Computers: Tools for an Information Age

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ComputersTools for an Information Age

• Chapter 15
• Programming and Languages
• Telling the Computer What to Do

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Objectives

• Explain how to define a problem, plan the
  solution, and then code, compile, debug, and
  document the program
• List and describe the levels of programming
  languages machine, assembly, high level, very
  high level, and natural
• Describe the major programming languages that are
  in use today
• Explain the concepts of object-oriented
  programming

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Programming

• Program a set of detailed, step-by-step
  instructions that directs the computer to do what
  you want it to do
• Programming language an artificial language
  that defines a set of rules (syntax) used to
  generate or to express computer programs

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A Typical Program (convert feet to inches)
include ltiostreamgt int main () int
Feet, Inches Feet 6 Inches Feet
12 cout ltlt Height is " ltlt Inches ltlt "in. ltlt
endl return 0 // end main
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The Programming Process

• Five main steps
• Defining the problem
• Planning the solution
• Coding the program
• Testing the program
• Documenting the program

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Defining the Problem

• Develop a written agreement that specifies
• The input data
• The desired output
• The processing required to convert
• Sometimes, the programmer receives a written
  specification from the systems analyst
• Other times, the programmer meets with users
  directly

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Planning the Solution

• Algorithm
• a logical arithmetical or computational procedure
  that ensures the solution of a problem
• logic control
• Plan the algorithm
• Flowchart a pictorial representation of the
  algorithm

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Coding the Program

• Translating the algorithm from the planning stage
  into a programming language
• All languages have syntax rules
• Similar to grammatical rules
• The computer will reject a program with even a
  minor syntax error
• Programs can be keyed into the computer by using
  a text editor

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Compiling, Debugging and Testing the Program

• Compiler translates the program (source module)
  into a machine language version (object module)
• detects syntax errors
• object module will be linked to create a .exe
  file (load module)
• Debugging and Testing Detects logical errors

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Documenting the Program

• Materials are generated at each part of the
  process
• Common examples of documentation
• Flowchart and/or pseudocode
• Comments within the source code
• Testing procedures
• Layouts of input and output records
• A narrative description of the program

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Levels of Languages

• Lower-level languages more like the 0s and 1s
  the computer itself uses
• Higher-level languages more like the languages
  people use
• Divided into five generations

• Machine language
• Assembly languages
• High-level languages
• Very high-level languages
• Natural languages

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Machine Language

• Programs and memory locations are written in
  strings of 0s and 1s
• Problems with machine languages
• Programs are difficult to write and debug
• Each computer has its own machine language
• Only option available to early programmers

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Assembly Languages

• Substitute mnemonic codes for 0s and 1s
• For example, Add for add, Comp for compare, etc.
• Use names rather than binary addresses for memory
  locations
• Require an assembler to translate the program
  into machine language
• Still used for programming chips and writing
  utility programs

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High-Level Languages

• Transformed programming
• Programmers could focus on problem solving
  problems rather than manipulating hardware
• Programs could be written and debugged much more
  quickly
• Requires a compiler to convert the statements
  into machine language
• Each computer has its own version of a compiler
  for each language

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Very High-Level Languages

• Also called fourth-generation languages (4GLs)
• Considered nonprocedural languages
• The programmer specifies the desired results, and
  the language develops the solution
• Programmers can be about 10 times more productive
  using a fourth-generation language than a
  third-generation language

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Natural Languages

• Resemble written or spoken English
• Programs can be written in a natural syntax,
  rather than in the syntax rules of a programming
  language
• The language translates the instructions into
  code the computer can execute

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Major Programming Languages

• FORTRAN
• COBOL
• BASIC
• Visual Basic
• C / C
• Java

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FORTRAN

• The first high-level language
• Stands for FORmula TRANslator
• Used primarily for engineering, mathematical, and
  scientific tasks

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COBOL

• Stands for COmmon Business-Oriented Language
• Used primarily for business requirements
• Processes large data files
• Produces well-formatted reports

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BASIC

• Stands for Beginners All-Purpose Symbolic
  Instruction Code
• Developed to teach programming to college
  students
• Became very popular with the introduction of the
  microcomputer

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Visual Basic

• Allows programmer to create Windows-like user
  interfaces
• Programmer drags a control (button, text box,
  etc.) onto the form
• VB creates the code associated with that control
• VB is event-driven
• The user controls the program

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C / C

• Originally designed to write systems software
• Offers the ease of use of a high-level language
  with the efficiency of an assembly language
• Very portable can be used with virtually every
  combination of computer and operating system

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Java

• A network-friendly programming language that
  permits a piece of software to run directly on
  many different platforms
• Allows programmers to write one version of the
  program, rather than a separate version of each
  platform
• Very useful for Internet development
• Java applets can run in the users Web browser

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Object-Oriented Programming

• Object a self-contained unit that contains both
  data and its related functions
• Key terms in object-oriented programming
• Encapsulation an object isolates both its data
  and its related instructions
• Attributes facts that describe the object
• Also called properties
• Methods instructions that tell the object to do
  something
• Messages an outside stimulus that results in
  the change of the state of an object

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Using Objects

• Programmers define classes of objects
• The class contains all attributes that are unique
  to objects of that class
• An object is an instance (occurrence) of a class
• Objects are arranged hierarchically in classes
  and subclasses
• Subclasses are derived from classes
• Inheritance a subclass possesses all attributes
  of the class from which it is derived
• Additional attributes can be coded in the
  subclasses

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Activating the Object

• A message is sent to the object, telling it to do
  something
• The objects methods tell it how to do it
• Polymorphism each object has its own way to
  process the message
• For example, the class may have a Move method,
  but each subclass implements that method
  differently

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Object-Oriented Languages

• Java
• C
• Visual Basic

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Java

• A pure object-oriented program
• Used to create small programs called applets
• Applets can be delivered over the Web and run on
  any platform

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C

• An enhancement of the C language
• Includes all features of C
• Adds support for object-oriented programming
• Can be used as simply an improvement of C,
  without the object-oriented features

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Visual Basic

• Previous versions supported some object
  technology
• The current version, VB.NET, is the first to
  support inheritance and polymorphism
• These two traits are required for a true
  object-oriented language