
                     Chapter 14 - Example Programs


                             WHY THIS CHAPTER?

             Although  every  program  in this tutorial has  been  a
        complete  program,  each  one  has also been  a  very  small
        program intended to teach you some principle of  programming
        in  C.   It  would do you a disservice to leave you at  that
        point  without introducing you to a few larger  programs  to
        illustrate  how  to  put together the  constructs  you  have
        learned  to create a major program.   This chapter  contains
        four  programs  of increasing complexity,  each designed  to
        take  you  into a higher plateau of  programming,  and  each
        designed to be useful to you in some way.

             DOSEX will illustrate how to make DOS system calls  and
        will teach you,  through self-study, how the system responds
        to  the  keyboard.   WHATNEXT  reads commands input  on  the
        command line and will aid you in setting up a variable batch
        file,  one  that requests an operator input and responds  to
        the  input  by branching to a different part  of  the  batch
        file.

             LIST  is  the source code for the program you  used  to
        print  out the C source files when you began studying C with
        the aid of this tutorial.  Finally we come to VC, the Visual
        Calculator,  which  you should find to be a  useful  program
        even  if you don't study its source code.   VC uses most  of
        the  programming  techniques we have studied in this  course
        and  a few that we never even mentioned such  as  separately
        compiled subroutines.

             We  will  take a look at the example programs one at  a
        time  but  without  a complete explanation of  any  of  them
        because  you  have  been studying C for some  time  now  and
        should be able to read and understand most of these programs
        on  your  own.

                     DOSEX.C - The DOS Example Program

             The  copy of DOS that you received with your IBM-PC  or
        compatible has about 80 internal DOS calls that you can  use
        as  a programmer to control your peripheral devices and read
        information  or status from them.   Some of the earlier  IBM
        DOS manuals, DOS 2.0 and earlier, have these calls listed in
        the back of the manual along with how to use them.   Most of
        the  manuals  supplied  with compatible  computers  make  no
        mention  of  these  calls even  though  they  are  extremely
        useful.   These  calls  can  be  accessed  from  nearly  any
        programming  language but they do require some initial study
        to learn how to use them.   This program is intended to  aid
        you in this study.



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                     Chapter 14 - Example Programs


             Display the program on your monitor or print it out for
        reference.   It  is  merely a loop watching for  a  keyboard
        input or a change in the time.  If either happens, it reacts
        accordingly.   In line 32,  the function "kbhit()" returns a
        value  of 1 if a key has been hit but not yet read from  the
        input buffer by the program.

             Look at the function named "get_time" for an example of
        a  DOS call.   An interrupt 21(hex) is called after  setting
        the  AH  register to 2C(hex) =  44(decimal).   The  time  is
        returned in the CH,  CL, and DH registers.  Refer to the DOS
        call  definitions in your copy of DOS.   If the  definitions
        are  not included there,  Peter Nortons  book,  "Programmers
        Guide  to  the  IBM PC" is recommended as a  good  reference
        manual   for   these  calls  and  many   other   programming
        techniques.   Your compiler may have a built in function  to
        do this.  If you read your documentation, you will  probably
        find many useful functions available with your compiler that
        are  included  as  a convenience for you  by  your  compiler
        writer.

             Another useful function is the "pos_cursor()"  function
        that  positions the cursor anywhere on the monitor that  you
        desire  by  using  a  DOS  interrupt.   In  this  case,  the
        interrupt  used  is  10(hex) which is  the  general  monitor
        interrupt.  This particular service is number 2 of about  10
        different  monitor  services available.   This  function  is
        included here as another example to you.

             The  next  function,  service  number  6  of  interrupt
        10(hex)  is the window scroll service.   It should  be  self
        explanatory.

             In this program, the cursor is positioned and some data
        is  output  to the monitor,  then the cursor is "hidden"  by
        moving  it  to line 26 which is not  displayed.   After  you
        compile and run the program, you will notice that the cursor
        is  not  visible on the monitor.   This is possible  in  any
        program,  but  be  sure  to put the cursor  in  view  before
        returning  to  DOS  because  DOS does not  like  to  have  a
        "hidden" cursor and may do some strange things.

             Some time spent studying this program will be  valuable
        to  you as it will reveal how the keyboard data is input  to
        the  computer.   Especially of importance is how the special
        keys such as function keys, arrows, etc. are handled.   Also
        note that this program uses full prototype checking and is a
        good  example  of  how to use it.  Since it  also  uses  the
        "modern"  method  of  function definitions,  it  is  a  good
        example of that also.



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                     Chapter 14 - Example Programs



                  WHATNEXT.C - The Batch File Interrogator

             This  is  an  example of how to read the  data  on  the
        command line following the function call.  Notice that there
        are  two variables listed within the  parentheses  following
        the main() call.   The first variable is a count of words in
        the entire command line including the command itself and the
        second  variable  is  a  pointer to  an  array  of  pointers
        defining the actual words on the command line.

             First the question on the command line, made up of some
        number of words, is displayed on the monitor and the program
        waits for the operator to hit a key.   If the key hit is one
        of  those  in the last "word" of the group of words  on  the
        command  line,  the number of the character within the group
        is  returned to the program where it can be tested with  the
        "errorlevel" command in the batch file.   You could use this
        technique  to  create a variable AUTOEXEC.BAT  file  or  any
        other  batch  file  can  use this for  a  many  way  branch.
        Compile  and  run this file with TEST.BAT for an example  of
        how  it  works in practice.   You may  find  this  technique
        useful  in  one  of  your batch files and  you  will  almost
        certainly  need  to  read in  the  command  line  parameters
        someday.

             An  interesting alternative would be for you to write a
        program  named "WOULD.C" that would return a 1 if a  "Y"  or
        "y"  were typed and a zero if any other key were hit.   Then
        your batch file could have a line such as;

        WOULD YOU LIKE TO USE THE ALTERNATIVE METHOD (Y/N)

             Dos would use "WOULD" as the program name,  ignore  the
        rest  of  the  statement  except for displaying  it  on  the
        screen.   You  would  then respond to the  question  on  the
        monitor  with a single keyhit.   Your batch file would  then
        respond   to  the  1  or  0  returned  and  either  run  the
        alternative  part  of  the batch file or  the  primary  part
        whatever each part was.

        WOULD YOU LIKE PRIMARY (Y/N)
        IF ERRORLEVEL 1 GOTO PRIMARY
        (secondary commands)
        GOTO DONE
        :PRIMARY
        (primary commands)
        :DONE





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                     Chapter 14 - Example Programs



                        LIST.C - The Program Lister

             This program is actually composed of two files,  LIST.C
        and  LISTF.C  that must be separately  compiled  and  linked
        together  with your linker.   There is nothing new here  and
        you  should  have  no  trouble compiling  and  linking  this
        program  by  reading the documentation  supplied  with  your
        C compiler.

             The  only  thing  that is new in this  program  is  the
        inclusion   of  three  "extern"  variables  in  the  LISTF.C
        listing.   The only purpose for this is to tie these  global
        variables  to  the main program and tell the  compiler  that
        these  are not new variables.   The compiler will  therefore
        not  generate any new storage space for them but simply  use
        their names during the compile process.   At link time,  the
        linker  will  get  their actual storage locations  from  the
        LIST.OBJ  file and use those locations for the variables  in
        the  LISTF part of the memory map also.   The  variables  of
        those  names in both files are therefore the same  identical
        variables and can be used just as any other global variables
        could be used if both parts of the program were in one file.

             There is no reason why the variables couldn't have been
        defined  in the LISTF.C part of the program and declared  as
        "extern"  in the LIST.C part.   Some of the variables  could
        have  been  defined  in one and some in the  other.   It  is
        merely a matter of personal taste.   Carried to an  extreme,
        all of the variables could have been defined in a third file
        and  named "extern" in both of these files.   The third file
        would then be compiled and included in the linking process.

             It would be to your advantage to compile, link, and run
        this  program to prepare you for the next program  which  is
        composed of 6 separate files which must all work together.

                        VC.C - The Visual Calculator

             This  program  finally ties nearly everything  together
        because  it uses nearly every concept covered in the  entire
        tutorial.   It  is so big that I will not even try to  cover
        the finer points of its operation.   Only a few of the  more
        important points will be discussed.

             The  first  thing  you  should do  is  go  through  the
        tutorial  for  VC included in the file  VC.DOC.   There  are
        several  dozen  steps  for you to execute,  with  each  step
        illustrating some aspect of the Visual Calculator.  You will
        get  a  good feel for what it is capable of doing  and  make
        your study of the source code very profitable.  In addition,


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                     Chapter 14 - Example Programs


        you  will  probably  find  many  ways  to  use  the   Visual
        Calculator  to  solve problems involving calculations  where
        the  simplicity  of  the problem at hand  does  not  warrant
        writing a program.

             Notice that the structure definitions,  used in all  of
        the  separate parts of the program,  are defined in the file
        STRUCT.DEF.   During  program development,  when  it  became
        necessary  to change one of the structures slightly,  it was
        not  necessary to change it in all of the  files,  only  one
        file  required modification which was then "included" in the
        source files.   Notice that the transcript data is stored in
        a doubly linked list with the data itself being stored in  a
        separate  dynamically allocated char string.   This line  is
        pointed to by the pointer "lineloc".

             For  ease  of development,  the similar functions  were
        grouped together and compiled separately.   Thus, all of the
        functions  involving the monitor were included in  the  file
        named  VIDEO.C,  and all of the functions involving the data
        storage were grouped into the FILE.C  collection.   Dividing
        your  program  in  a  way similar to  this  should  simplify
        debugging and future modifications.

             Of special interest is the "monitor()" function.   This
        function  examines  the  video mode through  use  of  a  DOS
        command  and  if it is a 7,  it assumes it is  a  monochrome
        monitor,  otherwise it assumes a color monitor.   The colors
        of  the various fields are established at this time and used
        throughout  the  program.   Most  of  the  data  is  written
        directly  to the video memory,  but some is written  through
        the standard BIOS routines.

             The file DEFIN.H is a catalogue of the functions to aid
        in finding the functions.  This file was generated as one of
        the  first  files  and was maintained and  updated  for  use
        during  the  entire  design and coding  lifetime.   It  also
        contains all of the prototype definitions for the  functions
        in  all  of  the source files, and is  "included"  in  every
        source file to do prototype checking.













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