History of Programming Languages and Programming Language Concepts

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History of Programming Languages and
Programming Language Concepts
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What does a computer program do?
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A computer program is

• a set of instructions that tell a computer how
  to perform a particular task.

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A computer program is like

• a recipe
• A recipe is a set of instructions to tell a cook
  how to make a particular dish.
• It describes the ingredients (the data) and the
  sequence of steps (the process) needed to convert
  the ingredients into the cake.

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What is programming?
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Programming is

• -- the effort in coming up with a set of
  instructions that describe how a problem can be
  solved.

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• We always think a program is a computer
  language, but actually, programs can be in many
  languages and in many forms. Lets
  look at an example

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A simple program

• An English language example
• On the back of a shampoo bottle
• Wet Hair
• Lather
• Rinse
• Repeat

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Interpretations Assumptions..

• Notice those 4 instructions (wet hair, lather,
  rinse, repeat)makes several assumptions
• Lather also implies pouring some shampoo from
  the bottle onto either your hand or head
• Step 4 really means repeat once

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Major difference between humans computers..

• Humans have judgment free will.
• They will not follow any instruction they
  determine not required or nonsensical
• Computers will do EXACTLY what is toldwith no
  judgment or sanity checks

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!!!

• Give those instructions to your computer and
  it will neverget out of the shower!!

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So how does a program tell the computer exactly
what needs to be done?

• Just as you speak to a friend in a language that
  he/she understands, you need to 'speak' to the
  computer in a given language it understands.
• The only language that the computer understands
  is called binary or machine language.
• Programs interact with the computer using machine
  language.
• Machine language is just made up of 0s and 1s.

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How much can you communicate using only 0s and
1s?

• More than you think!!!
• but its not easy
• so right from the start, its been desired to
  have some type of translation process to get
  English translated into binary (and back)

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Think of that translation process as being like
an interpreter
Barack Obama
Chinese President Hu Jintao

• Consider the American and Chinese presidents
  talking at a summit meeting
• One speaks in English, then an interpreter
  repeats what has been said in Chinese
• The other replies in Chinese and the interpreter
  again repeats the sentence, this time in English.
  

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So lets look back at how that translation
process evolved over the years
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In the beginning there was no translation process

• Early programmers (early 1950s) actually had to
  enter the binary codes themselves, (the 1s and
  the 0s!!!)
• Instructions were entered through the front
  panel switches of the computer system.
• Coding in binary is regarded as working in a
• First Generation Programming Language (1GL)

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Initial Translation Efforts..

• Entering the 0s and 1s was very time consuming.
  
• So, effort was spent creating a language that
  would reduce this effort
• The assembler language was thus created
• It translates English equivalents (really, a
  symbolic representation) to machine language

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Example of Assembler language

• The only thing that this program does is to save
  two values in two registers and add the value of
  one to the other.
• In a high level language such as RealBasic, wed
  just do something like result 6 4

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Another Assembler example

• This program displays a character string on the
  screen 15 times

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Assembler Languages

• Developed in the mid 1950s
• Considered a low level language because
• It is specific to a particular computer
  architecture (will only run on a very specific
  computer model)
• An example If we were to write an assembler
  language program to run in H209 it would NOT
  work in H210 because we have iMacs in here and
  H210 has Mac Minis!
• And because you would have to know very low-level
  details about the computer in order to be able to
  write a program using Assembler
• Assembler language is considered a second
  generation programming language (2GL)

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Assembler languages..

• Assembler languages use a translation process
  called an assembler to translate assembly
  language statements into machine code.
• There is a11 mapping from each mnemonic
  statement into a machine instruction
• (contrast that with high level languages a
  single statement results in many machine
  instructions)

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Assembler Languages (cont)

• Some use of 2GLs (Assembler Language) still used
  today
• When direct hardware manipulation is needed or
  for critical performance
• Example device drivers, real time systems(for
  high performance)

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An improvement, but more desired

• So 2GL had its uses but more translation
  capabilities were desired
• It was desired that programming languages be more
  easily understood
• It was also desired that the same program could
  be run on different types of architectures

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3GLs

• First introduced in the late 1950s
• Introduced concept of structured programming (did
  not have to directly work with registers could
  also use algebraic expressions)
• Introduced a level of abstraction away from the
  hardware. This made it more user friendly
  making it easier to learn use
• Used translation processes called compilers and
  interpreters
• Introduced database management systems
• Early examples
• Fortran (1956) used for science math (lots of
  precision)
• COBOL (1959) used for business purposes
• Modern examples
• BASIC (1964) used for regular folks to write
  easy programs
• C, C -- general purpose
• JAVA (1995) -- used as applets on web pages

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BASIC example displays room, patient name,
doctor name
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4th generation programming languages (4GL)

• First appeared in the1970s
• Languages designed with a specific purpose in
  mind such as the development of commercial
  business software.

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Some Different types of 4GLsin the 1970-1990 era

• Report generators PostScript
• Data manipulation analysis MAPPER, PL/SQL,
  SAS,
• Data Query Languages -- SQL
• Screen painters Oracle
• Web Development ColdFusion, CSS

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Is there a 5GL?

• Theres no agreed upon answer
• Some sources claim that thea 5GL language is
  programming that uses a visual or graphical
  development interface
• Other sources claim thatsystems used in the
  field of artificial intelligence, fuzzy logic,
  and neural networks are 5GL languages.

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High-Level Language (gt2GL)
Assembly Language (2GL)
Machine Language (1GL)
Hardware
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Quick Recap

• High level (3GL, 4GL)
• closer to human languages and further from
  machine languages
• Easier to understand, write, and maintain.
• Must be translated into machine language by a
  compiler or interpreter
• Low-level (2GL)
• very close to machine languages (2GL)
• Dependent on a certain type of hardware

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Programming Concepts
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Structured Programming

• A long time ago a man called Edsger Dijkstra came
  up with a concept called structured programming
  meaning that all programs could be structured in
  the following four ways

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1Sequences of Instructions

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2Branches
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3Loops
Repeated Steps
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4Modules
Shared Module
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Components that programs need..

• Data to work with..
• Operations (add, subtract, compare)
• Input/Output capability
• The ability to get data in
• The ability to get the results out

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Two perspectives of a program

• The one perceived by the user
• The user has an executable file and knows nothing
  about how it works it just does
• The user executes the program to perform a task
  (eg., a word processor, a video game, an image
  editor any software that can be installed
  executed)

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Two perspectives of a program

• The one perceived by the programmer
• The programmer has the source file that
  contains the instructions for the program.
• The instructions are written in some programming
  language
• At some point, the instructions get translated
  to an executable file
• The programmer needs to know exactly how it
  works..

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Translating High Level Languages to Machine Code

• The programmer generates the source code
• Recall that high level languages use a
  translation program to convert to machine code
  (also known as binary code or machine code)

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How does the translation process work?

• Source code must first be examined for
  grammatical errors. (If errors are found the
  translation stops)
• It is then translated into object code

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Two general types of translation processes

• an interpreter follows this iterative process for
  each line of the program
• checks for proper syntax
• translates the high-level instruction into
  machine code
• executes
• A compiler follows this process
• Checks for proper syntax across the entire
  program
• Then, translates the high-level instructions into
  machine code (across the entire program) and puts
  the result into an executable file
• (A user can then execute the file whenever
  desired)
• Fyi RealBasic is a compiled language..

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CLI Interface

• The first personal computers operated using a CLI
  (command line interface).
• Users would type commands directly into the
  computer to input or request output.

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GUI Interface

• A Graphical User Interface (GUI) is a user
  interface based on graphics (icons, pictures,
  menus). Users interact with the interface by
  directly manipulating the graphical elements
  (e.g., using a keyboard, mouse, joystick, touch
  screen, etc)
• The GUI is common to all modern applications
  written for the Unix/Linux/Apple and Windows
  environments.

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Programming in the GUI Environment

• When the GUI environment was in its early days,
  programmers found themselves spending countless
  hours writing instructions for typical GUI
  events
• To react to buttons being pressed, to work scroll
  bars, to communicate with dialog boxes, and to
  interact with menus
• This detracted from what programmers were really
  trying to achieve in their programs
• Tasks that used to take a few lines of program
  code now needed pages to comply with GUI
  Standards

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This led to object oriented environments

• In object-oriented/event-driven languages, the
  emphasis of a program was able to shift to the
  objects included in the user interface.
• All the handling needed behind the event, called
  the event handler, is already taken care of..
• e.g., Detection of events such as mouse rollover,
  mouse click, key press, text field change were
  already handled and didnt need to be coded by
  the programmer

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Where we are..

• C, C, Java, REALbasic, and Visual Basic are
  object-oriented/event-driven programming
  languages that are easy enough for a
  nonprogrammer to use, yet sophisticated enough to
  be used by professional programmers

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Next Steps

• Number system conversion
• well be investigating how to convert between the
  number system we use the number system
  computers use

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.. And after that

• Then with all of this great knowledge under our
  belts, well jump into RealBasic and start some
  programming!!!