Introduction to Programming in C

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Introduction to Programming in C

• Class 1
• 01/13/2003
• Rohit Valsakumar

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Computer Systems

• Program A set of instructions that commands the
  computer to perform a certain task.
• Software The collection of programs running on a
  computer e.g. editors, browsers, operating system
  etc.
• Hardware The physical components that make up a
  computer e.g., motherboard, monitor, keyboard etc.

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Hardware

• Three main types of computers
• PCs, workstations, mainframes

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Memory

• Stores the input
• Stores intermediate results of operations
  performed by CPU
• Used by CPU as a scratch pad
• Two distinct forms of memory
• Main memory e.g. RAM
• Secondary memory e.g. Hard disks, tape drives,
  CD-ROMS etc.

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Secondary memory

• Non volatile
• Very cheap
• Used for long term storage

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Main memory

• Volatile
• Expensive
• Used for intermediate storage

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Main memory

• Is designed as a long list of numbered locations
  called as memory locations
• Each memory location stores a string of 0s and 1s
• Each 0 or 1 is called a bit
• In most computer each memory location can hold at
  most eight bits called a byte
• The number of each byte is its address

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Main memory
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Software

• Types of programs running on the computer
• Operating System (most important program)
• Editors
• Compilers
• Games
• Scientific software
• Operating System is responsible for allocating
  and managing the resources of the computer among
  the various programs that run on it

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Program

• Input to a computer is made of two components
  data and program
• The program is a set of instructions that the
  computer follows to process the data and generate
  the output
• This activity is called as a process

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Program

• The program or set of instructions can be written
  in various languages such as
• Machine language e.g. 1100100111001
• Assembly language e.g. MOV A, B
• High-level language e.g. if cond true ..
• It is very difficult to write programs in machine
  level or assembly languages because
• Code is not portable across various platforms
• Difficult to maintain, debug or extend
• Impossible to write long programs

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High Level Languages

• High level languages like C, C, Pascal were
  developed to overcome the above problems
• It resembles human language in many ways
• It becomes easier to read and write programs
• Larger programs can be written in a short time

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High Level Languages

• Computers dont understand high level languages,
  they understand only machine language
• Two programs that convert the high level language
  into machine language compilers and linkers
• Compilers A program that translates a high level
  language like C code to a machine language
• Input program is called source program or source
  code
• Translated version is called object code
• Linkers Linkers combine the object code of the
  source code with the object code of the routines
  (such as input and output routines)

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Algorithm

• Algorithms - An algorithm is a step-by-step
  finite sequence of instructions that describe how
  to perform a computation.
• Example To add numbers 1 to 100 we can use the
  following algorithms
• 123499100 5050
• 0100 100 199 100 298 100 50 (50
  100) 50 5050
• Sum N(AB)/2
  Where N Number
  of terms to be added (100)
  A First Number to be added (1)
  B The
  Last Number to be added (100) Thus
  Sum 100(1100)/2 5050

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Program Design

• Divided into two phases
• Problem solving phase
• Involves expressing the solution to the problem
  in the form of an algorithm
• Implementation phase
• Translate the algorithm generated in problem
  solving phase into a computer program
• Caution do not ever omit the problem solving
  phase whatever be the reason
• The two phase process will produce a correctly
  working code with minimum hassle.
• Both phases should include testing to minimize
  error and error propagation
• Please refer to Display 1.7 pg 17 of the text
  book

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Object Oriented Programming

• A program is viewed as a collection of
  interacting objects
• The behavior of each object is captured by an
  algorithm for that object
• Thus in OOP programming involves designing the
  objects and the algorithms they use
• E.g. to design a card game each card can be
  thought of as an object

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The Software Life Cycle

• Very important in the design of large software
  products
• Six main stages
• Analysis and specification of the task
• Design of the software
• Implementation (coding)
• Testing
• Maintenance and evolution of the code
• Obsolence

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A small C program

• includeltiostream.hgt
• int main()
• int i 10
• cout ltlt Hello Worldltlt endl
• cin gtgt i
• cout ltlt i
• cin ltlt i
• return 0

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Testing and debugging

• Bug Error or mistake in the code is called a bug
• Debugging Process of eliminating bugs

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Types of errors

• Specification errors Occurs when the
  specification of the problem itself has errors in
  it (very hard to detect and correct)
• Syntax errors Violation of the syntax (grammar
  rules) of the programming language e.g. missing
  semicolon or brace (gets caught by the compiler)
• Run-time errors Errors that are detected only
  when the program is run on a computer e.g. divide
  by zero (usually detected at run time and error
  message displayed by the system)
• Logic errors Mistakes in the algorithm or in the
  translation of the algorithm into program e.g.
  using wrong operators