
g) Invalid - Pascal identifiers do not allow a period.
28
Conclusion
Well, I have to say, I'm much happier with the second issue
of PNL. I'm glad I found the time to include some code examples.
I feel it is important to have something substantial for the
users to work with. I would especially like to thank Craig
Thurber and Bob Gowans for their help by including very well
written and useful articles. I hope that in the future they, and
others, will contribute more. It not only gives readers more than
one point of view in programming, but it also takes a big load
off of my shoulders.
I had originally planned an article on sorting routines for
this issue, but because of time constraints I've been finding it
very difficult to proceed. Instead of delaying the release of
this issue further, I have decided to go ahead and release this
issue and try to put the sorting article in a future issue.
I would be a liar if I said I think the code I have provided
is fool-proof. I've tested it, but I might have overlooked
something. If you do find a bug in the code I've provided, please
let me know and I will include code fixes in following issues.
My original plan was to have more than one issue of PNL out
a month, but unless I start getting a lot of article
contributions, that's going to be a difficult thing to
29
accomplish. I'll tell you one thing that would be really nice to
have is reviews written by users. If you would like to review
libraries and toolkits, feel free to send those reviews in. I am
also considering a column called 'Bits and Pieces' which will
have a bunch of small tips and techniques in pascal that are too
small to deserve articles by themselves, but which would be
useful.
Another column I would like to include is a reader mail
column for comments and Q & A.
I am developing a rather large distribution list and know I
will be racking up pretty hefty phone bills if it gets much
larger, so for the moment, here are the plans. I will only take a
few more people by node address on the distribution list. It's
much easier for me to send via BitNet, so I'll be taking BitNet
addresses until it gets too overbearing. If you have a mainframe
account that is on BitNet, you can pick it up from Simtel20
either by using either of the following:
TELL LISTSERV AT NDSUVM1 /PDGET PD:<MSDOS.PASCAL>PNLxxx.ZIP
or
TELL LISTSERV AT RPIECS /PDGET PD:<MSDOS.PASCAL>PNLxxx.ZIP
where xxx is the issue #. (These are CMS commands. If you're on a
Vax, the commands may differ slightly.) It is also available on
GEnie. I will start putting the FidoNet addresses, State, and
Area Code of people on the distribution list. Perhaps one of them
30
will be within local calling range of you.
What would be really nice, is if some people out there with
BitNet accounts in major cities would offer to receive a copy and
spread it around their cities for me. It's really difficult
getting a good distribution, but I'll work at it. Hopefully after
a while distribution will take care of itself. i.e. the PNL gets
popular enough that it gets spread around well.
Well, that just about does it for the second issue of PNL.
Hope it's been useful, and like I say and say and say, please
submit articles and send suggestions. This newsletter is for the
readers, not me.
_Pete Davis
31
The Pascal NewsLetter is Copyrighted by Peter Davis. It
may be freely distributed in un-modified form, but no
charge whatsoever may be incurred on the recipient.
The Pascal NewsLetter can be obtained from the
following locations:
GEnie : General Electric Network for Information
Exchange. It is located in the IBMPC filelist.
Simtel: Internet address: 26.2.0.74 or Simtel20.ARPA It
is located in the <MSDOS.PASCAL> directory.
Programmer's Forum : This is the home of the PNL. Each
issue can be found in the MAG
directory from the main area.
The number is on the title page.
If you would like to receive back issues of PNL
directly from me, send a diskette and $2.00 for
shipping. Don't forget to include your address.
Send your order to:
Peter Davis
4851 Brandywine St. NW
Washington, DC 20016
If you are a SysOp that will regularly carry PNL and
would like to have your bulletin board listed as such,
here, send me a message either by postal mail or at one
of the electronic addresses given on the title page,
with your bulletin board's name, phone number, your
name, maximum baud rate, and a description of up to 60
characters of your bbs.
32
Distribution List
The following is the phone numbers to bulletin boards known
to carry PNL. If you would like your bulletin board's name and
number added to or deleted from this list, please send me a
message at one of my many addresses.
The Programmer's Forum ................. Phone: (202) 966-3647
The Programmer's Forum is the home of the PNL.
The Bored .............................. Phone: (512) 303-0471
Classic City ........................... Phone: (404) 548-0726
Theive's World ......................... Phone: (713) 463-8053
Hippocampus ............................ Phone: (203) 484-4621
Rogers State College BBS ............... Phone: (918) 341-8982
The Foxtrot BBS ........................ Phone: (404) 793-2673
33
