C Programming for Absolute Beginners


			    Author: Joseph Bouhabib


   Ed: At the last minute, Joe has asked me to note that all the example 
  programs in this drawer run fine and compile fine with the PDC compiler
  from Fish 351 (found also on our C programming 5-pack).

   By coincidence we have two series of C for Beginners running this issue,
  one by Jason Lowe and this by Joe - each takes a different tack, so check
  them both out.


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				CHAPTER THREE

   Sorry about the delay in getting this article out. I was so upset at Tim
  Strachan's description of me in the last article I couldn't think straight.
  I AM NOT a lawyer who'd rather be a programmer, I'm a lawyer who'd rather
  be an idle billionaire with plenty of free time to program. The defamation
  writ is on its way MR EDITOR.

   From the response I have had to my first two articles, I can draw the
  following conclusions:

   1.Those of you who are trying to learn C Programming used PDC.

   2.Those that are trying to use PDC have had very little success.

   3. I have not used PDC before.

   From next time, I will make sure that any examples I give work both with
  DICE (Matt Dillon's shareware C environment) and PDC.  As I mentioned in my
  second article, I will get straight into C Programming as we haven't
  actually done anything in the first two articles.  Firstly however, I would
  like to correct some of the mistakes in the first two articles. The major
  one is that the example of the source code which I gave was incorrectly set
  out.  It should have read as follows:

/* first easy program */

#include <stdio.h>
main()
{
printf ("Hello World!\n");
}


   Further more, please ignore any thing after the words "Character Strings"
  in my first article as these were copied from someone else's work and I
  haven't bothered to make them understandable.

   The other thing I would like to mention is that in my second article I
  listed a program which is related to CROBOTS. Although in my second
  article I said that I would explain what this meant, I think that I will
  leave that for the time being, as the information contained in this article
  should cover all aspects of that program.

   Use a Text editor

   The most important mistake (for those of you who may not realise the
  difference) is that NOT ALL WORDPROCESSORS can be used to write source
  code. For Dice or any other C compiler to work, it must be able to save
  the source code in ASCII format (i.e. without any formatting controls that
  are specific to the wordprocessor or the Amiga). Most wordprocessors have
  this capability but it's safer to use a text editor.

   What I hope to do by the end of this article is have you actually compile
  a useful (my interpretation of useful, not yours) program.

   Firstly, I will go through the procedure to install Dice onto a hard disk
  system.  As I have a harddrive, this was quite easy to do using the hard
  disk installing program which comes with the registered version of Dice.
  When that program is run, it asks for a destination directory. I followed
  the onscreen prompts for inserting the three disks that came with the
  registered version of Dice, as requested.

   NOTE: The whole thing takes about two and half megabytes to install
  properly.

   CAUTION: Make sure (whether or not using a hard drive or floppy disk
  system) that your system is properly and fully backed up.  The first time I
  installed the system I had a lot of problems, especially with my mountlist.
  After the files are copied over, the installation program will attempt to
  amend your startup-sequence.

   It will also replace your mountlist with an entry which will drastically
  affect the way your system operates.  In fact, my original mountlist was
  1749 bytes long, and this was replaced with a mountlist which was only 80
  bytes long.  I found this out the hard way.  So long as your mountlist
  contains a null entry as follows:

null:      Handler = L:null-handler
	   Stacksize = 500
	   Priority = 5
      GlobVec = 1
#

   Then after installation is complete you should delete the mountlist which
  Dice installs and restore your own mountlist amended accordingly, to
  include the above lines.

   You then need to add the following line to your start upsequence:

Execute SYS:S/Startup-sequence.DICE

   Dice will actually save your original startup-sequence, but will add
  `startup-sequence.Dice' to the S: directory.  You then need to amend
  `startup-sequence.Dice' to include at least the following line, which for
  some reason is not included in the installation program.  You will have to
  add DCC:BIN to your path. Do this by inserting the line:

path add DCC:BIN

   Also, at the end of `startup-sequence.Dice' you should add the following
  line:

Setenv DCCOPTS -1.3.

   Of course, if you are using WB2.0 you should change 1.3 to 2.0.



THE COMPONENTS OF A PROGRAM

   All C programs share certain basic components and characteristics. All C
  programs consist of one or more functions, each of which contains one or
  more statements.  In C, a function is a named subroutine that can be called
  by other parts of the program. Functions are the building blocks of C. A
  statement specifies an action to be performed by the program i.e.statements
  are the parts of your program that actually perform operations.  Statements
  are contained within functions.

   All C statements end with a semicolon. C does not recognize the end of
  the line as a terminator.  This means there are no constraints on the
  position of statements within a line.  Also, you may place two or more
  statements on one line.

   The simplest form of a C function is shown here.

function-name ()
{
	statement sequence;
}


   Where function-name is the name of the function and the statement sequence
  may be one or more statements. Technically, a function can contain no
  statements, but obviously, this means it wouldn't be able to do anything.
  There are a number of limitations on what you can call a function. It must
  be comprised of only the upper- and lowercase letters of the alphabet, the
  digits 0-9, and the underscore (_).  C is case-sensitive, which means that
  as "function" and "Function" are two different names.

   Main ()

   A C program must have a function called "main ()".  This is the function
  at which execution of your program begins.  When your program begins
  running, it starts executing the statements inside the main () function,
  beginning with the first statement after the opening curly brace and ending
  when the closing curly brace is reached.  The actual curly brace only
  exists in the source code and does not exist in the compiled version of
  your program, but it is helpful to think of it in this way.

   Library Functions

   Another important component of all C programs is library functions. All C
  compilers supply a set of library functions which your program may use.
  This collection of functions is usually referred to as the C standard
  library.  This concept will be discussed in detail later. However, before
  I go on, one of the most common library functions is called printf(). This
  function is included in the example at the beginning of this article. It
  is C's general purpose output function.  Although printf() is quite
  versatile, its simplest form is

printf("string-to-output");

   The printf() function outputs the characters that are contained between
  the beginning and ending double quotes to the screen. The double quotes
  themselves are not displayed on the screen.  In C, one or more characters
  enclosed between double quotes is called a string.  The quoted string
  between printf ()'s parentheses is said to be an argument to printf().  In
  general, information passed to a function is called an argument.  In C,
  calling a library function is a statement; therefore, it must end with a
  semicolon.

   To Call a function

   To call a function, you specify its name followed by a parenthesized list
  of arguments that you will be passing to it. If the function does not
  require any arguments, the parenthesized list will be empty.  If there is
  more than one argument, the arguments must be separated by commas.

   The header file

   Another component common to most C programs is the header file.  In C,
  information about the standard library functions is found in various files
  supplied with your compiler.  The files all end with a .H extension.  The C
  compiler uses the information in these files to handle the library
  functions properly.  The "#include" directive, which again is present in
  our example above tells the compiler to read in another file and include it
  with your program.  Again this is a topic to be dealt in detail later.

   The most commonly required header file is called STDIO.H. The directive

#include "stdio.h"

   will include the STDIO.H file in your program.

   You can specify the file name in either upper-or lower case, but lowercase
  is the traditional method.  The STDIO.H header file contains, inter alia,
  information related to the printf() library function.  The #include
  directive does not end with a semicolon because it is not a C keyword that
  can define a statement.  Instead, it is an instruction to the C compiler
  itself.

Examples:

   Included with this article should be the following files:

1. hello.c
2. hello
3. another.c
4. another
5. faren.c
6. faren

   When you click on the icons for the files with .c extensions, all you will
  see is the source code. The other programs are the compiled versions.

   Compiling hello.c with DICE

   The first file, hello.c is the the program listed at the beginning of this
  article. It is in a form ready to compile. To try it with Dice, type at
  the Shell prompt:

dcc hello.c -0 hello

   NOTE: This is assuming tha you have set up Dice correctly. This program
  is so simple it should compile with any c compiler you are using.

   The second file, hello is the actual compiled version. To see what it
  does, type from the Shell:

hello

   Not very earth shattering is it? Still, we're only beginners. We'll look
  at something a little more interesting in a minute. But first, if you look
  at the source code, even though it is only six lines long, it illustrates
  those aspects common to all C programs.  Let's examine it line by line.
  The first line is a comment which does not affect the source or the
  compiled program.

   The second line of the program is

#include "stdio.h"

   It causes the file STDIO.H to be read by the C compiler and to be included
  with the program.  This file contains information related to printf().

   The second line,

main ()

   begins the main () function which all C programs must have. This is where
  program execution begins.

   After main () is an opening curly brace which marks the beginning of
  statements that make up the function.

   The next line in the program is

printf ("Hello world!\n");

   This is a C statement.  It calls the standard library function, printf(),
  which causes the string to be displayed. The \n makes the program go to a
  new line. The program ends when the closing curly brace is encountered.

   The file another.c is just a tiny bit more interesting than hello.c. Run
  it to see what it does. If you think it's totally useless, how about
  changing it and running your own message from the startup-sequence.

   The point about another.c is that statements are executed in order
  beginning with the opening curly brace and ending with the closing curly
  brace.

   The program Faren

   Now let's try something a little more interesting and useful. The fifth
  program included will print out a table of Fahrenheit temperatures and
  their Celsius (approximately) equivalents. The formula is:

C = (5/9)(F-32)

   Look at the source code provided. The line

int lower, upper, step, fahr, celsius;

  contains variables. These will be the main subject of the next article.
  In C, all variables must be declared before they are used, usually at the
  beginning of the function in which they are used and before any statements.
  A declaration consists of a ~type" and a list of variables which have that
  type. In the above line, the ~int' stands for integers (ie whole numbers).
  the variables are pretty self explanatory, don't you think?

   The lines

lower = 0;
upper = 300;
step = 20;
fahr = lower;

  set the variables to their starting values. Note the semicolon ending
  each statement. The next line contains the `while" statement and its
  condition.  The argument tests the condition in the parenthesis and if
  true, the statements in the curly braces are executed.

   I'll leave the rest of the explanation for now, because you should now be
  able to change this program to print a Celsius to Fahrenheit table. You
  should also be able to "write" your own program to change other Imperial
  units to their metric equivalents.


      Good luck! It's really not all that hard.

   PS The compiled programs hello and faren I've included run OK from the
  Shell, but for some reason give an error message when run with IconX. I
  haven't figured out why yet.  Another runs OK. (Ed: see the reasons next
  issue.)

Joseph Bouhabib
10 Jennings Avenue
Bass Hill 2197


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