Introduction to Computing and Programming

1
Introduction to Computingand Programming
Notes adapted from Introduction to Computing and
Programming with Java A Multimedia Approach by
M. Guzdial and B. Ericson, andinstructor
materials prepared by B. Ericson.
2
Learning Goals

• Understand at a conceptual level
• What is a computer?
• What is in a traditional computer?
• What is a program?
• What is programming all about?
• Why learn to program?

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What is a Computer?

• A device that performs high-speed mathematical
  and/or logical operations or that assembles,
  stores, correlates, or otherwise processes
  information.
• The first computers were people
• who did computations

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What is a Computer?

• By this standard, a lot of things can be
  considered to be computers as well.
• Some devices are pretty old (like the abacus)
• Others are brand new or are emerging on the
  horizon (like the DNA computer)

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What is in a Traditional Computer?

• Central Processing Unit (CPU) (also known as
  the processor)
• Executes instructions.
• Main Memory (also known as RAM)
• Internal storage that holds the programs
  (instructions and data) currently being executed
  by the CPU.
• Memory is made up of electronic on-off
  switches, each of which represents 0 or 1 and is
  called a bit (binary digit)
• Main memory is volatile (information stored in it
  is not retained when power is discontinued).

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What is in a Traditional Computer?

• Secondary Memory diskettes, hard disks, CDs,
  DVDs, USB sticks
• Provide long-term (persistent) storage for
  programs and other information.
• Organized as files each of which has a file
  name and a folder or directorythat contains it.
• Input/Output (I/O) units keyboard, mouse,
  screen, printer, webcam,
• Used for communicating information from the user
  to the computer and the computer to the user.

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What is in a Traditional Computer?
Memory
Output Devices
Input Devices
Central
Processing Unit
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What is Programming?

• Creating detailed instructions that a computer
  can execute to accomplish some task.
• Like writing a recipe for your favorite dish
• Or giving someone directions to your house
• Or making a robot do what you want

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What is Programming?

• The end product of programming is, naturally, a
  program.
• Programs consist of
• Statements instructions to perform the task.
• Data a collection of variables.
• Variable a named storage area in the computers
  memory that holds data required for the task!

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Early Programming

• Early computers required the programmer to set
  switches and move wires
• Which represented a series of 0s and 1s
• Later computers were programmed using punched
  cards
• Again, still a series of0s and 1s

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Language Evolution

• Early languages were based on how to do
  instructions on each different machine
• 0s and 1s to add, subtract, read, store, etc.
• Consequently, these languages were called
  machine languages
• The (usually small) set of instructions that the
  computers CPU can execute directly.
• Machine dependant the hardware designers
  decide on the machine language instruction set.
• Difficult for programmers to use although the
  first computers were programmed only using
  machine language!
• Example

000100111000010100100110101111001
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Language Evolution

• After this came assembly language
• Introduced to make the programmers task easier.
• Mnemonic representation of machine language.
• Therefore, it is also machine dependent.
• Assembly language program segment example
• Need an assembler software that translates
  assembly language programs into machine language.
• Recall for a computer to execute a program, it
  must be in the machine language for that type of
  computer.
• One to one correspondence exists between assembly
  language instructions and machine language
  instructions.

LOAD R1, PRICELOAD R2, TAXADD R1, R2, R6STOR
R6, TOTAL
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Language Evolution

• Next came the high-level language
• Created to help programmers more easily write
  correct programs that perform complicated tasks.
• One to many correspondence exists between
  high-level language instructions and machine
  language instructions thus, high-level languages
  are said to be more powerful than assembly
  languages.
• High-level language program segment example

if ((numberOfStudents) gt MAX_STUDENTS)
fullCourse true
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Language Evolution

• More on high-level languages
• Need a compiler software that translates
  high-level language programs into machine
  language.
• Machine-independent high-level languages are
  not designed with a particular type of computer
  in mind.
• i.e. a program written in C can be executed on
  many different types of computers (e.g. PC,
  Macintosh) once we have a C compiler for that
  type of machine.
• A couple of terms
• Source code a program written in a high-level
  language (e.g. Java, C, Pascal).
• Executable (or binary) code a program that has
  been translated (usually by an assembler or
  compiler) into machine language code.

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Which Language?

• High-level languages are eventually translated
  into machine language
• You can write the same program in essentially any
  language
• The computer doesnt care what high-level
  language you use, because it is eventually given
  the machine language
• The language matters to the programmer
• How easy is it to learn the language?
• How long does it take to write the program?
• How hard is it to change the program?
• How long does it take to execute?

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Java

• A high-level language developed by Sun
  Microsystems in the early 1990s
• Cross-platform, object-oriented language
• Includes the advantages of previous programming
  languages while excluding many of the
  disadvantages hopefully!
• Used in business, science, and education
• One of the fastest adopted technologies of all
  time

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Java

• Java source code to machine language
• Different from previous high-level languages.
• Java is compiled but, not directly into machine
  language like its predecessors, rather into an
  intermediate language called Java bytecode.
• Java bytecode is machine independent.
• The Java interpreter (aka Java Virtual Machine)
  then translates and executes the bytecode on the
  computer, one bytecode instruction at a time.
• Java compilers that compile down to machine
  language directly are available, but are not the
  norm.
• Why does Java do it this way?
• Portability create compiler once then create an
  interpreter for each machine. (An interpreter is
  easier to create than a compiler )

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Why Dont We Just Use English?

• English is good for communication between two
  intelligent humans
• Even then we sometimes dont understand
• Computers are very stupid
• They basically know how to add, compare, store,
  and load
• Programs are very detailed instructions
• Everything must be precise and unambiguous

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Programming Exercise

• Write down instructions for how to make a
  sandwich
• Have someone else read the directions and do the
  actions literally, precisely as they were written
  
• stop anytime anything isnt clear and ask for
  clarification
• It isnt that easy, is it?

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Why Learn to Program?

• Alan Perlis, first head of Carnegie Mellon's
  Computer Science Department, made the claim in
  1961 that computer science, and programming
  explicitly, should be part of a liberal education
• Seymour Papert claimed in the 70s and 80s that
  learning to program is learning to think, and
  debug ones own thoughts.
• If you learned to program, you learned to plan,
  to debug, to handle complexity, and so on.

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Why Learn to Program?

• The computer is the most amazingly creative
  device that humans have ever conceived of. If you
  can imagine it, you can make it real on a
  computer.
• Computers will continue to have a major impact
  on modern life
• Movies, games, business, healthcare, science,
  education, etc.

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Computers are Commonplace

• Computers, or at least processors, are in many
  common devices

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Programming is Communicating

• Alan Perlis, You think you know when you can
  learn, are more sure when you can write, even
  more when you can teach, but certain when you can
  program.

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Summary

• Computers are fairly simple machines
• Fancy calculators with lots of storage
• But incredibly fast
• Computers have changed modern life
• Programs are instructions to a computer to
  accomplish a task
• Programs written in high-level languages must
  somehow be translated to machine language for
  execution
• Programming can be tricky to learn
• But there are some ways to make it easier