Introduction to 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

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

Basics of C Environment Primary memory Puts program in memory Loader Phase 5 Primary memory Takes each instruction and executes it storing new data values CPU Phase 6

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; } 5 5 6 5 6 6

Thank You • Thank You

Introduction to C Programming