Programming

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Programming
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General Purpose

• The computer is a general purpose tool
• General purpose means it can do more than one
  thing
• How do we make it do more than one thing?
• make it perform a handful of small tasks that
  could be combined to perform more complicated
  tasks
• allow it to follow instructions to perform the
  above tasks
• It is programmable (i.e., we can program it)
• A computer program a list of instructions for
  the computer
• What sort of instructions does the computer
  understand?

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Tell me what to do. . .

• Make me a peanut butter and jelly sandwich
• What does this mean to you?

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Really tell me what to do. . .

• Go to the refrigerator
• Open fridge
• If ((no peanut butter) or (no jelly))
• Go to store and buy ingredients
• Remove peanut butter and jelly
• Get bread
• Open bread
• Do twice
• Take slice from bag
• Place slices side by side
• Get knife
• Open peanut butter jar
• Insert knife into jar
• Apply peanut butter to knife
• While surface of bread is not covered with peanut
  butter
• Apply peanut butter to bread from knife
• Close peanut butter jar
• Open jelly jar
• Insert knife into jar

simple tasks
logic
repetition
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Language of Instructions

• What do we need to know about the target of our
  instructions before we can give them?
• How do we ask them to do things?
• What do they know how to do?
• What language do they speak?

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Syntax and Grammar

• Syntax the form of what you say
• The grammatical structure (form) of a language
• Grammar defines the words you are allowed to use
  and specifies the order in which you can place
  them
• a grammar defines a syntax

the sandwich grammar
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Language of instructions

• Semantics the meaning of what is said
• Semantics explain how you interpret the results
  of parsing
• make is a verb
• A verb tells me what action to take
• peanut butter and jelly is an adjective
• An adjective tells me about a noun
• sandwich is a noun
• The noun is the target of my action
• The semantics provide the meaning for each of
  these things
• Ex when you encounter a make adjective sandwich
  you will need to get two pieces of bread, and put
  the adjective between the pieces of bread.
• How does this relate to computers?
• Beyond the obvious fact that in the future there
  will be robots and they will make us sandwiches

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Applied to Computers. . .

• What language does a computer speak ?
• Computers think in binary.
• Internally, they only understand 1s and 0s
• Weve learned that computers can do fancy things
  with 1s and 0s
• Boolean logic
• Mathematics
• Store and retrieve 1s and 0s
• We need the computer to know that a particular
  sequence of 1s and 0s uniquely identifies some
  task to do (semantics)
• We need to give the computer a series of 1s and
  0s
• Ideally we (humans) would like a mapping between
  English (or something closer to English) and
  something that makes sense to the computer
  (binary)

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In the beginning

• Early computers were primarily special purpose
  mathematic computers.
• Computers were designed to perform a particular
  arithmetic task or set of mathematic tasks.
• Computers that were unable to change their tasks
  are hardwired
• Hardwiring Using solder to create circuit boards
  with connections needed to perform a specific
  task (in a larger sense).
• Computers that were able to have their tasks
  changed required direct hardware modification
  by skilled engineers
• Change the flow of electricity to run through
  different logic paths
• Fat-fingering Engineer needed to position
  electrical relay switches manually.

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The Programming Language Continuum

• ENIAC
• Used programs to complete a number of different
  mathematical tasks.
• Programs were entered by plugging connector
  cables directly into sockets on a plug-in board.
• Set-up could take hours.
• A program would generally be used for weeks at a
  time.

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The Programming Language Continuum

• In the beginning To use a computer, you needed
  to know how to program it.
• Today People no longer need to know how to
  program in order to use the computer.
• In fact, programming has become easier as well
• programming languages evolve from low-level to
  high-level.
• Fifth Generation - Natural Languages
• Fourth Generation - Non-Procedural Languages
• Third Generation - People-Oriented Programming
  Languages
• Second Generation - Assembly Language
• First Generation - Machine Language (code)

High level
Low level
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Representing (Instructions) Programs

• Arithmetic Instructions
• Addition, subtraction, multiplication, division,
  and other numeric operations
• Data Movement Instructions
• Move numbers from place to place in the computer
• Logical or Comparison Instructions
• Decision making instructions e.g. x lt 10
• Control Instructions
• Controls the sequences in which instructions are
  executed e.g. for x 1 to 10
• Input/Output Instructions
• Allow the program to communicate with something
  outside the program (user, monitor, network,
  other programs)

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Representation of Programs
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Representation of Programs
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Generation I Machine Language

• Machine language programs made up of instructions
  written in binary code.
• Computers operate in their native language
• Humans translate their instructions into binary
• Each instruction has two parts Operation code,
  Operand
• Operation code (Opcode) The command part of a
  computer instruction.
• Operand The address of a specific location in
  the computers memory.
• You write programs in the lowest-level language
  directly for the CPU.
• Opcodes do very simple things (the computer is
  dumb) and you have it perform more complicated
  tasks by combining these instructions.

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Generation I Machine Language

• example . . .

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Generation I Machine Language

• Machine language
• Hardware dependent Could be performed by only
  one type of computer with a particular CPU.
• That is, each computer (although all speak
  binary) might have different arrangements of 1s
  and 0s for different instructions.
• Different words could have different meanings
• Maybe some computers cant do the same things
• 111 might be add to me, but 010 might be add to
  you..

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Generation IIAssembly

• Second Generation - Assembly Language
• Assembly language programs are made up of
  instructions written in mnemonics.
• Mnemonics Uses convenient alphabetic
  abbreviations to represent operation codes, and
  abstract symbols to represent operands.
• Each instruction (still) had two parts Operation
  code, Operand
• One-to-one mapping from written instruction to
  machine instruction
• Still a low-level language
• higher level languages
• Easier on the programmer

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The Programming Language Continuum

• Second Generation - Assembly Language
• Assembly language programs are made up of
  instructions written in mnemonics.
• Because programs are not written in 1s and 0s,
  the computer must first translate the program
  before it can be executed.
• The translation is a direct translation
• We translate into machine code
• READ OPCODE 001
• num1 Memory 0000 1110

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Assembled, Compiled, or Interpreted Languages

• Assembled languages
• Assembler a program used to translate Assembly
  language programs.
• Produces one line of binary code per original
  program statement.
• The entire program is assembled before the
  program is sent to the computer for execution.

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Generation III

• Third Generation High-level languages
• Instructions in these languages are called
  statements.
• High-level languages Use statements that
  resemble English phrases combined with mathematic
  and logical terms needed to express the problem
  or task being programmed.
• As before, programs are not written in 1s and 0s,
  the computer must first translate the program
  before it can be executed.
• Instructions are more complicated one may
  actually represent several simple opcodes
• NOT-Hardware dependent. portable
• So, as long as you can translate the statements
  from this language to another machine code, you
  can run it on that platform. (more on this
  later)

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High Level Language Example

• Pascal Example Read in two numbers, add them,
  and print them out.

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Generation IV

• Fourth Generation - Non-Procedural Languages
• Object-Oriented Languages A language that
  expresses a computer problem as a series of
  objects a system contains, the behaviors of those
  objects, and how the objects interact with each
  other.
• Object Any entity contained within a system.
• Examples
• A window on your screen.
• A list of names you wish to organize.
• An entity that is made up of individual parts.
• Objects pass messages, expose interfaces, can be
  inherited from other objects. . .
• Some popular examples C, Java, Smalltalk,
  Eiffel.

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O-O Language Example

• Object-Oriented Languages example (Simplified
  Java?)

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Generation V

• Fifth Generation - Natural Languages
• Natural-Language Languages that use ordinary
  conversation in ones own language.
• Research and experimentation toward this goal is
  being done.
• Intelligent compilers are now being developed to
  translate natural language (spoken) programs into
  structured machine-coded instructions that can be
  executed by computers.
• Effortless, error-free natural language programs
  are still some distance into the future.