Theory is when you know something, but it doesn't work. Practice is when something works, but you don't know why.

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• Theory is when you know something, but it doesn't
  work. Practice is when something works, but you
  don't know why.
• Programmers combine theory and practice Nothing
  works and they don't know why.
• --unknown

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• Once a new technology starts rolling, if you're
  not part of the steamroller, you're part of the
  road.
• --Stewart Brand

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Nabil Ur Rehman BICSE 3 nabil.rehman_at_niit.edu.pk Zeeshan Ahmad BICSE 3 zeeshan.ahmad_at_niit.edu.pk Jahanzeb Maqbool BIT9-A jahanzeb.maqbool_at_niit.edu.pk Bibrak Qamar BIT9-A bibrak.qamar_at_niit.edu.pk Aqsa Khalid BICSE5A aqsa_khalid_at_yahoo.com
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Introduction to C Programming

• Lecture 2

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Todays Lecture

• Software Categories
• System Software
• Application Software
• Introduction to C Language
• History
• Evolution
• Justification
• Development Environment of C

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• There are two main categories of software
• System software
• Application Software

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Evolution of programming languages

• The lack of portability between different
  computers led to the development of high-level
  languagesso called because they permitted a
  programmer to ignore many low-level details of
  the computer's hardware
• Details of procedural, non-procedural will follow
  in the lectures

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How people used to program

• Machine Language.. Damn! It was difficult
• Assembly Language. Remember ADD?
• Required too much user involvement
• To much to remember
• Less semantic
• C Language
• B Language.. Bell Labs
• Improved to C Language
• Is a compiled language

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• ANSI C

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Tools of the trade

• Editor
• Interpreter and Compilers
• Debuggers

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Integrated Development Environment(IDE)

• It contains
• Editor
• Compilers
• Debugger
• Linkers
• Loaders

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(No Transcript)
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• include ltiostream.hgt
• main ( )
• cout ltlt Welcome to SEECS

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Variable
X

• Variable

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Variable

• Pic of the memory
• 25
• 10323

name of the variable

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Variable

• Variable starts with
• Character
• Underscore _ (Not Recommended)

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Variable

• Small post box

X
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Variable

• Variable is the name of a location in
• the memory
• e.g. x 2

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Variable

• In a program a variable has
• Name
• Type
• Size
• Value

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Assignment Operator

• x 2

X
2
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Assignment Operator

• L.H.S R.H.S.
• X 3 y 4 Wrong
• Z x 4
• x 4 Z Wrong

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10
X

• X 10
• X 30

30
X
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X X 1
X
10
1

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X
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Data type

i

• int i //Declaration line

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Writing C program
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Compiler converts human readable language to a
language which is understandable by the operating
system/hardware Examples of C/C compilers of
today Visual C GCC/G DJGPP (open source for
windows like GCC) Borland C Turbo (obsolete and
not recommended)
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3 Stages of Compilation

• Stage 1 Preprocessing
• Performed by a program called the preprocessor
• Modifies the source code (in RAM) according to
  preprocessor directives (preprocessor commands)
  embedded in the source code
• Strips comments and white space from the code
• The source code as stored on disk is not
  modified.

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3 Stages of Compilation (cont)

• Stage 2 Compilation
• Performed by a program called the compiler
• Translates the preprocessor-modified source code
  into object code (machine code)
• Checks for syntax errors and warnings
• Saves the object code to a disk file, if
  instructed to do so (we will not do this).
• If any compiler errors are received, no object
  code file will be generated.
• An object code file will be generated if only
  warnings, not errors, are received.

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Object code

• It is machine language code containing various
  calls specific to operating system e.g the
  object code written by compiler is not only
  hardware dependent but also operating system
  dependent.
• So if you have linux and windows both operating
  systems then object file of compiled by one
  Operating System (OS) will not get executed on
  the other OS

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3 Stages of Compilation (cont)

• Stage 3 Linking
• Combines the program object code with other
  object code to produce the executable file.
• The other object code can come from the Run-Time
  Library, other libraries, or object files that
  you have created.
• Saves the executable code to a disk file. On the
  Linux system, that file is called a.out.
• If any linker errors are received, no executable
  file will be generated.

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Program Development Using gcc
Editor
Source File pgm.c
Preprocessor
Modified Source Code in RAM
Compiler
Program Object Code File pgm.o

Other Object Code Files (if any)
Linker
Executable File a.out
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• include ltiostream.hgt //This is pre-processor
  directive
• void main ( ) //this tells the starting point
  of your program
• int x
• int y
• int z
• x 10
• y 20
• z x y
• cout ltlt " x " //print the text on
  monitor
• cout ltlt x
• cout ltlt " y "
• cout ltlt y
• cout ltlt " z x y "
• cout ltlt z

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• int x, y, z
• int x int y int z