Introduction on C

1
Introduction on C

• C is a high-level programming language that forms
  the basis to
• other programming languages such as C, Perl and
  Java. It
• was developed by a guy called Dennis Ritchie in
  1972. He
• named it C because there was an existing
  programming
• language called B.
• You should also get a C compiler and write and
  test your own
• programs I learnt best from my (many) careless
  mistakes.
• There are many free compilers available on the
  net. For
• freeware, shareware and demo programs, try
  performing a
• search at http//download.cnet.com. So why
  should you learn
• C? Well, because it opens the doors to other
  languages like C, Java .

2
Syntax

• The C code you write is called the SYNTAX.
• Syntax is a mixture of
• C keywords like int, for and return.
•  Constants and variable.
• Operators like
• (arithmetic "addition"),
• (logical "or") and
• (the "address of" operator).
• Note that C is CASE SENSITIVE!
• White space in a C program does not affect.
• Use extra spaces to make your programs more
  readable

3
Compilers

• Microsoft's Visual C 6.0 (Room 106 209) This
  is a
• powerful package and is suitable for people who
  are
• interested in software engineering. In general,
  C packages
• are fine for compiling C programs the compiler
  executed
• depends on the extension of your source file(s).
• UNIX-based compiler (gcc available on laplace ).
• The command for compiling is of the form
• gcc world.c -o world .
• The filename after cc is the file to be compiled,
  which is
• "world.c" in this case, the filename after -o is
  the output file,
• which is "world". The output filename is the word
  you type to
• run the program.

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Commenting Your Code

• You can add comments to your code by enclosing
  your
• remarks within /and /. However, nested comments
  aren't
• allowed
• A few properties of comments    
• They can be used to inform the person viewing
  the code what the code does. This is helpful when
  you revisit the code at a later date.   
• The compiler ignores all the comments.
  Hence, commenting does not affect the efficiency
  of the program.   
• You can use / and / to comment out sections of
  code when it comes to finding errors, instead of
  deletion

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Examples

• / Comments spanning several /
• / lines can be commented/
• / out like this!/
• / But this is a simpler way of doing it! /
• // These are C
• / / NESTED COMMENTS ARE ILLEGAL!! /

6
Creating Executable Programs

• There are several tasks that need to be performed
  before you
• can run a program coding, compiling and linking.
• 1.  You have to write the source code in C. You
  declare which
• header files you want to include within the
  source code. The
• source code must be saved with the extension .c
• 2.  Then you run the compiler, which translates
  the source code into machine, or binary code,
  which the computer can understand. Computers do
  NOT understand C !
• 3.  Sometimes the source code is still lacking
  some parts, so after going through the compiler,
  the code is passed through a LINKER. This
  basically "links" the source code to other
  library or object files so that the final binary
  code is produced.

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Hello World
Your First Program include ltstdio.hgt int
main() printf("Hello World!\n")
return 0

• The include Directive
• Header Files
• Header files have the extension .h
• and the full filename follows from
• The include directive.

8
The main Function

• A FUNCTION can be thought of a set of
  instructions that is carried out when it is
  CALLED.
• All C programs must have a main function. You can
  only have one, but you can place it anywhere
  within the code.
• The program always start with the main function
  and ends when the end of main is reached.
  Functions return a value too - this will be
  explained later.
• If a function returns nothing, it's return type
  is of type void
• The main function is special, as it returns an
  integer by default, which is why you'll see me
  write return 0.

9
Constants and Variables

• Variables are like containers in your computer's
  memory - you can store values in them and
  retrieve or modify them when necessary.
• Constants are like variables, but once a valued
  is stored (i.e. the constant is INITIALIZED),
  its value cannot be change
• There are several rules that you must follow when
  naming variables

10
Do no forget

• Variable names....
• CANNOT start with a number
  2times
• CAN contain a number elsewhere
  times2
• CANNOT contain any arithmetic operators...
  abc
• ... or any other pun ctuation marks...
  _at_!!
• ... but may contain or begin with an underscore
  _height
• CANNOT be a C keyword
  while
• CANNOT contain a space
  stupid me
• CAN be of mixed cases
  HaykMelik

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Some Terminology

• EXPRESSIONS consist of a mixture of constants,
  variables and operators (more about operators
  later). They return values.
• 17 / a constant /
• x / a variable /
• x 17 / a variable plus a constant /
• STATEMENTS are instructions and are terminated
  with a semicolon,.
• x 1 8
• printf("We will learn printf soon!\n")
• int x, y, z / more on "int"
  later /
• STATEMENT BLOCKS, on the other hand, can contain
  a group of statements

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Example

• STATEMENT BLOCKS, on the other hand, can contain
  a
• group of statements
• if(x10) / block 1 /
• printf("x equals 10\n")
• x 11 printf("Now x equals
  11\n")
• x x 1 printf("Now x equals
  12\n")
• 
  / end of block 1 /
• else / block 2 /
• printf("x not equal to 10\n")
• printf("Good bye!\n")
• / end of block 2 /

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Types of Constants

• Numbers are considered as LITERAL constants
• you can't change the number 20, nor can you
  assign something
• else into 20.
• On the other hand, SYMBOLIC constants can be
  assigned a
• value during initialization and are represented
  by a word.
• const int radius 5
• There are several ways to define constants in C.
  Later, we will meet the define directive and the
  enum keyword
• two more ways of defining constants.

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HW 4

• Readig
• LAB
• Homework
• Assigned Due 09/23/02
• PS. To submit you have to use the fallowing
  command
• mail melikianlt typescript

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Life Cycle
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input
18
compiler