Introduction to Computers and Programming 01204111 Computer Programming

Introduction to Computers and Programming 01204111 – Computer Programming

What is a computer? • A computer is a machine that Follows instructions (software) in memory Ø Reads input data Ø Stores and processes data Ø Produce outputs Ø 2

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 3

Types of computers • Desktop computers • Notebook computers • Mobile computers (Personal Digital Assistants, PDA) • Mainframes • Super computers Microcomputers 4

Hardware • Input devices • Output devices • Central Processing Unit (CPU) • Main memory • Storage 5

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. Ø To do so, you have to think carefully and describe your idea into instructions in the language that the machine can understand. 6

Basic Steps Problem analysis Program design Implementation Testing 7

Programming languages • Programming languages Low-level languages. e. g. , machine languages, assembly language Ø High-level language. e. g. , C, Pascal, Java, C#, Python Ø 8

Low-level languages • Instructions depend on the specific architecture of the machines Ø E. g. , x 86, ARM, AVR architectures • Each instruction correspond to specific cycle of execution • A program written for a specific architecture cannot be executed in another architecture. 9

Low-level languages • Machine languages Ready to be executed Ø Usually written as binary or hexadecimal numbers Ø • Assembly language Encoded machine languages Ø Each instruction corresponds to one machine instruction. 00011000 01101011 00011001 11111100 10011000 11100000 รหสฐานสอง 18 6 B 19 FC 98 E 0 รหสฐานสบหก Ø SUB R 3, #2, R 6 01 011 110 00000010 10

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); 11

Example of high-level languages • Procedural Fortran Ø Cobol Ø Basic Ø C Ø Pascal Ø • Functional Ø Lisp • Object-oriented C++ Ø Java Ø C# Ø VB Ø • Logic Ø Prolog 12

Program Execution • A computer does not "understand" high-level languages. • To execute program in these languages, you need either: An interpreter Ø A compiler Ø 13

Interpreters • An interpreter reads each high-level language instruction and executes that instruction, one by one. ������ prog. bas �������� 14

Compilers • A compiler reads the whole program and translate it into machine readable instructions. ������ prog. c �����prog. exe ���������� 15

Languages used in this course • Python An interpretative language Ø Can be used on many computing systems (e. g. , on MS Windows, Unix, and even some mobile phones. ( Ø • C# A compilation language Ø More restrictive syntax Ø Very good for developing GUI applications Ø 16

Python • Is a multi-paradigm programming language Procedural Ø Functional Ø Object-oriented Ø • Is an interpretative language • Easy to get started • Very rich standard library 17

Installation • Download Python 3. 1 at Ø http: //www. python. org/ftp/python/3. 1. 2/python 3. 1. 2. msi • After the installation, you can try calling the Python Shell from the Start Menu. 18

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!") 19

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!" 20

Interaction with Python A "prompt" that shows that the system is ready to take commands 21

Try this • Try these commands (Don't type (<<< and observe the output >>> >>> >>> print(1) print(3*8) print("Hello") input() exit() 22

Combining instructions into programs • We can combine many instructions into a single program for ease of usage later on. Each instruction are executed in order from top to bottom. Ø We call this sequence of instructions "a program". Ø • 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 23

Traditional program development cycle input Editor prog. py program The development process gets much simplified with the use of IDE's. We shall talk about a particular IDE on the next few slides. Python output 24

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. Ø By adding a command" input()", you can keep the window opened. 25

Wing IDE 101 • In this course, we will develop programs in an Integrated Development Environment (IDE) It has a build-in editor Ø Can execute programs inside the system Ø It comes with a debugging tool. Ø 26

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 * 27

What can a turtle do? • Moves forward/backward • Turns left or right • Takes a pen with it 28

Basic turtle control – 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 • t = Turtle() 29

Tell the turtle to draw a square • In English: Walk Turn for 100 steps right 90 degree 30

Tell the turtle to draw a square • In Python: from turtle import * t = Turtle() t. forward(100) t. right(90) t. forward(100) 31

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) square() 32

Repetitive instructions • The instructions are very repetitive. • High-level languages have ways to reduce this instruction repetition and duplication Ø 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() 33

Thinking Corner • Write a program that tells the turtle to draw a equilateral triangle whose sides are 200 -step long, on the canvas. 34

Software required for the first half • Python 3. 1. 2 Ø http: //python. org/ftp/python/3. 1. 2/python-3. 1. 2. msi • Wing IDE 101 Ø Ø An integrated development environment for Python http: //wingware. com/pub/wingide-101/3. 2. 5/wingide-101 -3. 2. 5 -1. exe 35