C PROGRAMMING

Introduction to C
Programming
Introduction

Books
“The Waite Group’s Turbo C Programming for PC”,
Robert Lafore, SAMS
“C How to Program”, H.M. Deitel, P.J. Deitel,
Prentice Hall

What is C?
C
A language written by Brian Kernighan
and Dennis Ritchie. This was to be the
language that UNIX was written in to
become the first "portable" language
In recent years C has been used as a general-
purpose language because of its popularity with
programmers.

Why use C?
Mainly because it produces code that runs nearly as fast
as code written in assembly language. Some examples
of the use of C might be:
– Operating Systems
– Language Compilers
– Assemblers
– Text Editors
– Print Spoolers
– Network Drivers
– Modern Programs
– Data Bases
– Language Interpreters
– Utilities
Mainly because of the portability that writing standard C programs can
offer

History
In 1972 Dennis Ritchie at Bell Labs writes C and in
1978 the publication of The C Programming Language
by Kernighan & Ritchie caused a revolution in the
computing world
In 1983, the American National Standards Institute
(ANSI) established a committee to provide a modern,
comprehensive definition of C. The resulting definition,
the ANSI standard, or "ANSI C", was completed late
1988.

Why C Still Useful?
C provides:
Efficiency, high performance and high quality s/ws
flexibility and power
many high-level and low-level operations  middle level
Stability and small size code
Provide functionality through rich set of function libraries
Gateway for other professional languages like C  C++  Java
C is used:
System software Compilers, Editors, embedded systems
data compression, graphics and computational geometry, utility
programs
databases, operating systems, device drivers, system level
routines
there are zillions of lines of C legacy code
Also used in application programs

Software Development Method
Requirement Specification
– Problem Definition
Analysis
– Refine, Generalize, Decompose the problem definition
Design
– Develop Algorithm
Implementation
– Write Code
Verification and Testing
– Test and Debug the code

Development with C
Four stages
 Editing: Writing the source code by using some IDE or editor
 Preprocessing or libraries: Already available routines
 compiling: translates or converts source to object code for a specific
platform source code -> object code
 linking: resolves external references and produces the executable
module
 Portable programs will run on any machine but…..
 Note! Program correctness and robustness are most important
than program efficiency

Programming languages
Various programming languages
Some understandable directly by computers
Others require “translation” steps
– Machine language
• Natural language of a particular computer
• Consists of strings of numbers(1s, 0s)
• Instruct computer to perform elementary
operations one at a time
• Machine dependant

Assembly Language
– English like abbreviations
– Translators programs called “Assemblers” to convert
assembly language programs to machine language.
– E.g. add overtime to base pay and store result in gross
pay
LOAD BASEPAY
ADD OVERPAY
STORE GROSSPAY

High-level languages
– To speed up programming even further
– Single statements for accomplishing substantial tasks
– Translator programs called “Compilers” to convert
high-level programs into machine language
– E.g. add overtime to base pay and store result in
gross pay
grossPay = basePay + overtimePay

History of C
Evolved from two previous languages
– BCPL , B
BCPL (Basic Combined Programming Language) used
for writing OS & compilers
B used for creating early versions of UNIX OS
Both were “typeless” languages
C language evolved from B (Dennis Ritchie – Bell labs)
** Typeless – no datatypes. Every data item occupied 1 word in memory.

History of C
Hardware independent
Programs portable to most computers
Dialects of C
– Common C
– ANSI C
• ANSI/ ISO 9899: 1990
• Called American National Standards Institute ANSI C
Case-sensitive

C Standard Library
Two parts to learning the “C” world
– Learn C itself
– Take advantage of rich collection of existing functions
called C Standard Library
Avoid reinventing the wheel
SW reusability

Basics of C Environment
C systems consist of 3 parts
– Environment
– Language
– C Standard Library
Development environment has 6 phases
– Edit
– Pre-processor
– Compile
– Link
– Load
– Execute

Editor DiskPhase 1
Program edited in
Editor and stored
on disk
Preprocessor DiskPhase 2
Preprocessor
program processes
the code
Compiler DiskPhase 3
Creates object code
and stores on disk
Linker DiskPhase 4
Links object code
with libraries and
stores on disk

LoaderPhase 5
Puts program in
memory
Primary memory
CPUPhase 6
Takes each instruction
and executes it storing
new data values
Primary memory

Simple C Program
/* A first C Program*/
#include <stdio.h>
void main()
{
printf("Hello World n");
}

Simple C Program
Line 1: #include <stdio.h>
As part of compilation, the C compiler runs a program
called the C preprocessor. The preprocessor is able to
add and remove code from your source file.
In this case, the directive #include tells the
preprocessor to include code from the file stdio.h.
This file contains declarations for functions that the
program needs to use. A declaration for the printf
function is in this file.

Simple C Program
Line 2: void main()
This statement declares the main function.
A C program can contain many functions but must
always have one main function.
A function is a self-contained module of code that can
accomplish some task.
Functions are examined later.
The "void" specifies the return type of main. In this case,
nothing is returned to the operating system.

Simple C Program
Line 3: {
This opening bracket denotes the start of the program.

Simple C Program
Line 4: printf("Hello World From Aboutn");
Printf is a function from a standard C library that is used
to print strings to the standard output, normally your
screen.
The compiler links code from these standard libraries to
the code you have written to produce the final
executable.
The "n" is a special format modifier that tells the printf
to put a line feed at the end of the line.
If there were another printf in this program, its string
would print on the next line.

Simple C Program
Line 5: }
This closing bracket denotes the end of the program.

Escape Sequence
n new line
t tab
r carriage return
a alert
backslash
” double quote

Memory concepts
Every variable has a name, type and value
Variable names correspond to locations in computer
memory
New value over-writes the previous value– “Destructive
read-in”
Value reading called “Non-destructive read-out”

Arithmetic in C
C operation Algebraic C
Addition(+) f+7 f+7
Subtraction (-) p-c p-c
Multiplication(*) bm b*m
Division(/) x/y, x , x y x/y
Modulus(%) r mod s r%s

Precedence order
Highest to lowest
• ()
• *, /, %
• +, -

Example
Algebra:
z = pr%q+w/x-y
C:
z = p * r % q + w / x – y ;
Precedence:
1 2 4 3 5

Example
Algebra:
a(b+c)+ c(d+e)
C:
a * ( b + c ) + c * ( d + e ) ;
Precedence:
3 1 5 4 2

Decision Making
Checking falsity or truth of a statement
Equality operators have lower precedence than
relational operators
Relational operators have same precedence
Both associate from left to right

Decision Making
Equality operators
• ==
• !=
Relational operators
• <
• >
• <=
• >=

Summary of precedence order
Operator Associativity
() left to right
* / % left to right
+ - left to right
< <= > >= left to right
== != left to right
= left to right

Assignment operators
=
+=
-=
*=
/=
%=

Increment/ decrement operators
++ ++a
++ a++
-- --a
-- a--

Increment/ decrement operators
main()
{
int c;
c = 5;
printf(“%dn”, c);
printf(“%dn”, c++);
printf(“%dnn”, c);
c = 5;
printf(“%dn”, ++c);
return 0;
}
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C PROGRAMMING

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