Lecture II Basic computer and programming concepts

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Lecture II Basic computer and programming concepts

• Yi Lin
• Jan 09, 2007

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What is computer?

• Computers are clever idiots
• Idiot Do whatever it is ordered
• Clever But fast and never wrong.
• Who gives the orders?
• Programmers
• In what forms?
• Programs in certain syntaxes (i.e., in certain
  programming languages)

34253 98573 15462 ?
52206221022678
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Computer
Windows XP, Linux, Microsoft Office, Internet
Browser
Software
Pentium 4 CPU, AMD, 512 MB DDR memory, 19 inch
LCD, Keyboard,
Hardward
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Computer Hardware

• Von Neumann model
• FETCH and EXECUTE

Command 1
processor
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Computer Hardware
Keyboard
Hard Disk
Memory
BUS
Monitor Printer
Cache
Register
CPU
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The 5 Classic Components
Computer
CPU
Memory
Control
Input Devices
Registers
Output Devices
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Input / Ouput
Output
Input
Those are only the ones I came up with when I
wrote this slide
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Computer Software (program)

• A program is a set of step-by-step instructions
  that directs the computer to do the tasks you
  want it to do and produce the results you want.
  In what form?
• E.g., Windows XP, Red hat, Microsoft Office
  (Word, PowerPoint, Excel), Computer Virus
• Showing a few example programs, BallGame,
  TypingGame,

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Different natural languages
Wie geht es Ihnen?
How are you?
And more
Comment allez-vous?
????
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Different programming languages
C
C
C
Assembly (Intel8086, Motorola68000)
Machine language
And more
Fortran
Java
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Levels of language
Natural language
Easiness for human, i.e., more flexibility,
easier to be implemented, maintained
Very high level language (e.g., Java, C, SQL)
High level language (e.g., Fortran, C, Cobol)
Assembly language (Intel 8086, Motorola 68000,
Sun Sparc)
Machine Language (e.g., 01001110000)
Speed
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Choosing a language

• Manager choices a language for everyone in the
  group
• Suitable for your tasks
• Satellite communication (speed) ?Assembly
• Education ?Basic, Pascal
• Business ? Cobol
• Web development ?Javascript, Java
• Scientific calculation ?Fortran
• Real programmer in general purpose ?C

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Major programming language Fortran

• The First High-Level Language
• Developed by IBM and introduced in 1957
• Primarily associated with engineering,
  mathematical, and scientific research tasks.
• Rich in math library

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Major programming language COBOL

• The Language of Business
• Although Fortran in 1950s, no high level language
  for business..
• The U.S. Department of Defense
  CODASYL-COnference of DAta SYstem Languages.
• 1959 COBOL-COmmon Business Oriented Language.
• 1974, American National Standards Institute
  ANSI-COBOL
• 1985, COBOL 85
• COBOL is very good for processing large files and
  performing relatively simple business
  calculations, such as payroll or interest.
• English-like-far more than FORTRAN or BASIC

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Major programming language Basic

• For Beginners and Others
• BASIC-Beginners' All-purpose Symbolic Instruction
  Code
• Developed at Dartmouth College by John Kemeny and
  Thomas Kurtz in 1965 and originally intended for
  use by students.
• For many years, BASIC was looked down on by "real
  programmers," who complained that it had too many
  limitations and was not suitable for complex
  tasks. Newer versions, such as Microsofts
  QuickBASIC, include substantial improvements.

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Major programming language C

• A language invented by Dennis Ritchie at Bell
  Labs in 1972
• Advantage
• C very fast assembly language while still
  offering high-level language features.
• Disadvantage
• Although C is simple and elegant, it is not
  simple to learn.
• C was originally designed to write systems
  software but is now considered a general-purpose
  language.
• The availability of C on personal computers has
  greatly enhanced the value of personal computers
  for budding software entrepreneurs.

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Lets startA simplest Fortran program
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Hello World!
PROGRaM hello IMPLIcIT NONE WRITE(,) "Hello
World!" END PROGRaM
HelloWorld.f90

• Edit
• any text editor, e.g., SciTE, Notepad,
• Or IDE (Integrated Development Environment),
  e.g., Visual Fortran

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Hello World (cont.)

• Edit (open a scite editor)
• compile
• Fortran ? Machine Language
• Scite menu Tools-gtcompile (CtrlF7)
• Link (not necessary for simple programs)
• Linking libraries used in the program
• Run
• Scite menu Tools -gtgo (F5)
• Output Hello World!

Repeat Until succeed
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Hello World (cont.)

• PROGRaM hello
• IMPLIcIT NONE
• WRITE(,) "Hello World!"
• END PROGRaM

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The Program Block

• PROGRAM hello
• IMPLICIT NONE
• !This is my first program
• WRITE (,) Hello World!
• END PROGRAM hello
• The bold keywords tell the compiler where the
  program begins and ends.
• They bracket a section of code called a block
• Using uppercase is a convention to distinguish
  keywords.
• FORTRAN is case insensitive. PROGRAM, program,
  proGRAM, pRoGrAm are all the same.

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The Program Block in General

• Syntax for the program block
• PROGRAM program-name
• IMPLICIT NONE
• declarations
• statements
• subprograms
• END PROGRAM program-name

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Some specific facts about codes

• White space insensitive
• WRITE(,) Hello world!
• WRITE (, ) Hello world!
• W RITE(,) Hello world! ? compile error
• case insensitive
• WRITE(,) Hello world!
• write(,) Hello world!
• Note These two facts only for codes, not for
  data
• WRITE(,) Hello world!
• WRITE(,) HELLO W O RLD !

same
same
Different
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A simple example Roots finding

• Finding roots for quadratic
• aX2bXc0
• Input a, b, c
• Output root(s)
• (-b SQRT(bb - 4ac))/(2a)
• (-b - SQRT(bb - 4ac))/(2a)

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Roots finding (cont.)
start
Initialize a1, b-5, c6
w (bb 4ac)
R1 (-b sqrt(w))/(2a) R2 (-b -
sqrt(w))/(2a)
End
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Roots finding (cont.)

• PROGRAM ROOTSFINDING
• INTEGER a, b, c
• REAL x, y, z, w, r1, r2
• a1
• b-5
• c6
• ! To calculate bb 4ac
• x bb
• y ac
• z 4y
• w x-z
• r1 (-b SQRT(w))/(2a)
• r2 (-b SQRT(w))/(2a)
• WRITE(, ) r1, r2
• END PROGRAM

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Roots finding (cont.)

• PROGRAM ROOTSFINDING
• INTEGER a, b, c
• REAL x, y, z, w, r1, r2
• a1
• b-5
• c6
• ! To calculate bb 4ac
• x bb
• y ac
• z 4y
• w x-z
• r1 (-b SQRT(w))/(2a)
• r2 (-b SQRT(w))/(2a)
• WRITE(, ) r1, r2
• END PROGRAM

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Variables and constants

• Constants (e.g., 1, -5, 6, 4, 2)
• A variable (e.g., a, b, c, x, y, z, w) is a
  unique name which a FORTRAN program applies to a
  word of memory and uses to refer to it.
• Naming convention
• alphanumeric characters (letters, numerals and
  the underscore character)
• The first character must be a letter.
• No case sensitivity
• Dont use keywords in Fortran as variables names

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Variable data types

• INTEGER
• E.g., a, b, c
• REAL
• E.g., x, y, z, w
• LOGICAL
• COMPLEX
• CHARACTER
• Examples
• Data type is important
• INTEGERa1,b-5,c5
• INTEGER r1, r2
• IMPLICIT NONE needed to prevent errors.
• Comment out IMPLICIT NONE
• write(, ) r1, r3

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Declarations

• PROGRAM RootFinding
• IMPLICIT NONE
• INTEGER a, b, c
• REAL x,y,z,w
• REAL r1, r2
• . . .
• END PROGRAM RootFinding
• Declarations tell the compiler
• To allocate space in memory for a variable
• What shape the memory cell should be (i.e. what
  type of value is to be placed there)
• What name we will use to refer to that cell

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Declare variables

• INTEGER a, b, c
• REAL x, y, z, w
• A1
• B-5
• C6

same
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Variable precision
1 byte 8 bits

• INTEGER(KIND2)a OR INTEGER(2)a

11111111
KIND BITs Value range
1 8 -27 lt a lt 27 (i.e., 128)
2 16 -215 lt a lt 215 (i.e., 32767)
4(default) 32 -231 lt a lt 231
8 64 -263 lt a lt 263
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Variable precision (cont.)
KIND BITs
4(default) 32
8(equivalent to DOUBLE PRECISION) 64
16 816

• REAL(KIND4)
• CHARACTER
• KIND1 only