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 withprogrammers.

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

Programming languages 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

Programming languages

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

Basics of C Environment

Editor DiskPhase 1

Program edited in Editor and storedon disk

Preprocessor DiskPhase 2

Preprocessor program processesthe code

Compiler DiskPhase 3

Creates object code and stores on disk

Linker DiskPhase 4

Links object code with libraries and stores on disk

Basics of C Environment

LoaderPhase 5

Puts program in memory

Primary memory

CPUPhase 6

Takes each instructionand executes it storingnew 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 About\n");

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(“%d\n”, c);printf(“%d\n”, c++);printf(“%d\n\n”, c);

c = 5;printf(“%d\n”, c);printf(“%d\n”, ++c);printf(“%d\n”, c);

return 0;}

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