Computer Languages

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Computer Languages
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Machine Languages

• It is the only language the computer understands.
• It is made of 0s and 1s.
• They must be in 0s and 1s because the internal
  circuit of a computer is made up of switches,
  transistors, and other electronic devices that
  can be either on or off (1 or 0 respectively).

• Example of Machine Language (on page167)
• 1 00000000 00000100 0000000000000000
• 2 01011110 00001100 11000010 0000000000000010
• 3 11101111 00010110 0000000000000101

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Symbolic Languages

• Developed by Grace Hopper, a mathematician for US
  Navy in 1950s
• It uses symbols or mnemonics to represent machine
  language
• A program called an assembler is used to
  translate symbolic code into machine language
• Theyre also known as assembly languages because
  they have to be assembled

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Symbolic Languages Contd.
Example multiplication program page 168 1 entry
main, mltr2gt 2 sub12 12, sp 3 jsb CMAIN_ARGS 4
movab CHAR_STRING_CON 5 6 pushal -8(fp) 7
pusal (r2) 8 calls 2, read 9 pushal
-12 (fp) 10 pushal 3 (r2) 11 calls 2,
read 12 mull3 -8 (fp), -12 (fp), - 13pusha
6 (r2) 14 calls 2, print 15 clrl r0 16 ret
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High-Level Languages

• Developed to improve programmer efficiency from
  symbolic languages to change focus from the
  computer to the problem being solved
• Theyre portable to different computers
• They still need to be converted to machine
  languages in a process called compilation
• Examples include
• BASIC
• COBOL
• Pascal
• Ada
• C

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Natural Languages

• These include the language that people speak in
  their daily lives
• These can include
• English
• Spanish
• German
• French
• Italian
• The idea is to use ones natural language to give
  the computer orders
• This has only limited use today

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Building a Program

• Writing and Editing Programs
• Use a text Editor to write programs
• When youre done you save your program to the
  disk (known as a source file) and it will be
  input to the compiler
• Compiling Programs
• Translates inf in a source file into machine
  language
• Made of 2 separate programs the preprocessor
  the translator
• Preprocessor reads the source code and prepares
  it for the translator. While preparing the code
  it scans for special commands (preprocessor
  directives) that tell it to look for special code
  libraries, make substitution in the code, other
  ways to prepare the code for translation into
  machine language. The result of this processing
  is called the translation unit.
• Translator converts the translation unit into
  machine language. This code in machine language
  is called the object module
• Linking Programs
• A high-level language has many subprograms, some
  of which are written in the program some exist
  elsewhere and have to be attached to the program
  (ex I/O processes)
• The linker assembles all of these functions into
  the final executable function.

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Program Execution

• Use the Operating System (OS) command (ex. run)
  to load the program into primary memory execute
  it.
• Loader it is an OS program responsible for
  loading the program into the memory
• Program reads data for processing either from the
  user or from a file
• After the program processes the data it prepares
  the output to either the monitor or to a file
• When the program is finished it tells the OS,
  which removes the program from memory

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Categories of Languages
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Procedural (Imperative) Languages

• Procedural Language a set of instructions that
  are executed one-by-one from beginning to end
  unless an instruction forces the control
  elsewhere
• Each instruction either manipulates data items or
  is a control execution.
• Examples
• FORTRAN
• COBOL
• Pascal
• C
• Ada

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FORTRAN

• FORmula TRANslation
• Designed by a group of IBM engineers was
  commercially available in 1957
• First high-level language
• Features
• High-precision arithmetic
• Capability of handling complex numbers
• Exponentiation computation (ab)

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COBOL

• COmmon Business-Oriented Language
• Designed by US Navy computer scientists
• Designed to be used as a business programming
  language
• Fast access to files and databases
• Fast updating of files and databases
• Large amounts of generated reports
• User-friendly formatted output

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Pascal

• Invented by Nikalus Wirth in 1971 in Zurich,
  Switzerland
• Named after Blaise Pascal, the 17th century
  French mathematician philosopher who invented
  the Pascaline calculator
• Designed to teach programming to novices by
  emphasizing the structured programming approach

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C Ada

• C language developed by Dennis Ritchie at Bell
  Laboratories
• Originally designed for writing Operating Systems
• Later became popular among programmers

• Ada was named after Augusta Ada Byron, the
  daughter of Lord Byron the assistant to Charles
  Babbage
• Created by US Department of Defense to be a
  uniform language used by all Department of
  Defense contractors

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Object-Oriented Languages

• The objects (a data item) the operations to be
  applied to them are tied together
• Programmer first defines and object the types
  of operations that can be applied to this object
  can use this combination invokes some or all
  of the operations defined to solve a problem
• The objects are active
• Example
• C
• Java

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C

• Developed by Bjarne Stroustrup at Bell
  Laboratories
• Uses classes to define general characteristics of
  similar objects the operations that can be
  applied to them
• 3 principles encapsulation, inheritance,
  polymorphism
• Encapsulation the idea of hiding the data some
  operations that can be performed on the data
  inside the object
• Inheritance an object can inherit from another
  object
• Polymorphism you can define several operations
  with the same name that can do different things
  in related classes

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Java

• Developed by Sun Microsystems, Inc.
• Based on C C
• Its totally class oriented
• Program can be either an application or an applet
• Application stand-alone program
• Applet embedded in HTM language, stored on a
  server, run by a browser
• Class Library a collection of classes
• Multithreading a thread is a sequence of actions
  executed one after the other, Java allows for
  multithreading

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Functional Languages

• A program is considered a mathematical function
• A function is a black box that maps a list of
  inputs to a list of outputs
• It does the following
• It predefines a set of primitive (atomic)
  functions that can be used by any programmer
• It allows the programmer to combine primitive
  functions to create new functions
• Advantages over procedural language
• It encourages modular programming
• Allows the programmer to make new functions our
  of existing ones
• Examples
• LISP
• Scheme

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LISP Scheme

• LISt Programming
• Designed by researchers at MIT in the early 1960s
• Everything is considered a list

• Scheme
• Version of LISP developed by MIT in 1970s
• Defines a set of primitive functions that solves
  problems

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Declarative (Logic) Languages

• Uses the principle of logical reasoning to answer
  queries
• Based on formal logic defined by Greek
  mathematicians later developed into what is
  called first-order predicate calculus
• Logical reason is based on deduction
• One problem a program is specific to a
  particular domain because collecting all the
  facts into one programming makes it huge
• Example
• Prolog

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Prolog

• PROgramming in LOGic
• Developed by A. Colmerauer in France in 1972
• Program is made of facts and rules

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Special Languages

• HTML
• PERL
• SQL

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HTML

• Hypertext Markup Language
• Pseudolanguage that includes marks that serve as
  formatting hints links tags
• HTML file is made of texts tags
• Tagenclosed in 2 angle brackets usually come
  in pairs marks that are embedded into the text
  it can have a list of attributes , each of which
  can be followed by an equal sign value
  associated with the attribute
• HTML file (page) is stored on the server can be
  downloaded by a browser
• Browser removes the tags interprets them as
  either formatting hints or links to other files
• Allows you to embed formatting instructions in
  the file itself are stored in the text
• 2 parts
• Head the first part that contains the title of
  the page other parameters that the browser will
  used
• Body the actual contents of a page includes the
  text tags text is the actual info contained in
  a page tags define the appearance of the page

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HTML
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PERL

• Practical Extraction Report Language
• High-level language with a syntax similar to the
  C language but more efficient
• Its power is in its well-designed use of regular
  expressions that allow the programmer to parse a
  string of characters into its components
  extract the needed info

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SQL

• Structured Query Language
• Used to answer queries about databases

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Overview

• Types of languages
• Machine, Symbolic, High-Level, Natural
• Building a program
• Writing editing
• Compiling
• Linking
• Categories of Languages
• Procedural (ex FORTRAN)
• Object-Oriented (ex C)
• Functional (ex LISP)
• Declarative (ex Prolog)
• Special (ex HTML)