Getting started in Turbo C

 

                   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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                   Chapter 2 - Getting started in Turbo C

                      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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                   Chapter 2 - Getting started in Turbo C

        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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