
                   Chapter 2 - Getting started in Turbo C


                            YOUR FIRST C PROGRAM

             The  best way to get started with C is to actually look
        at  a  program, so load the file named  TRIVIAL.C  with  the
        Integrated Environment for display on the monitor.  You  are
        looking at the simplest possible C program.  There is no way
        to   simplify  this  program  or  to  leave  anything   out.
        Unfortunately, the program doesn't do anything.

             The  word  "main" is very important,  and  must  appear
        once,  and only once in every C program.   This is the point
        where execution is begun when the program is run.   We  will
        see  later that this does not have to be the first statement
        in  the  program  but  it must exist  as  the  entry  point.
        Following  the "main" program name is a pair of  parentheses
        which  are  an  indication to the compiler that  this  is  a
        function.   We will cover exactly what a function is in  due
        time.   For now,  I suggest that you simply include the pair
        of parentheses.

             The  two curly brackets,  properly called  braces,  are
        used to define the limits of the program itself.  The actual
        program  statements  go between the two braces and  in  this
        case,  there  are  no  statements because the  program  does
        absolutely nothing.  You can compile and run this program by
        hitting Alt-R if in the Integrated Environment, but since it
        has no executable statements, it does nothing.  Keep in mind
        however, that it is a valid C program.

                       A PROGRAM THAT DOES SOMETHING

             For  a much more interesting program,  load the program
        named WRTSOME.C and display it on your monitor.   It is  the
        same  as  the  previous  program  except  that  it  has  one
        executable statement between the braces.

             The  executable  statement  is a  call  to  a  function
        supplied as a part of your Turbo C library.  Once again,  we
        will not worry about what a function is, but only how to use
        this  one  named "printf".  In order to output text  to  the
        monitor,  it  is  put within the  function  parentheses  and
        bounded by quotation marks.  The end result is that whatever
        is included between the quotation marks will be displayed on
        the monitor when the program is run.

             Notice the semi-colon at the end of the line.  C uses a
        semi-colon as a statement terminator,  so the semi-colon  is
        required  as  a  signal to the compiler that  this  line  is
        complete.   This  program  is also executable,  so  you  can
        compile  and  run  it to see if it does what  you  think  it
        should.


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                      ANOTHER PROGRAM WITH MORE OUTPUT

             Load  the  program  WRTMORE.C and display  it  on  your
        monitor  for an example of more output and another small but
        important concept.  You will see that there are four program
        statements  in  this program, each one being a call  to  the
        function  "printf".   The top line will be  executed  first,
        then the next, and so on, until the fourth line is complete.
        The statements are executed in order from top to bottom.

             Notice  the funny character near the end of  the  first
        line,  namely  the backslash.   The backslash is used in the
        printf   statement  to  indicate  that  a  special   control
        character  is  following.  In this case, the  "n"  indicates
        that  a  "newline" is requested.  This is an  indication  to
        return  the cursor to the left side of the monitor and  move
        down  one  line.  It is commonly referred to as  a  carriage
        return/line  feed.  Any place within text that  you  desire,
        you  can put a newline character and start a new line.   You
        could even put it in the middle of a word and split the word
        between two lines.  The C compiler considers the combination
        of the backslash and letter n as one character.

             A complete description of this program is now possible.
        The  first  printf outputs a line of text  and  returns  the
        carriage.   The  second printf outputs a line but  does  not
        return  the carriage so that the third line is  appended  to
        the second, then followed by two carriage returns, resulting
        in a blank line.  Finally the fourth "printf" outputs a line
        followed by a carriage return and the program is complete.

             Compile and run this program to see if it does what you
        expect  it to do.   It would be a good idea at this time for
        you to experiment by adding additional lines of printout  to
        see if you understand how the statements really work.

                          LETS PRINT SOME NUMBERS

             Load  the  file named ONEINT.C and display  it  on  the
        monitor for our first example of how to work with data in  a
        C program.  The entry point "main" should be clear to you by
        now as well as the beginning brace.  The first new thing  we
        encounter is the line containing "int index;", which is used
        to define an integer variable named "index".  The "int" is a
        reserved  word  in  C, and can therefore  not  be  used  for
        anything else.  It defines a variable that can have a  value
        from  -32768  to  32767  in Turbo C, and  in  most  other  C
        compilers  for microcomputers.  The variable name,  "index",
        can be any name that follows the rules for an identifier and


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        is  not one of the reserved words for Turbo C. The  Turbo  C
        User's Guide has a list of reserved words on page 199.   The
        final  character  on  the  line,  the  semi-colon,  is   the
        statement terminator used in C.

             Note  that, even though we have defined a variable,  we
        have not yet assigned a value to it.  We will see in a later
        chapter  that additional integers could also be  defined  on
        the  same  line,  but we will  not  complicate  the  present
        situation.

             Observing the main body of the program, you will notice
        that  there are three statements that assign a value to  the
        variable  "index",  but only one at a time.   The first  one
        assigns the value of 13 to "index", and its value is printed
        out.   (We will see how shortly.)  Later, the value of 27 is
        assigned to "index",  and finally 10 is assigned to it, each
        value  being  printed out.   It should be intuitively  clear
        that  "index"  is  indeed  a variable  and  can  store  many
        different  values.   Please note that many times  the  words
        "printed  out" are used to mean "displayed on the  monitor".
        You  will  find that in many cases  experienced  programmers
        take  this  liberty,  probably due to the "printf"  function
        being used for monitor display.

                          HOW DO WE PRINT NUMBERS

             To  keep  our promise,  let's return  to  the  "printf"
        statements  for a definition of how they work.   Notice that
        they are all identical and that they all begin just like the
        "printf"  statements  we  have  seen  before.    The   first
        difference occurs when we come to the % character.   This is
        a  special character that signals the output routine to stop
        copying characters to the output and do something different,
        namely output a variable.   The % sign is used to signal the
        output  of  many different types of variables, but  we  will
        restrict  ourselves  to  only one  for  this  example.   The
        character  following the % sign is a "d", which signals  the
        output routine to get a decimal value and output it.   Where
        the decimal value comes from will be covered shortly.  After
        the  "d",  we  find the familiar \n, which is  a  signal  to
        return the video "carriage", and the closing quotation mark.

             All  of  the  characters between  the  quotation  marks
        define  the pattern of data to be output by this  statement,
        and  after  the pattern,  there is a comma followed  by  the
        variable name "index".  This is where the "printf" statement
        gets  the decimal value which it will output because of  the
        "%d"  we saw earlier.   We could add more "%d" output  field
        descriptors within the brackets and more variables following
        the  description  to cause more data to be printed with  one


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                   Chapter 2 - Getting started in Turbo C


        statement.   Keep in mind however, that it is important that
        the  number of field descriptors and the number of  variable
        definitions must be the same or the runtime system will  get
        confused and probably quit with a runtime error.

             Much  more  will  be  covered at a later  time  on  all
        aspects  of input and output formatting.  A reasonably  good
        grasp  of  these  fundamentals are  necessary  in  order  to
        understand  the following lessons.  It is not  necessary  to
        understand everything about output formatting at this  time,
        only a fair understanding of the basics.

             Compile and run ONEINT.C and observe the output.

                        HOW DO WE ADD COMMENTS IN C

             Load the file COMMENTS.C and observe it on your monitor
        for an example of how comments can be added to a C  program.
        Comments  are  added to make a program more readable to  you
        but the compiler must ignore the comments.   The slash  star
        combination  is used in C for comment delimiters.   They are
        illustrated  in the program at hand.   Please note that  the
        program does not illustrate good commenting practice, but is
        intended  to illustrate where comments can go in a  program.
        It is a very sloppy looking program.

             The  first slash star combination introduces the  first
        comment  and  the star slash at the end of  the  first  line
        terminates this comment.  Note that this comment is prior to
        the beginning of the program illustrating that a comment can
        precede the program itself.  Good programming practice would
        include  a  comment  prior  to  the  program  with  a  short
        introductory  description of the program.   The next comment
        is  after the "main()" program entry point and prior to  the
        opening brace for the program code itself.

             The  third  comment starts after the  first  executable
        statement and continues for four lines.   This is  perfectly
        legal  because  a comment can continue for as many lines  as
        desired  until  it is terminated.   Note carefully  that  if
        anything  were included in the blank spaces to the  left  of
        the  three  continuation lines of the comment,  it would  be
        part  of the comment and would not be  compiled.   The  last
        comment  is located following the completion of the program,
        illustrating  that  comments can go nearly anywhere in  a  C
        program.

             Experiment  with  this program by  adding  comments  in
        other places to see what will happen. Comment out one of the
        printf  statements by putting comment delimiters both before
        and after it and see that it does not get printed out.


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                   Chapter 2 - Getting started in Turbo C



             Comments are very important in any programming language
        because  you will soon forget what you did and why  you  did
        it.   It  will  be  much  easier to modify  or  fix  a  well
        commented  program  a year from now than one with few or  no
        comments.   You will very quickly develop your own  personal
        style of commenting.

             The Turbo C compiler will allow you to "nest"  comments
        which  can  be  very handy if you need to  "comment  out"  a
        section  of  code  during  debugging.   In  order  to   nest
        comments, you must make a change in the default by selecting
        the  "Options"  menu, followed by the "Compiler"  menu,  and
        finally the "Source" menu.  The default for nested  comments
        is off, but changing it will not affect any of the files  in
        this tutorial.

                           GOOD FORMATTING STYLE

             Load  the  file  GOODFORM.C  and  observe  it  on  your
        monitor.   It  is  an example of a well  formatted  program.
        Even though it is very short and therefore does very little,
        it  is very easy to see at a glance what it does.   With the
        experience  you have already gained in  this  tutorial,  you
        should  be  able  to very quickly grasp the meaning  of  the
        program in it's entirety.  Your C compiler ignores all extra
        spaces  and  all carriage returns  giving  you  considerable
        freedom  concerning how you format your program.   Indenting
        and  adding spaces is entirely up to you and is a matter  of
        personal  taste.   Compile and run the program to see if  it
        does what you expect it to do.

             Now load and display the program UGLYFORM.C and observe
        it.   How  long  will it take you to figure  out  what  this
        program  will do?   It doesn't matter to the compiler  which
        format style you use, but it will matter to you when you try
        to  debug  your program.   Compile this program and run  it.
        You may be surprised to find that it is the same program  as
        the  last  one,  except for the formatting.   Don't get  too
        worried about formatting style yet.  You will have plenty of
        time  to  develop  a  style of your own  as  you  learn  the
        language.   Be observant of styles as you see C programs  in
        magazines, books, and other publications.

             This  should  pretty well cover the basic  concepts  of
        programming  in  C,  but as there are many other  things  to
        learn, we will forge ahead to additional program structure.






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                   Chapter 2 - Getting started in Turbo C


        PROGRAMMING EXERCISES

        1. Write a program to display your name on the monitor.

        2. Modify  the  program to display your address  and  phone
           number  on  separate  lines  by  adding  two  additional
           "printf" statements.














































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