Programming and Languages

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Programming and Languages

• Telling the Computer What to Do

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What is a program?

• A program is a detailed set of step by step
  instructions that directs the computer what to
  do
  
• Programs are written in programming languages
  which are a set of rules that allow you to write
  programs

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What do programmers do?

• Programmers obviously write programs
• Main tasks are to convert everyday problems into
  computer instructions
  
• Example a programmer might write a program that
  subtracts from your bank account balance when you
  visit the ATM

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The Programming Process

• Defining the problem
• May receive instructions from the systems
  analyst
  
• May have to meet with the user
• Eventually a written agreement is agreed upon
  that spells out the specifics of the program

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The Programming Process Continued

• Planning the solution
• Design an algorithm, which is a detailed, step
  by step solution to the problem
  
• Programmer can design this in
• Pseudocode which is nonstandard English which
  allows the programmer to spell the steps out in
  some detail without using a programming language
  
• Flowchart-graphical depiction of the process
  where symbols represent actions and arrows
  represent sequence
  
• Programmers may also use desk checking which is a
  process that requires the programmer to run
  through a mock version of the program on paper

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The Programming Process Continued

• Coding the project
• Done in a computer language which has its own set
  of rules called syntax
  
• Text is entered into a programming tool or a text
  editor, which may be a part of an integrated
  development environment (IDE)

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Testing the program

• Translation is the process of translating the
  instructions into binary so the computer can
  understand it.
  
• This is done with a compiler that takes the
  source module (what you wrote) and translates it
  into the object model (the binary version the
  computer understands)
• Load module is created when there are no more
  detectable errors in the program and the onject
  module is linked to prewritten modules using a
  linkage editor or the linker

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Testing Continued-Debugging

• Syntax errors, which are violations of the
  language rules, should be detected and corrected
  before the computer compiles
  
• Harder to find and fix, are logic errors, called
  bugs. These errors are generally errors in
  planning or the solution to the problem.
  
• Fixing logic errors is called debugging.

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Documenting the Program

• Once the program is complete, instructions and
  documentation that has been generated in the
  entire process is combined
  
• This can include the flowchart, descriptions of
  problems, narrative descriptions of the program,
  and code listings.

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Levels of Language

• Five common levels
• Machine language
• Assembly language
• High-level language
• Very high-level language
• Natural language

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Machine Language

• Series of 1s and 0s that the computer can
  understand
  
• All programs must be translated into machine
  language or binary
  
• In early days of computer it was the only way to
  program but was very difficult to read and write
  

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Assembly Language

• Next step up from machine languages but is still
  very basic and hard to understand
  
• At the time however it was a great leap from
  machine
  
• Allows for abbreviations such as A for add and
  STO for store
  
• Also allowed names for storage locations instead
  of the binary address
  
• Needs an assembler to translate it to machine
  language

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High-level language

• Developed in the early 60s
• Did not require the programmer to have detailed
  knowledge of the computer hardware
  
• Created certain languages for certain types of
  problems
  
• Increased productivity greatly
• Still requires translators to convert to machine
  language

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Very High-Level Language

• Also called fourth generation or 4GL
• First nonprocedural language (did not consist of
  step by step instructions)
  
• Programmer specifies the results desired and the
  computer figures out the best solution
  
• Productivity greatly increased
• Query language, which is an iteration of a 4GL
  are used to retrieve data from databases

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Choosing a Language

• Many times chosen for you by the business
• Can be affected if your program will interact
  with other programs or databases already written
  
• Generally you will choose the language you are
  most familiar and productive with

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Major Programming Languages-A Short Intro

• FORTRAN (FORmula TRANslation)
• one of the first high-level languages created.
• Used mostly for mathematic and scientific
  problems because of its ability to represent
  complex mathematical equations.
  
• Newer languages are replacing FORTRAN

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COBOL (COmmon Business Oriented Language)

• Designed specifically for business applications
• Very verbose meaning it is very much like
  English
  
• Still in use today
• Easy to understand because it is so verbose but
  many programmers dislike it because it takes
  longer to write
  

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BASIC (Beginners All Purpose Symbolic
Instruction Code)

• Created by professors to teach programming to
  students
  
• Became popular with the PC because it is easy to
  understand and the compiler takes very little
  memory
  
• Has all but disappeared and been replaced by
  Visual Basic

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Visual Basic

• One of the first visual development environments
• Allows users to design complex interfaces using
  items such as buttons, menus, and scrollbars.
  
• Revolution in the way the user interacts with the
  program as compared to other programs. Users can
  select what they want to do using the interface
  instead of being controlled by the program and
  only providing input when asked for.

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RPG (Report Program Generator)

• A precursor to the 4GL languages
• Developed by IBM to allow the rapid creation of
  reports from data
  
• Reports can be created much quicker than using
  its business counterpart at the time, COBOL.

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C

• Developed in the 70s to write system software but
  has been adapted to be general use
  
• Combines efficiency of assembly with the features
  of a high-level language
  
• Main selling point is its portability. There are
  compilers for all platforms (hardware and
  software combined)
  
• C quickly becoming replaced by its programming
  cousin C

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Java

• Lots of media attention
• Developed by Sun Microsystems to run natively on
  many different platforms
  
• Derivative of C
• Does not require programmer to write to a certain
  platform
  
• Because of this can be very popular for internet
  applications

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Object Oriented Programming (OOP)

• Relatively new approach to programming
• What is an object?
• Example a car can be an object
• The car has properties such as its color and
  shape
  
• The car has functions, to drive, to stop, turn,
  etc.
  
• In a programming environment, the object is a
  self-contained unit that contains both data and
  functions
  
• Dr. Kirsten Nygaard, a Norwegian computer
  scientist developed the idea of object
  orientation in 1969
  

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More on objects

• The self-contained nature of the object is called
  encapsulation
  
• The aspects that describe the object are called
  the attributes
  
• The functions or the instructions of the object
  are called methods or operations

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Even More on Objects

• Methods are activated by an outside stimulus
  called a message that results in the change of
  the state of an object
  
• Classes are groupings of objects that contain
  attibutes that are unique to objects of the
  class
  
• Subclasses can be formed also in a hierarchical
  organization
  
• All subclasses automatically posses the
  attributes of the class through inheritance

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Activating the Object

• The message is sent to the object and relays what
  needs to be done and the methods of the object
  tell the object how to do it.
  
• Polymorphism is the ability of an individual
  object to know how, using its methods, to process
  the message in an appropriate way.

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OOP Languages

• C, an enhanced version of C which supports
  object-oriented programming is the most popular
  OOP software
  
• Java is gaining some support as an OOP which is a
  pure OOP
  
• Relatively new on the market is C by Microsoft
  which is optimized for the Windows environment
  
• New additions to Visual Basic, including
  inheritance and polymorphism, meet the criteria
  for an object oriented programming language

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Why Use OOPs

• The main advantage is the ability to build and
  reuse objects
  
• For example, an object that calculates tax can be
  used over and over throughout a sales program
  
• Saves time and debugging once the object is
  functional