1. Lecture II Basic computer and programming concepts
Yi Lin
Jan 09, 2007

2. 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 * * = ?
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COMP208 Computers in Engr

3. 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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COMP208 Computers in Engr

4. Computer Hardware Von Neumann model …… FETCH and EXECUTE storage
Command n
Command 2 ……
Von Neumann model
FETCH and EXECUTE
Command 1
Command n
storage
Command 2
storage
Command n ……
storage
Command n ……
Command 2
Monitor
results
processor
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5. Computer Hardware Keyboard Hard Disk Memory BUS Cache Register Monitor
Printer
Register
CPU
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6. The 5 Classic Components
Computer
CPU
Memory
Control
Input
Devices
Registers
Output
Devices
That is, any computer, no matter how primitive or advance, can be divided into five parts:
1. The input devices bring the data from the outside world into the computer.
2. These data are kept in the computer’s memory until ...
3. The datapath request and process them.
4. The operation of the datapath is controlled by the computer’s controller.
All the work done by the computer will NOT do us any good unless we can get the data back to the outside world.
5. Getting the data back to the outside world is the job of the output devices.
The most COMMON way to connect these 5 components together is to use a network of busses.
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7. Input / Ouput
Input
Output
Those are only the ones I came up with when I wrote this slide…
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COMP208 Computers in Engr

8. 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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9. Different natural languages
Wie geht es Ihnen?
How are you?
And more ……
Comment allez-vous?
你好吗？
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10. Different programming languages
C++ C# C
Assembly
(Intel8086, Motorola68000)
Machine language
And more ……
Fortran
Java
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11. Very high level language
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., )
Speed
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COMP208 Computers in Engr

12. 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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COMP208 Computers in Engr

13. 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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COMP208 Computers in Engr

14. 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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COMP208 Computers in Engr

15. 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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COMP208 Computers in Engr

16. 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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17. Let’s start A simplest Fortran program
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18. Hello World! Edit: 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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19. Hello World (cont.) Edit (open a scite editor) compile
Fortran  Machine Language
Scite menu: Tools->compile (Ctrl+F7)
Link (not necessary for simple programs)
Linking libraries used in the program
Run
Scite menu: Tools ->go (F5)
Output: “Hello World!”
Repeat
Until
succeed
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20. Hello World (cont.) PROGRaM hello IMPLIcIT NONE
Program name
block
PROGRaM hello
IMPLIcIT NONE
WRITE(*,*) "Hello World!"
END PROGRaM
Later
“!” comment
the whole line
WRITE(*,*): Write something on the screen
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21. 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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22. 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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23. 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!”
Note: These two facts only for codes, not for data
WRITE(*,*) “HELLO W O RLD !”
same
same
Different
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24. A simple example: Roots finding
Finding roots for quadratic
aX^2+bX+c=0
Input a, b, c
Output root(s):
(-b + SQRT(b*b - 4*a*c))/(2*a)
(-b - SQRT(b*b - 4*a*c))/(2*a)
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25. Roots finding (cont.) start Initialize a=1, b=-5, c=6
w = (b*b – 4*a*c)
R1 = (-b + sqrt(w))/(2*a)
R2 = (-b - sqrt(w))/(2*a)
End
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26. Roots finding (cont.) Declare variables, Must at the head of block
PROGRAM ROOTSFINDING
INTEGER a, b, c
REAL x, y, z, w, r1, r2
a=1
b=-5
c=6
! To calculate b*b – 4*a*c
x = b*b
y = a*c
z = 4*y
w = x-z
r1 = (-b +SQRT(w))/(2*a)
r2 = (-b – SQRT(w))/(2*a)
WRITE(*, *) r1, r2
END PROGRAM
Declare variables,
Must at the head of block
initialize variables with values
statements: calculation
statements:Output results
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COMP208 Computers in Engr

27. Roots finding (cont.) Keywords in Fortran90 variables constants
PROGRAM ROOTSFINDING
INTEGER a, b, c
REAL x, y, z, w, r1, r2
a=1
b=-5
c=6
! To calculate b*b – 4*a*c
x = b*b
y = a*c
z = 4*y
w = x-z
r1 = (-b +SQRT(w))/(2*a)
r2 = (-b –SQRT(w))/(2*a)
WRITE(*, *) r1, r2
END PROGRAM
variables
operators
constants
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28. 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
Don’t use keywords in Fortran as variables’ names
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COMP208 Computers in Engr

29. Variable data types E.g., a, b, c E.g., x, y, z, w
INTEGER
E.g., a, b, c
REAL
E.g., x, y, z, w
LOGICAL
COMPLEX
CHARACTER
Examples:
Data type is important
INTEGER::a=1,b=-5,c=5
INTEGER r1, r2
IMPLICIT NONE needed to prevent errors.
Comment out “IMPLICIT NONE”
write(*, *) r1, r3
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30. Declarations Declarations tell the compiler
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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31. Declare variables INTEGER:: a=1, b=-5, c=6 REAL:: x, y, z, w
same
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32. Variable precision 11111111 KIND BITs Value range 1 8
1 byte = 8 bits
INTEGER(KIND=2)::a OR INTEGER(2)::a
KIND
BITs
Value range 1 8
-2**7 < a < +2**7 (i.e., +128) 2 16
-2**15 < a < +2**15 (i.e., )
4(default) 32
-2**31 < a < +2**31 64
-2**63 < a < +2**63
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33. Variable precision (cont.)
REAL(KIND=4)
CHARACTER
KIND=1 only
KIND
BITs
4(default) 32
8(equivalent to DOUBLE PRECISION) 64 16
8*16
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COMP208 Computers in Engr