KIT001 Programming Preparation Dr. Erin Roehrer

Lecture Two: Why Program? Introductory Programming Concepts

Reminders for this week

PUBLIC HOLIDAY Monday 9th of March 2015 This means there is NO lecture next Monday. Lecture is rescheduled for Thursday,

12th of March at 9am. Same locaQon but will only run for one hour.

Lab Classes/Tutorials commence next week, no labs classes on Monday due to public holiday. Monday classes are now Tuesday 1pm.

CIS accounts, lab access have you sorted this?

Lecture Objectives

CompuQng Tools and Terms

Why program?

What is a programming language?

Programming Tools and Terms

What is Python?

Using Python

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Computing Tools & Terms

Components of a computer

How those components interact

How computers store and manipulate information

Operating System

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Hardware & Software

Hardware Physical, tangible parts of a computer

keyboard, monitor, wires, chips

Software programs and data

a program is a series of instructions data is what the program instructs the computer to

manipulate (numbers, words etc)

A computer requires both hardware and software

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Hardware CPU and Main Memory

Central!Processing!

Unit"

Main!Memory!

Chip that executes program commands

Primary storage area for programs and data that

are in acQve use

CPU interacts with main memory

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Hardware Secondary Memory Devices

Main!Memory!

Central!Processing!

Unit!

Secondary memory devices provide long-term storage

InformaQon is moved between main memory and secondary memory as needed

USB Disk!

Hard Disk!

DVD/CD!

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Typical Hardware Conguration Monitor!

Keyboard!

Main!Memory!

Central!Processing!

Unit!

I/O (Input Output) devices for communicaQon with CPU

USB Disk!

Hard Disk!

DVD/CD!

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The Central Processing Unit (CPU) A CPU is also called a microprocessor or core

It/they conQnuously follow(s) the fetch-decode-execute cycle:

fetch!

Retrieve an instrucQon from main memory

decode!Determine what the instrucQon is

execute!Carry out the instrucQon - access and modify data if instructed to

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Software Categories

Operating System controls all machine activities user interface to the computer manages resources such as the CPU and memory Files Programs e.g. editor, compiler

Application program (App) generic term for any other kind of software we will write applications

Graphical user interface (GUI) some of our programs will have a GUI

Applications

UlQmately, any applicaQon we create will interact (successfully or unsuccessfully) with the computer and the data it contains.

Any applicaQon manipulates data in some way. Create Read Update Delete

How computers store data

All data that is stored within a computer is converted to 0s and 1s

The data is stored in the computers memory

The memory is divided into storage locaQons known as bytes

Le[er, numbers, and symbols are stored as binary numbers (combinaQons of 0s and 1s)

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Memory

Main memory is divided into many memory locaQons (or cells)

9278 9279 9280 9281 9282 9283 9284 9285 9286

Each memory cell has a numeric address, which uniquely idenQes it, o^en these are numbers in hexadecimal, e.g. 9a3f

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Storing Information

9278!9279!9280!9281!9282!9283!9284!9285!9286!

Large values are stored in consecuQve memory locaQons

10011010!Each memory cell stores a set number of bits (usually 8 bits, or one byte) called a word

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Storing Information 9278!9279!9280!9281!9282!9283!9284!9285!9286!

10011010!

To help us remember where a value is, memory locaQons can be given a name (idenQer)

firstName!rstName is called a variable.

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Storing Information 9278!9279!9280!9281!9282!9283!9284!9285!9286!

10011010!

To help us understand the value, variables are associated with a type

firstName (String)!rstName is a variable of type String.

Why Program?

Computers are very fast, but stupid machines

Things that humans might nd hard, or boring, computers are actually good at

Relevant to most elds of experQse: Recording Data Analysing Data Finding Pa[erns Plobng Data

AutomaQng Tasks Comparing Data MulQ-Tasking Image Processing

Why Program?

As such computer programs are used not only in our leisure time with games and social networks, but also in: Biology, Chemistry, Physics, Bioinformatics Commerce, Health, Industry Sociology, Law, Media Production

Basically computers are used in every field, and often programs are written by people whose main field of expertise is not computer programming

Why Program?

To create successful applicaQons that contain procedures so the computer can communicate with us and know what we want it to do!

What is a Programming Language

A programming language specifies words and symbols that can be used to write a program rules to form valid program statements

Source code (text) written by programmer Can just be typed into the editor and run; or can be stored in a

file A program usually consists of one or more classes; Classes

consist of one or more functions; Functions consist of one or more statements

Types of Programming Languages

Machine Language

Assembly Language (Low Level Language)

High-level Programming Language

Machine Languages

Machine Language A computers naQve language a set of primiQve

instrucQons. In the form of binary code

E.g.: 1101101010011010

Assembly Languages

Programming in Machine Language is tedious!

Assembly Language was created to make life a bit easier.

Uses a short descripQve words, mnemonic, to represent each of the machine language instrucQons.

Add 2, 3, result

High-Level Language

English-like

Easier to learn and use than assembly language

InstrucQons in high-level language are called statements

High level languages are called source code and need to be translated using another programming tool called an interpreter or a compiler.

High-Level Languages

Pascal

C

Visual Basic

Java

C++

C#

Python

Programming Tools & Terms

Syntax

Semantics

Structure of a program

Program development cycle

Syntax and Semantics

A program will only run if it follows EXACTLY the rules of the language (syntax)

syntax rules of a language dene how symbols, reserved words, and idenQers may be put together to make a valid program

A program will always do what we tell it to do, not what we MEANT to tell it to do (semanQcs)

semanQcs of a program statement dene what that statement means (what it will do when executed)

A program that is syntacQcally correct is not necessarily logically (semanQcally) correct

Structure of a program

Think of wriQng a le[er or email:

A wri[en language species words and punctuaQon that can be used to write a le[er rules to form understandable and recognisable

statements whitespace doesnt change the meaning of the le[er

Paper/Email contains the le[er Consists of secQons (salutaQon, subject, body, signature) Body consists of paragraphs; Paragraphs consist of

sentences

Re: My recent dummy-spit Dear Mummy, I am writing because I cannot find my teddy. It was sitting next to my beer, and I can no longer find it. If you have stolen it, could you please return it? The other guys in the regiment all have theirs Thanks. Sincerely, your loving son Mikey.

Components of a program

IdenQers Rules le[ers, numbers, and underscore (_) only and

cannot be the same as reserved words ConvenQons start with a le[er, examples later

Comments # rest of line is comment ''' everything is comment up

to '''

White Space (space, tab, blank lines) Blocks must be indented evenly Statements end with a new line ( key) Reserved words

Some languages Use syntax to collect statements into blocks, e.g. {} but

Python just uses alignment Use syntax to separate statements, e.g. ; but Python can

just use the end of line

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block !containing!code

# declarations # executable statements # and/or comments

Structure of a Program

Statements

print("Hello World!")

print("Programming is fun!")

Programming Style & Documentation

Appropriate Comments

Proper IndentaQon and Spacing

The Program Development Cycle

Design the program

Write the code

Correct syntax errors

Test the program

Correct logic errors

What is Python? Developed by Guido van Rossum in 1991. Python is a high-level general-purpose programming language that can be applied to many dierent classes of problems. With Python, students can be quickly introduced to basic concepts required for successful programming.

Easy to read Less development Qme (shorter code) Reduced learning Qme

What is Python?

Complied Directly converted to machine code

Interpreted Purely Interpreted

Directly converted to byte code

Indirectly converted to byte code

C, C++ Java, C# Python Shell, Perl

Who uses python?

On-line games

Web services

ApplicaQons

Science

Instrument Control

Embedded Systems

Pythons Reserved Words

and as assert break class continue def del elif

else except exec finally for from global if import

in is lambda not or pass print raise return

try while with yield

When we dont follow the rules.

Three types of errors Problems with syntax (compiler errors)

No execuQon or executable program produced

Problems during program execuQon (run-Qme errors) e.g. divide by zero, wrong sort of input program terminates abnormally

Problem with semanDcs (logical errors) program runs, but produces incorrect results

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PRINT("Hello World!")

Syntax Error Python is case sensitive

Find the error

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print("program over") print("program begins")

Semantic error - message "program over" will appear before message "program begins"

Find the error

Using Python

We want to launch the IDLE Python 2.7 programming environment from the Start Menu. All Programs Development Tools Python 2.7

IDLE (Python GUI) Or search for Python

Python 2 vs Python 3

Python 3 is a newer version, but it is not backward compaQble with Python 2. That means if you write a program using Python 2, it may not work on Python 3.

The Command Line

A First Python Statement

Understanding the Integrated DeveLopment Environment (IDLE)

You can create any Python applicaQon you want using just a text editor however there are InteracQve Development Environments (IDEs) that can make the process easier.

IDLE is the IDE that comes with Python.

IDLE provides the funcQonality to: Write Python Code Perform simple and code-based ediQng Save and Open Python (lename.py) les Perform simple debugging task, and more.

Creating your rst application

Creating a le

Running your application

Python on your own device

Python works on a number of platorms (combinaQon of computer hardware and operaQng systems so^ware).

To get the right version visit: h[p://www.python.org/download/ (you will need to scroll down to the download secQon). Most Mac computers will already have Python installed.

We are using version 2.7 in the compuQng labs

The Record Book

Contents any paper other than copies of text books Printed notes (lecture and tutorial) Your additional notes (lecture and tutorial) Program listings, assignments, old exam papers and

revision

Uses include Exam this is the ONLY material that you may take into

the examination

Resources

Unit MyLO Web site lecture recordings tutorial and activity work assessment information

Python Web sites http://docs.python.org/2/tutorial/ http://wiki.python.org/moni/BeginnersGuide/

Programmers http://www.learnpython.org