An introduction to Computer Science ITM 171 Chapters part of 7 and all of 8

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An introduction to Computer ScienceITM
171Chapters (part of) 7 and (all of) 8

• Programming Languages

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Examples of Programming Languages

• BASIC
• FORTRAN
• COBOL
• PASCAL
• C
• C
• JAVA

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Why do we have so many different programming
languages?

• Each language was designed to meet specific
  needs. FORTRAN was designed with engineering
  applications in mind COBOL was designed with
  report generation in mind.
• Just as we have different types of vehicles for
  different types of transportation needs, we have
  different types of programming languages for
  different types of processing needs.

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2 WAYS TO CATEGORIZE PROGRAMMING LANGUAGES

• 1. By generation
• 2. By philosophy or paradigm

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1. BY GENERATION

• First
• Second
• Third
• Fourth

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First Generation Language

• The earliest pioneers of programming actually set
  the ON/OFF switches to represent the op codes and
  operands that made up programming statements.
• Writing programs for even simple processes was
  tedious and error prone.

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Machine Language looks like this

• 010001 0011100 000111
• 001101 1100111 110001
• 010101 0010111 001110
• 011000 0101011 101011

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Second Generation Language (aka Assembly language)

• Assembly language simplified a programmers job
  by allowing the programmer to use mnemonics in
  place of the 0s and 1s in the program.
• Mnemonics are memory aids - alphabetic
  abbreviations for instructions. For example,
  ADD may represent the op code 0101001 for
  addition, or MUL may represent the op code
  101010 for multiplication.
• Programs written in assembly language require an
  assembler to translate the assembly language code
  into machine language so the program can be run.
• One line of programming code in assembly language
  translates into one line of programming code in
  machine language.

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Assembly Language looks like this
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Assembly language disadvantages

• The programmer must manually manage the
  movement of data items between and among memory
  locations.
• The programmer must take a microscopic view of
  tasks
• Assembly language is machine specific (not
  portable)
• The language is not very English-friendly

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Third Generation Languages

• Most languages that you hear of today are third
  generation languages. Examples FORTRAN, COBOL,
  BASIC, C, C, JAVA, etc.
• 3rd generation languages allow the programmer to
  use instructions that more closely resemble the
  English language.
• One line of programming code in 3rd generation
  language translates into several lines of
  programming code in machine language.
• 3rd generation languages must be translated into
  machine language using a compiler or interpreter.

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Third Generation Language looks like this (BASIC)

• input Enter name names
• input Enter hours hours
• input Enter rate rate
• grosshours rate
• fedtax .2 gross
• socsec .07 gross
• net gross - fedtax - socsec
• print names, net
• end

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What 3GLs provide that 2GLs dont

• The programmer need not manage the details of
  movement of data
• The programmer can take a macroscopic view of
  tasks
• Programs are portable - not machine specific
• The language is more English-friendly

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Fourth Generation Languages

• Fourth-generation languages are programming
  languages closer to human languages than typical
  high-level programming languages. Most 4GLs are
  used to access databases.

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Fourth Generation Language looks like this

• FIND ALL RECORDS WHERE NAME IS "SMITH"

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2. Categorizing languages by paradigm (philosophy)

• IMPERATIVE (PROCEDURAL) LANGUAGES (Like C, COBOL,
  BASIC, FORTRAN)
• OBJECT ORIENTED LANGUAGES (Like C, JAVA, Visual
  BASIC)
• SPECIAL PURPOSE LANGUAGES
• FUNCTIONAL LANGUAGES
• LOGIC LANGUAGES

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IMPERATIVE (PROCEDURAL) LANGUAGES

• Philosophy A program is a series of tasks that
  can be divided into sub-tasks.

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The Procedural approach to application
development

• Top-down, stepwise refinement.
• High-level goals and processes are defined first.
  Then high-level processes are divided into tasks,
  who are in turn divided into sub tasks and each
  sub-task can be coded separately and then
  integrated into the application.
• A program written in an imperative language
  consists of a sequence of statements that
  manipulate data items that is, they change the
  contents of memory cells.
• It is the programmers task to devise the
  appropriate step-by-step sequence of imperative
  commands that will accomplish the desired task.
• Examples FORTRAN, COBOL, Pascal, C, Ada

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FORTRAN

• Good for mathematically intensive programs (Can
  be used to tell the computer how to carry out
  extended precision arithmetic)
• FORTRAN is still an effective language for
  engineering applications

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COBOL

• Good for business applications which are not
  mathematically intensive but require a lot of
  repetitive (record) processing and report
  generation (such as payroll applications or
  inventory update programs)
• In the 1970s, payroll and inventory data were
  stored as records in a master file. Data needed
  for weekly updates were stored in a transaction
  file. Programs were written to use the data in
  the transaction file to create a new (updated)
  master file. COBOL was good at handling this type
  of program.

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PASCAL

• A language designed for teaching computer science
  majors how to program.
• It is designed to be relatively easy to learn
• Rarely used in real business or engineering
  applications

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C

• C has the power of a high level language but the
  control of a low level language
• Writing in C allows you to think at a high level
  of abstraction but also allows you to have
  control over memory access and storage.
  Therefore, it is good for writing programs that
  are need to be (1) highly efficient and (2) need
  direct control over memory access and allocation
  such as an operating system program (Unix) or a
  compiler. (Yes, the compiler is also a program!)

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OBJECT ORIENTATED LANGUAGES

• Philosophy A program is a series of objects that
  have attributes and behaviors (procedures).

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The OO approach to application development

• Instead of using task-focused approach where one
  large task is subdivided into smaller tasks and
  each task is coded separately, an OO programmer
  uses an object-focused approach to designing an
  application.
• In other words, program design starts with
  enumerating the objects involved in the
  application.

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Objects Examples

• In a word processing program, you have objects
  such as letter, paragraph, and document. A
  document object is made up of paragraph objects
  which are in turn, made up of letter objects.
• In a spreadsheet program, you have objects such
  as cell, column, row, block, pie chart, pie chart
  title, line graph, legend, x-axis, y-axis. A
  graph object is made up of a title object, an
  x-axis object, a y-axis object, a gridline
  object, data point objects, and a legend object.
• In a presentation program (such as this one), you
  have objects such as slide, slide title, bullet
  point, graphic image, etc. A slide object is made
  up of a slide title object, slide bullet point
  objects and maybe one or more graphic image
  objects.
• In a bank account processing application, you
  have objects such as customer, checking account,
  savings account, loan account.

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The OO approach continued...

• After identifying the objects that are relevant
  to the application, the program determines what
  attributes the object must have and what
  procedures need to be performed on the objects.
• For example, the object bank account can have
  attributes open date, balance, owner,
  over-draft limit, etc.
• An object bank account can have procedures such
  as update balance, close, open, print
  statement, etc.

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Other examples of object attributes and processes

• A letter object in a word processing document has
  attributes such as a size, a font style, a color,
  a boldness setting, an underline setting. etc.
• Certain processes (behaviors) can be performed on
  letter objects such as create, change size,
  change color, move or delete.
• Each time you type a letter you are creating an
  instance of a letter object.

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Here is what an object definition looks like

• class date
• public
• void changeDate (int month, int day, int year)
• void displayDate( )
• private
• int month
• int day
• int year
• date payDay // This creates a date object named
  PayDay

Two Methods(behaviors)
Three attributes
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Does OO abandon the idea of the procedural
approach to application development?

• No. The procedures (i.e. algorithms) reside in
  the functions which perform processes on objects.
• Instead of one big long procedure that runs from
  start to finish (like a payroll processing
  application), there are several short procedures
  and the user controls their order and frequency
  of execution (often by using mouse clicks).

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Programming in an OO language means

• 1. Defining and using objects their attributes
  and the processes (behaviors) that can be
  performed on them or that they can perform on
  other objects (behaviors).
• 2. Knowing how to use (and extend) predefined
  objects Many objects have already been created
  by someone else and stored in class (object)
  libraries. You can download or purchase class
  libraries that contain commonly-used objects such
  as Window, scroll bar, or icon and
  customize them for your own purposes. (Thus, the
  idea of reusable code.)

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OOP Terminology

• Class - the definition of an object. A class
  contains all of the attributes and all of the
  behaviors that describe an object. First you
  define a class/object then you instantiate it.
• Encapsulation - the concept of combining an
  objects attributes and behaviors into one
  package - the class.
• Abstraction - the concept of making the
  implementation details of a class transparent to
  the user. If a programmer obtains a class
  definition from someone else (a class library),
  the user need only know how to create an instance
  of the class and how to tell it to perform
  procedures. The programmer need NOT know any more
  implementation details. (Example You need to
  know how to start and stop the engine of your
  car. You need NOT know how the engine actually
  works.)
• Inheritance - the concept that you can create a
  new class by extending a base class. For example,
  class BOX drawn on screen can be extended to
  class WINDOW.

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JAVA

• Good for writing programs that use multi-media
  and that need to run on many different types of
  computers.

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C

• A language developed as an extension of the C
  language.
• Emphasizes software reuse

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SPECIAL PURPOSE LANGUAGES

• SQL - Structured Query Language - A language
  designed to extract useful information from a
  database.
• PERL - Practical Extraction and Report Language -
  used to scan arbitrary text files and extract
  various kinds of information that is contained
  within the text and print reports based on the
  extracted information.
• Perl is often used to process data submitted via
  input forms embedded in Web pages. The data
  submitted via on-screen form will be sent to the
  server as a continuous stream of text. Perl can
  be used to parse the string and structure the
  data so it can be added to a database.
• HTML - Hypertext Markup Language - used to create
  documents that contain formatting codes
  understandable to a Web browser.

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Functional Programming (LISP) -

• Philosophy a program is a series of function
  calls
• A function is a procedure which transform a
  series of inputs into a single output.
• The programmer to not have to focus on the
  step-by-step procedures.
• LISP is the well-known functional programming
  language.

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Logic programming-

• Philosophy A program consists of a collection of
  facts and rules which are used to infer other
  facts to derive knowledge
• Prolog is the most well-know logic language.

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Parallel Programming - Two approaches

• SIMD (single instruction steam/multiple data
  stream) - a single control unit broadcasts a
  single program instruction to multiple ALUs,
  each of which carries out that instruction on its
  own local data stored in its local memory.
• MIMD (multiple instruction stream/multiple data
  stream) - numerous inter-connected processors
  execute their own programs on their own data,
  communicating results as necessary.