Transcript 01-Intro

Introduction to Computers
and Programming
01204111 – Computer Programming
What is a computer?
• A computer is a machine that
Follows instructions (software) in memory
 Reads input data
 Stores and processes data
 Produce outputs

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Development
• Abacus
• Analytical Engine
• 1 Generation (1940-1956): Vacuum Tubes
• 2 Generation (1956-1963): Transisters
• 3 Generation (1964-1971): Integrated Circuits
• 4 Generation (1971-Present): Microprocessors,
VLSI/ULSI
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Types of computers
• Desktop computers
• Notebook computers
• Mobile computers
(Personal Digital Assistants, PDA)
• Mainframes
• Super computers
Microcomputers
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Hardware
• Input devices
• Output devices
• Central Processing Unit (CPU)
• Main memory
• Storage
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Computer Programming
• To program a computer is to write instructions so
that the computer can complete the required task.
• These instructions must be specific and unambiguous.

To do so, you have to think carefully and describe your
idea into instructions in the language that the machine
can understand.
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Basic Steps
Problem analysis
Program design
Implementation
Testing
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Programming languages
• Programming languages
Low-level languages. e.g., machine languages, assembly
language
 High-level language. e.g., C, Pascal, Java, C#, Python
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Low-level languages
• Instructions depend on the specific architecture of the
machines
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E.g., x86, ARM, AVR architectures
• Each instruction correspond to specific cycle of
execution
• A program written for a specific architecture cannot
be executed in another architecture.
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Low-level languages
• Machine languages


Ready to be executed
Usually written as binary or
hexadecimal numbers
00011000 01101011
00011001 11111100
10011000 11100000
รหัสฐานสอง
18 6B 19 FC 98 E0
• Assembly language


Encoded machine languages
Each instruction corresponds to one
machine instruction.
รหัสฐานสิบหก
SUB
R3, #2, R6
01 011 110 00000010
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High-level languages
• Read more naturally
• Are usually independent of the underlying
architecture. -> More portable
• Each statement may correspond to many machine
instructions
SUM := A * 2 + ALPHA/3;
PRINTLN(SUM);
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Example of high-level languages
• Procedural

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Fortran
Cobol
Basic
C
Pascal
• Functional

• Object-oriented
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C++
Java
C#
VB
• Logic
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Prolog
Lisp
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Program Execution
• A computer does not "understand" high-level
languages.
• To execute program in these languages, you need
either:
An interpreter
 A compiler
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Interpreters
• An interpreter reads each high-level
language instruction and executes
that instruction, one by one.
prog.bas
ซอร์สโค้ด
อินพุท
อินเทอร์พรีเตอร์
เอาท์พุท
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Compilers
• A compiler reads the whole program
and translate it into machine readable
instructions.
prog.c
ซอร์สโค้ด
คอมไพเลอร์
อินพุท
prog.exe
รหัสภาษาเครื่อง
เอาท์พุท
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Languages used in this course
• Python
An interpretative language
 Can be used on many computing systems (e.g., on MS
Windows, Unix, and even some mobile phones).

• C#
A compilation language
 More restrictive syntax
 Very good for developing GUI applications
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Python
• Is a multi-paradigm programming language
Procedural
 Functional
 Object-oriented
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• Is an interpretative language
• Easy to get started
• Very rich standard library
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Installation
• Download Python 3.1 at

http://www.python.org/ftp/python/3.1.2/python3.1.2.msi
• After the installation, you can try calling the Python
Shell from the Start Menu.
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Thinking Corners
• Try to guess what the following program is doing.
1: print("Welcome")
2: g = input("Guess the number: ")
3: guess = int(g)
4: if guess == 5:
5:
print("You win!")
6: else:
7:
print("You lose!")
8: print("Game over!")
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Natural languages
• A program is not that different from human natural
language
1: Display "Welcome"
2: Let g be input("Guess the number: ")
3: Let guess be int(g)
4: if guess equals 5:
5:
Display "You win!"
6: else:
7:
Display "You lose!"
8: Display "Game over!"
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Interaction with Python
A "prompt" that
shows that the
system is ready to
take commands
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Try this
• Try these commands (Don't type >>>) and observe
the output
>>>
>>>
>>>
>>>
>>>
print(1)
print(3*8)
print("Hello")
input()
exit()
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Combining instructions into programs
• We can combine many instructions into a
single program for ease of usage later on.
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Each instruction are executed in order from
top to bottom.
We call this sequence of instructions "a
program".
• You can use any editing software to create
this program file, e.g., Notepad.
• Python programs's names end with .py
,e.g., first.py
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Traditional program development cycle
input
Editor
prog.py
program
Python
output
The development process gets much simplified
with the use of IDE's.
We shall talk about a particular IDE on the next few slides.
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How to run your program
• You can double-click at the .py file. The Python
interpreter will start to execute your program.
• Notes: After the program finishes, the window will
be closed immediately.

By adding a command "input()", you can keep the
window opened.
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Wing IDE 101
• In this course, we will develop programs in an
Integrated Development Environment (IDE)
It has a build-in editor
 Can execute programs inside
the system
 It comes with a debugging
tool.
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Turtle-style graphics
• We shall learn basic ideas of programming by telling
and teaching turtles to draw.
• From the Python Shell we can start using the Turtle
graphics system by typing
from turtle import *
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What can a turtle do?
• Moves forward/backward
• Turns left or right
• Takes a pen with it
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Basic turtle control
• t = Turtle()
– Create a turtle, call it t
• t.forward(d) - tell t to walk d steps
• t.backward(d) - tell t to walk backwards d for steps
• t.right(a) - tell t to turn right for a degree
• t.left(a) - tell t to turn left for a degree
• t.penup() – tell t to lift the pen up from the canvas
• t.pendown() - tell t to put the pen back to the canvas
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Tell the turtle to draw a square
• In English:
Walk
Turn
Walk
Turn
Walk
Turn
Walk
Turn
for 100 steps
right 90 degree
for 100 steps
right 90 degree
for 100 steps
right 90 degree
for 100 steps
right 90 degree
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Tell the turtle to draw a square
• In Python:
from turtle import *
t = Turtle()
t.forward(100)
t.right(90)
t.forward(100)
t.right(90)
t.forward(100)
t.right(90)
t.forward(100)
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Teach the turtle
• You can define new commands using def
from turtle import *
t = Turtle()
Make sure the
indentation is
aligned.
def square():
t.forward(100)
t.right(90)
t.forward(100)
t.right(90)
t.forward(100)
t.right(90)
t.forward(100)
t.right(90)
square()
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Repetitive instructions
• The instructions are very repetitive.
• High-level languages have ways to reduce this
instruction repetition and duplication
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To reduce program complexity and increase readability.
from turtle import *
t = Turtle()
def square():
for x in range(4):
t.forward(100)
t.right(90)
square()
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Thinking Corner
• Write a program that tells the turtle to draw a
equilateral triangle whose sides are 200-step long,
on the canvas.
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Software required for the first half
• Python 3.1.2
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http://python.org/ftp/python/3.1.2/python-3.1.2.msi
• Wing IDE 101
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An integrated development environment for Python
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http://wingware.com/pub/wingide-101/3.2.5/wingide-101-3.2.5-1.exe
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