Programming Languages: Telling the Computers What to Do

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Programming Languages Telling the Computers
What to Do

• Chapter 16

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Objectives

• Describe what programmers do and do not do
• Explain how programmers define a problem, plan
  the solution and then code, test, 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 in use
  today
• Explain the concepts of object-oriented
  programming

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Contents

• Program
• Programmers
• The Programming Process
• Choosing a Language
• Traditional Programming
• Object-Oriented Programming
• Learning to Program

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Program

• Set of instructions written in a programming
  language that tells the computer what to do

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Programmers

• Prepare instructions that make up the program
• Run the instructions to see if they produce the
  correct results
• Make corrections
• Document the program
• Interact with
• Users
• Managers
• Systems analysts
• Coordinate with other programmers to build a
  complete system

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The Programming Process

• Defining the problem
• Planning the solution
• Coding the program
• Testing the program
• Documenting the program

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The Programming ProcessDefining the Problem

• What is the input
• What output do you expect
• How do you get from the input to the output

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The Programming ProcessPlanning the Solution

• Algorithm detailed solution to a problem
• Design tools
• Flowchart
• Pseudocode
• Desk-checking
• Structured walkthrough

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The Programming ProcessPlanning the Solution

• Accept series of numbers
• and display the average

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The Programming ProcessPlanning the Solution
Accept series of numbers and display the average
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The Programming ProcessCoding the Program

• Translate algorithm into a formal programming
  language
• Syntax
• How to key in the statements?
• Text editor
• Programming environment Interactive Development
  Environment (IDE)

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The Programming ProcessTesting the Program

• Translation compiler
• Translates from source module into object module
• Detects syntax errors
• Link linkage editor (linker)
• Combines object module with libraries to create
  load module
• Finds undefined external references
• Debugging
• Run using data that tests all statements
• Logic errors

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The Programming ProcessTesting the Program
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The Programming ProcessDocumenting the Program

• Performed throughout the development
• Material generated during each step
• Problem definitions
• Program plan
• Comments within source code
• Testing procedures
• Narrative
• Layouts of input and output
• Program listing

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Choosing a Language

• Choice made for you
• What is available?
• Required interface
• What do you know best?
• Which language lends itself to the problem to be
  solved?

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Language Generations

• Low levels closer to binary
• High levels closer to human code
• Five Generations
• Procedural Languages
• Machine language
• Assembly language
• High-level language 3GL
• Nonprocedural Languages
• Very high-level language 4GL
• Natural language 5GL

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Machine Language

• Written in strings of 0 and 1
• Only language the computer understands
• All other programming languages are translated to
  machine language
• Computer dependent

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Assembly Language

• Mnemonic codes
• Names for memory locations
• Computer dependent
• Assembler translates from Assembly to machine
  language

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3GLHigh-Level Languages

• 1960s
• Languages designed for specific types of problems
  and used syntax familiar to the people in that
  field
• FORTRAN math
• COBOL business
• Compile translates from high-level language to
  machine language

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4GLVery High-Level Languages

• Programmer specifies the desired results the
  language develops the solution
• Ten times more productive with a 4GL than a
  procedural language
• Query Languages
• Retrieve information from databases
• Easy to learn and use

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5GLNatural Languages

• Resemble natural or spoken English
• Translates human instructions into code the
  computer can execute
• Commonly used by non-programmers to access
  databases

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Third Generation LanguagesTraditional Programming

• Describe data
• Describe procedures or operations on that data
• Data and procedures are separate

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Third Generation Languages

• FORTRAN
• 1954
• Represent complex mathematical formulas
• C/C has replaced FORTRAN
• COBOL
• 1959
• Business
• Large complex data files
• Formatted business reports

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Third Generation Languages
FORTRAN
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Third Generation Languages
COBOL
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Third Generation Languages

• BASIC
• 1965
• Popularity grew with PC popularity (1970s)
• Easy to learn
• Used little memory
• RPG
• 1965
• Report generation quickly creates complex
  reports

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Third Generation Languages
BASIC
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Third Generation Languages

• Visual Basic
• 1987
• Create complex user interfaces
• Uses standard Windows features
• Event-driven user controls the program
• C
• 1972
• Efficient code
• Portability
• C
• Enhancement of C

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Third Generation Languages
C
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OOPObject-Oriented Programming

• Object
• Self-contained unit of data and instructions
• Includes
• Related facts (data)
• Related functions (instructions to act on that
  data)
• Example
• Object cat
• Data feet, nose, fur, tail
• Functions eat, purr, scratch, walk
• Cat Kitty, Susan

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OOPObject-Oriented Programming

• Encapsulation describes the objects self-
  containment
• Attributes the facts that describe the object
• Methods / operations the instructions that tell
  the object what to do
• Instance one occurrence of an object
• Messages activate methods
• Example A walk message causes Kitty to move

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OOPObject-Oriented Programming

• Class defines characteristics unique to all
  objects of that class
• Inheritance Objects of a class automatically
  posses all of the characteristics of the class
  from which it was derived
• Subclass inherits characteristics from class
  and defines additional characteristics that are
  unique

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OOPObject-Oriented Programming

• Example
• Class Animal
• Subclass Cat
• Subclass Persian cat
• Instance Kitty
• Objects can be reused

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OOPObject-Oriented Programming

• Languages
• C
• Can write both structured and object-oriented
  code
• Visual Basic
• Rudimentary features of object-oriented language

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Third Generation Languages

• Java
• Cross-platform
• Java Virtual Machine (JVM)
• Sits on top of computers regular platform
• Translates compiled Java code into instructions
  for the specific platform
• Applets

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OOPObject-Oriented Programming

• Using Objects in Business
• Class Customer
• Subclass Retail or Wholesale
• Instance John Smith
• Retail and Wholesale customers automatically
  inherit customer address since it is part of the
  Customer class

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Learning to Program

• Enroll in courses
• Read
• Use tutorials
• View Sample code
• Write code (start small)
• Use Help

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