Chapter 9

                                              EXAMPLE PROGRAMS



WHY THIS CHAPTER?
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The programs included in this chapter are intended to be
illustrations to you in how to write a complete program.  The
programs are meant to be useful to you either as an example
of how to do some operation or as utility programs for your
own personal use.


TIMEDATE - Get Time and Date
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This program calls one of the DOS             ================
functions to get the current time and           TIMEDATE.MOD
date.  The various components of the time     ================
and date are input as variables and can be
printed or displayed in any format you desire.  Your
particular compiler may use a different format because there
is no standard in Modula-2.  This is one of those areas that
will probably deviate from compiler to compiler.  If you study
your documentation that came with your compiler, you will find
many other calls of this type described.  This program is
meant to be an illustration of how to use this particular
call.  Note that this program is especially written to use the
MS-DOS calls available on an IBM-PC microcomputer and will
probably have no resemblance to the calls on some other
system.


AREAS - Calculate Areas
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This program is presented as an                ===============
illustration of how to build up a larger          AREAS.MOD
program than any we have examined up to        ===============
this point.  Notice that the main program
is simply one CASE statement that calls all of the other
procedures.  It would be very simple to include the code from
each procedure right in the CASE statement and have no
procedure calls, but it would make the program a little more
difficult to understand.  The way this example is formatted,
the code is very easy to understand.  After you understand the
main program, it is a simple matter to visit each procedure
to see exactly what they do.

Observe carefully how the menu works in this program.  It
reads one keystroke and responds immediately making it a very
simple program to use.

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                                  Chapter 9 - Example Programs

PC - Printer Control
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This is a very useful program that you can    ================
use to control your printer.  It is                PC.MOD
specifically set up for an Epson RX-80,       ================
but you can modify the control characters
to set up your printer to whatever mode you desire.  To use
it, you call the program by typing its name on the DOS command
line, and supply a single letter according to the displayed
menu.  The program will send the requested control sequences
to the printer to select the enhanced, compressed, or whatever
mode you desire.  If your printer is located physically remote
from you, you can use this program to send a formfeed to the
printer by selecting the F option.  If you have some longer
control sequences to send, you may want to store the values
in a string and use a loop to output the data until you come
to an 0C character.



LIST - List Program File
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If you ran the batch file named LISTALL as    ================
suggested at the beginning of this                LIST.MOD
tutorial to print out all of the source       ================
files, you have already used a program
similar to this one.  This program will list any ASCII file,
adding line numbers, page numbers, and the date and time, on
the printer.  It is specifically designed to be a program
listing utility.  The operation is very simple, and you should
have no trouble in understanding this program or what it does.

Feel free to modify this program for your own personal use.

The LIST.EXE file on the distribution disk is not a result of
compiling this source file but was written and compiled in
TURBO Pascal.  This was done in order to alleviate the
possibility of any legal problem, because Borland
International does not require a distribution fee or a run-
time license for compiled programs.  The Modula-2 program is
nearly identical to the distributed executable program, and
allows you to modify the source code to meet your own personal
needs.

Additional programs will be given at the end of Part III for
your information.  You will no doubt find additional example
programs in various books and periodicals and it would be to
your advantage to spend some time studying them as
illustrations of both good and bad practices.



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                                  Chapter 9 - Example Programs

PROGRAMMING EXERCISE
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1.   Study the source code for LIST.EXE for a period of time,
     then compile it with your compiler.  You may need a few
     modifications to get it to compile properly because all
     Modula-2 compilers are not identical.  After successfully
     compiling and executing this program, put it aside.
     Starting with a blank sheet of paper, write and debug
     your own version of a program lister.  This is a fairly
     major programming assignment, but if you get stuck, you
     have the existing program to help you over the rough
     spots.  If you complete this assignment, you will have
     gained a good bit of experience in writing Modula-2, and
     you will have your own customized program lister that you
     thoroughly understand.





































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