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IST Yearly Notes
Data bases
Components of a Database
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File - A file is a block of related data stored on a storage device (such as an employee
database). A file in a database is divided into a set of related records.
Record - A record is a collection of facts about one specific entry in a database. All the
information about one employee is a record. A record is divided into one or more
related fields.
Field - A field is a specific piece of data in a record. Fields for each employee include
the employee ID, last name and first name. A field is also known as a data item or
category and is made up of characters.
Character - A character is the smallest unit of data that people can handle and
includes letters, numbers and special symbols.
Data Dictionaries
A data dictionary is a comprehensive description of each field in a database. It contains
information about the characteristics of each item entered in the database, such as the field
names, data types, field sizes and field descriptions – see below –
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Field name is the name of the field; they should be short, clear and avoid the use of
punctuation.
Field size or field width, is the number of characters allowed in each field.
Description specifies the contents of the field.
© iRuler 2008
Data Types
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Data type or field type is the kind of data in the field. Each field stores data of a single
data type. Some common data types include:
o Text - used for text or numbers that do not require calculations
o Memo - used for lengthy text and numbers such as descriptions
o Number - used for numeric data to be included in mathematical calculations
o Currency - used for currency values
o AutoNumber - Used to create a number automatically when record is added
o Yes/No – Used for data that can only be of two values, cannot be empty or null
o OLE object - used for data created in other programs such as a spreadsheet,
graphic or sound
o Hyperlink - used for hyperlinks
o Date/Time - used for dates and times.
The organisation of data often involves a key (field to sort and retrieve information).
A primary key is a field in which each item is unique and must have a value.
AutoNumber is a good choice for primary key.
Purpose of:- Form
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A form or label displays data for every field of a single record and the layout
can be changed. The user can position fields, headings, instructions and
graphics. A well-designed form provides information explaining the required
data and any data entry rules that apply to particular fields. For example, a
field name ‘Sex (M/F)’ leaves no confusion about its required data. Size, stroke
weight and colour of the font impact on the user and the accuracy of the data
entered. After one record has been completed the next record appears until all
data is entered.
- Table
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A table or list displays data using columns (fields) and rows (records). You can
scroll up & down to view more columns and rows. Good for Several Records or
entering new data in only one field. Screen Layout can be changed by
adjusting width, height and hiding columns. Data in a table is usually entered
using a form, retrieved using a query and printed using a report.
- Query
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A query is a search of a database for records that meet a certain condition. It is
a question you ask of the database. The results of a query are displayed in a
table but can be used as the basis for a form, report, graph or another query.
- Report
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The purpose of the report will determine its content, format and style. Before
creating a report the user may need to select the required records by
constructing a query.
Difference between Searching and Sorting
- Searching
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Searching is the process of locating data and information. For small databases
the ‘Find’ or ‘Search’ commands are adequate but for large databases you
should construct a query.
- Sorting
o Sorting is the process of arranging data in a particular order (organising data).
Sorts can be performed in either ascending or descending order
© iRuler 2008
Methods of Editing Data
Editing is changing data. (Inserting, Deleting, Changing or Modifying Data structure)
- Inserting Data. New records can be inserted by the correct command. Records can be
rearranged by sorting.
- Deleting Data. To delete a record, the user selects the records and then presses the
Delete key or chooses an appropriate command.
- Data is moved and copied using the Cut, Copy and Paste commands.
- The structure of the database can be edited to meet new requirements. This involves
changing the data dictionary.
Internet
Difference between Internet and Intranet
- Internet –
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The Internet is a connected set of networks using the TCP/IP standard with
millions of computers linked all around the world. Provides intstant access to
information (news, weather, sports, share prices and educational materials).
Also provides services - Sending messages, banking, shopping, playing games
and listening to music. Access to the internet is available from almost anywhere
around the world through an ISP.
- Intranet
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An intranet is a private network that uses a similar interface to the Internet
existing within an organization. Intranet supports email, newsgroups, file
transfer, web publishing with access through a web browser.
Parts of a URL
A URL (Uniform Resource Locator) is the address of a file or resource on the Web in a lower
case, single unbroken line without spaces.
http://www.hi.com.au/heinneman/default.htm
There are three parts to a URL:
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Protocol—indicates access to a particular resource on the Web. For most cases the
protocol will be http://. It allows access to web pages based on hypertext.
Domain name—address of the specific computer where the resource is located such
as www.hi.com.au. The domain name is interchangeable with the IP address.
File path—full path to the file to be retrieved. It may be a simple file name or a
directory path, such as /heinneman/default.htm. The domain name and the file path
are separated by a forward slash (/). The file being retrieved in this example is
default.htm.
Main Parts of an Email Header
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To—main person receiving the message
Cc—carbon copy sends the same message to other people just as information for
them
Bcc—blind carbon copy sends a copy to other people without revealing who else got
the message
Subject—is the topic of the message or brief description—this is very useful for the
receiver of the message, also displayed outside for the person to click on.
© iRuler 2008
Email attachments
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An attachment is a file in its original condition and format that is sent with the email
message. When sending an attachment it is important to include a brief explanation in
the main body of the email message. The file name and the format of the attachment
should be easily understood.
Netiquette
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Netiquette is a code of acceptable behaviour users should follow on the Internet. It
covers rules for all aspects of the Internet such as the email, chatting, newsgroups and
discussion groups. Some of the rules for netiquette include:
o keep messages short and to the point
o be polite and avoid offensive language
o avoid sending abusive or insulting messages (flames)—do not participate in
flame wars
o avoid using all capital letters as it is considered shouting
o use emoticons to express feelings such as :) for happy or :( for sad
o use abbreviations and acronyms such as ‘IRL’ for ‘in real life’ or ‘BTW’ for ‘by
the way’
o Make the email subject line as meaningful as possible.
Search Engines and how they work
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A search engine is a program that finds websites and web pages. It accesses a
database of indexed websites that can be searched using a keyword. This index is
built by regularly scanning for new websites and accepting submissions from website
authors.
A web directory organises the Web into categories and then smaller subcategories.
This allows the user to browse through the categories until they find a relevant site.
Most search engines allow users to search for specific items such as images.
Some search engines allow a search to be restricted to just Australia
Advance search options provide users with more accurate results. (Such as restricted
to files that were updated recently, particular file formats or sites without certain
words)
Internet Protocols
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A protocol is a set of rules that governs the transmission of data between computer
devices; protocols include TCP/IP, HTTP, FTP and SMTP.
Transmission Control Protocol/Internet Protocol (TCP/IP) is a common language for
data transmission and error detection across the Internet. It works by breaking
information into smaller packets of data. Each data packet contains the information
and the address of the receiving computer. The TCP tells what is in the packet and IP
tells the receiving computer where and how to send the packet.
Hypertext transfer protocol (HTTP) is a standard for transferring the contents of a web
page into a browser for viewing. Does not download files that make up the web page.
HTTP is a one-way system as data is only transferred from the web server to the
browser.
File transfer protocol (FTP) is a standard to upload and download files. An FTP server
is a computer that allows users to upload and download files using FTP. FTP is a file
server not a web server.
Simple mail transfer protocol (SMTP) is a standard for outgoing email. Most email
messages are sent using SMTP. POP3 (Post Office Protocol) is a standard for incoming
email.
© iRuler 2008
Cookie
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A cookie is a file that is stored on the hard disk after the user visits a website. It is used
to measure a user’s behaviour and work flow habits. Cookies store the information
about the web pages visited and the transactions completed. However, most cookies
are designed to improve your experience and allow organisations to target
advertisements to your tastes. Users have the option to block or accept cookies.
Proxy Server
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A proxy server is a barrier to the Internet to ensure users are securely and
productively accessing network resources. It lets administrators limit access to
objectionable content by filtering URLs. Proxy servers distribute and manage
information reducing network traffic and user wait times. Traffic time is reduced as
the proxy server caches frequently accessed documents or entire websites.
Firewalls
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Firewalls are used on the Internet or any network to check all incoming data for the
purpose of verification and authentication. It aims to protect a computer system from
hackers trying to access sensitive information. Firewalls are an important security
measure on an intranet. All messages entering or leaving the intranet pass through
the firewall. It examines each message and blocks those that do not meet the
specified security criteria.
Antivirus Software
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Anti-virus software is used to scan a file or disk for a range of known viruses. A virus is
a small program that attaches itself to an application. There is no guarantee that antivirus software will stop every virus, as new viruses are constantly appearing.
However, if users download the latest virus definition files and regularly use the antivirus program, it will minimise the problem
Website Development
- Types of Web Pages and Purpose
o Home Page
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Home page (index page) is the first page viewed by a visitor and
provides information about the purpose and subject matter of the
website; it provides a link to other web pages.
o Intermediate Page
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An intermediate page is the next level down from the home page. It
provides link back to home page. They provide structure and assist in
the navigation of the website. Way of grouping Content pages.
o Content Page
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Content pages contain topic details and are usually accessible from
intermediate pages. Content pages usually contain a link to home page.
Features of a Website
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Contact information—Information such as address, phone, fax and email.
Text—Look and style is important. Should display the essential content.
Graphic—Add interest and attraction. Most common formats are JPEG and GIF.
Thumbnail image—small preview of the ‘real’ full size image. Downloads faster than
the full size image. Viewer can click the thumbnail to view full size image.
- Rollover—picture, icon or button that changes when the mouse is moved over it. A
rollover is 2 images. GIF is mostly used as it needs to be changed quickly.
- Animation—a flashing object to get visitor’s attention. Animation is used to direct the
visitor to an area of the screen or an interesting feature.
© iRuler 2008
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Streamed audio—used to provide background music or sound effects. Streaming
audio is heard before the entire file has been transferred.
Streamed video—video clips that play before the entire file has been transferred. It is
more dependent than streamed audio on a high bandwidth.
Hyperlink—link to another part of the same web page or web site. Hyperlinks are
made using text (hot word) or image (hot spot). Hyperlinks are usually underlined or
coloured. Often arranged in horizontal rows or vertical columns to form a navigation
toolbar.
Tables—rows and columns of cells that are filled with characters or graphics. Used to
arrange information in row and column format, borders and shading can be applied.
Lists—unordered lists do not have a numbered sequence. Entry in an unordered list is
usually shown with a bullet. Ordered lists use a numbered sequence.
Frames—space or boxes that hold an object. Each frame is considered a separate
window and could be a separate HTML document. Frames allow a banner, advertising
message or animation to be held in place while the visitor navigates the website.
Web forms—are tools to collect information, such as orders for goods and services
and results from surveys. Web forms have an invisible part that processes the data
and stores it in a database. Information is entered using text boxes, option buttons,
check boxes, list boxes, spin boxes.
Design Considerations for a website
o Consistency—layout, format and style should be the same throughout the
website unless different data types demand a change. Readability is improved
when similar items are grouped.
o Navigation—Colouring different areas of the page, using visual symbols (icons
and arrows), inserting clear page headers and creating simple hyperlinks
improves navigation.
o Simplicity—do not overuse design elements as this will create visual clutter
and confuse the visitor. The overuse of colour, sound and animations can be
distracting. First impressions on the Web are important. A visitor often forms
an opinion of a website within the first minute of accessing the home page.
- Design Factors
o Text—clear and legible text using at most three different fonts. Care should be
taken using font styles such as bold and italic. Underlining is only used for
hyperlinks. Long lines of text are difficult to read.
o Colour—many different colours can be distracting and reduce readability. A
colour scheme should not interfere with the main message of the web page.
Dark text on a light background or vice versa usually works well. Blue is often
preferred for unused links and purple for used links.
o Graphics—are used to create interest, however, they are slow to download.
When using graphics consider the size of the graphic, recognisable icons and
whether the graphic fits easily on the screen.
o Animation—visitors seeking information from a website are distracted by
inappropriate animation. A small creative animation such as a comet-type
effect can be effective.
o Audio and video—should not be an essential part of a web page as some
visitors might not have the right hardware or plug-in. It is good practice to
advise visitors about the size of audio and video files.
© iRuler 2008
Networking
Advantages and Disadvantages of setting up a network
- Advantages
o Sharing peripheral devices: Share Printers, Hard disks and Internet access.
o Sharing applications: Networks enable users to share applications. Usually a
network licence is cheaper and can be installed faster.
o Sharing data: Networks provide a very fast method for sharing and transferring
files. Many networks have a file server to store data which can be accessed
from any computer on the network. This increases productivity and efficiency.
o Security of information: Networks secure files by restricting access to only
authorised users. The entire network is backed up on a regular basis. Firewalls
are used to protect data on the network from hackers and unauthorised users.
o Improved communication: Networks enable users to work together in ways that
otherwise would not be possible with Email and messaging systems. There is
also a range of software designed for groups of users on a network. One
example of this software is project management software. It is a tool to
efficiently plan, manage and communicate information about a large project.
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Disadvantages
o Expensive to install: Servers, network devices, cables and network software are
expensive. Technician will be required to setup a network but saves money
over time.
o Administrative time: Maintenance requires time and a person called a Network
Admin to be employed for looking after the network.
o Server failure: If the server fails no one can access the network and its devices
and productivity can be lost.
o Damaged equipment: One network cable can stop the entire network from
functioning. A faulty network Interface card will stop a user from accessing the
network.
o Maintaining security: Networks are targets for hackers and viruses. The files
stored on a network can be accessed, stolen and edited more easily than files
stored on an individual computer. A virus that enters the network can spread to
every computer on the network. Appropriate procedures need to be
implemented to maintain security such as corporate anti-virus software and
powerful firewalls.
Protocols used over Networks
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TCP/IP (Transmission Control Protocol/Internet Protocol) is a standard for data
transmission and error detection across the Internet. The TCP standards inform the
receiving computer what is inside the data packet and the IP standard tells the
computer where and how to send the data packet.
- IPX/SPX (Internetwork Packet Exchange/ Sequenced Packet Exchange) is a standard
used for data transmission in local area networks (LAN) that use the Novell NetWare
operating system.
- NetBEUI (NetBios Extended User Interface) is a standard used for data transmission in
local area networks that use Windows NT and LAN manager.
- AppleTalk is a set of local area network standards for Apple Macintosh computers. It is
built into all Apple computers and Apple laser printers.
© iRuler 2008
Types of Wire Transmissions
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Twisted-pair cable consists of pairs of insulated copper wires, twisted to form a spiral.
Twisting reduces the amount of interference from other cabling. Unshielded twistedpair (UTP) is used on a network. There are two common standards for UTP called
10Base-T (10 Mbps Ethernet) and 100Base-T (100 Mbps Fast Ethernet). UTP is
preferred as it is cheap and easy to install with a maximum distance of 100m.
Coaxial cable has a single copper wire surrounded by an insulator, grounded
shielding and an outer insulator. The shielding allows data to be transmitted with little
distortion. It is more dependable than UTP, however, it is more expensive and less
flexible. The most common standard for coaxial cabling is 10Base2 (10 Mbps
Ethernet). It is suitable for a maximum distance of 200 metres.
Optical fibre cable is a very thin fibre of clear glass or plastic that carries light waves.
Optical fibre cable is becoming the standard for wire transmission. Optical fibre
cables are free from electromagnetic and radio interference, very secure, light and
transmit data at high speeds without errors. Optical fibre cables can, in theory,
transmit data in excess of 10 Tbps. However, they are more expensive than other
types of wire transmission. Optical fibre is suitable for long distances.
Transmission Modes
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Simplex mode allows transmission in one direction only, from the sender to the
receiver such as - radio, television or a school broadcast system. Remote sensors
send information to a computer using simplex mode.
Half duplex mode allows transmission in both directions but not at the same time. This
means the sender and the receiver take turns. An example of half duplex mode is an
intercom or walkie-talkie. Disk drives and printers transfer information using half
duplex mode.
Full duplex mode allows transmission in both directions at the same time. Most
communications systems use full duplex mode, such as the telephone or email. A
computer uses full duplex for most of its communication.
Bits per second
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Bits per second (bps)—number of bits transmitted in one second also called bit rate.
Baud Rate
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Baud rate—the maximum number of electrical signals transmitted in one second.
Baud Rate can transmit more then one Bit a second, for example 1 baud rate = 2 bps.
Wireless Transmission
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Radio waves are used to transfer data by connecting a small radio transmitter to each
device which transmits across the air. Most common wireless networking standards
are 802.11b (11 Mbps) and 802.11g (54 Mbps). Radio Waves have bad security and
can be intercepted by anyone.
Microwave is a high frequency radio signal sent through space in a straight line from
one antenna to another and can send both voice and data. Antennae are placed on
high grounds to transmit over long distances. Microwaves are mostly error free but
weather conditions, trees or building will obstruct the signal. Microwaves are
commonly used with satellites for long distances.
© iRuler 2008
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Satellites are specialised receivers and transmitters that are launched by rocket and
placed in orbit around the earth. A signal is sent from one ground station to the
satellite, which receives and re-transmits the signal to another ground station. Each
ground station uses a satellite dish to send and receive the signals. Satellites can
transmit large amounts of data over long distances and at great speeds. There are
hundreds of satellites currently in operation. They are used for weather forecasting,
television broadcasts, radio communications and Internet communications.
Difference between LAN, WAN and VPN
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A local area network (LAN) is a network on one site, such as within a building or group
of buildings. A LAN is often a collection of computers and peripheral devices. LANs
enable users to share resources and communicate with each other more effectively.
These tasks are completed using a network operating system (NOS). The physical
arrangement of the devices on a LAN is called the network topology. There are many
possible network topologies, such as star, bus and ring.
A wide area network (WAN) is a network that covers a very large area. It is often made
up of a collection of LANs. A WAN may use a private leased line, the normal
telephone network or a combination of both. A private leased line is dedicated to the
network. It offers higher transmission speeds and more accurate transfer of data than
those available through the Public Switched Telephone Network (PSTN). PSTN links
are relatively cheap if computers do not require constant connection. However, the
link is not guaranteed and can be interrupted.
A virtual private network (VPN) is a private network carrying encrypted data across
the Internet. It uses the PSTN and the Internet to create an organisation’s network. A
VPN aims to provide an organisation with the same capabilities as a LAN but at a
much lower cost. It uses encryption and other security measures to ensure only
authorised users have access to the VPN. Encryption is the process of coding data and
decryption the process of changing it back. Data is coded, transmitted and then
converted back to its original form. Encryption is used to prevent data from being
intercepted during transmission and to maintain the privacy of the VPN.
Types of Servers
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A file server is a controlling computer in a network that stores the programs and data
shared by users. The files stored on this server can be retrieved by authorised users.
A print server is a computer in a network that controls one or more printers. Print
servers have printers attached to them and are accessed by authorised users. If the
printer is busy the data to be printed is stored in the print server and placed at the
end of a queue. A print server can be used with or without a file server.
A mail server is a computer in a network that provides email facilities. It stores
incoming mail for distribution to users and forwards outgoing mail to appropriate
devices. Some mail servers can be accessed from the Internet.
A web server is a computer in a network that stores and distributes web pages. When
a network user accesses a web page from the Internet it is stored in the web server.
Websites are downloaded and stored on web servers. When you browse the Internet
you are travelling from one web server to another.
Network connection devices
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A workstation is a personal computer on a network. It has memory, storage and
processing capabilities. Workstations can operate independently of the network.
They access a server for files and applications but process the data themselves.
- A hub is a central connecting device in a network. Each node is connected directly to
the hub. Most hubs were initially dumb. They receive a data packet from one node
© iRuler 2008
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and send that data packet to all nodes on the network. This created a lot of
unnecessary network traffic, as most of the nodes will ignore the data because it is not
addressed to them. A better type of hub is called a switch.
A switch is an intelligent hub that only sends data to a specific node. The switch looks
at the address of the data packet and sends it to that address. A switch reduces the
volume of traffic on a network compared to a hub.
A router is a very intelligent hub that directs (routes) data packets to and from other
networks. It makes its decision on its current understanding of the networks. A router
maintains a table of the available routes and their conditions. It uses this table to
determine the best route for a given data packet. Routers are often used to connect to
the Internet.
A bridge is a device to link two similar networks. It often connects networks that use
the same protocol such as Ethernet. A bridge examines each data packet on a
network and forwards any data packets addressed to a connected network.
A gateway is a link between two different types of networks. It converts different
protocols and transfers data between the two networks. For example, a gateway
could be used to convert a TCP/IP packet to an IPX packet. A gateway acts as the door
between the networks. All the data must pass through the gateway to reach the other
network. Gateways are not necessarily separate devices but rather are often pieces of
software running on servers or in routers.
A repeater is used to rebuild a fading signal to its original strength and shape before
transmitting it onwards. For example, the data sent along a UTP cable becomes
unreadable after about 100 metres. A repeater would be installed every 100 metres to
rebuild the signal. A repeater ensures that the data is received as it was sent.
A network interface card (NIC, pronounced ‘nick’) is an expansion card that allows a
device to be connected to a network. NICs are installed into servers, workstations
and some other devices. Each device must have a driver to communicate on the
network. A NIC is usually given a unique address so that it can be identified on the
network. Most NICs require a network cable connection and have connectors on the
card for different types of cables.
Client Server
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A client–server network is a network that uses one or more computers as servers and
all the remaining computers as clients. Each server is a powerful computer that
contains resources to be shared with clients. Most organisations use the client–server
network for their LAN. A client–server network involves using a network operating
system (NOS). A NOS allows the server to complete requests from clients for
resources. The majority of the NOS is installed on the server but each client has NOS
client software. The NOS client software is used to send requests to the server.
Peer-to-Peer Network Server
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A peer-to-peer network is a network where there is no central server but each
computer is both a server and a client. It is a simple network that usually connects
less than ten computers. A peer-to-peer network is used in homes and small offices to
share files, peripheral devices and one Internet connection. In a peer-to-peer
network each computer is considered a peer because it is equal and shares resources
with others without a server. Each user determines which resources on their
computer are to be shared. Operating systems such as Windows XP and Mac OS have
the software to operate a peer-to-peer network. A P2P is an Internet peer-to-peer
network on which users connect directly to each other’s hard disks and exchange
files over the Internet.
© iRuler 2008
Network Topologies
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Network topology is the physical arrangement of the devices on a LAN. The type of
network topology is not determined by the shape but by how each node is connected
to other nodes. There are many possible network topologies:
o A star topology has a central node with each device connected directly to it.
The central node is usually a hub, switch or router. The central node receives
messages and sends them to the destination device. Star topology requires
extra cabling as each device needs a cable to the central node, not the nearest
device. If one device or cable is broken the network can still operate.
However, if the central node fails then the network fails.
o A bus topology is an arrangement where all the nodes are attached to a cable
called the bus. Each device has a unique identity and can only recognise those
signals intended for it. Nodes check the bus, and retrieve their messages as
data travels along the bus. Each node is considered to be connected to every
other node and can communicate directly along the network to any device. Bus
topology is one of the easiest and cheapest to set up. It can still operate if one
node fails and nodes are easily added. However, a faulty bus will stop the
network and data collisions can occur on the bus.
o A ring topology is an arrangement where all nodes are attached in the shape of
a closed loop. Each device in the ring has a unique address. Data flow is in one
direction, moving from node to node until it arrives at its destination. Ring
topology is dependent on the ring—if it is faulty the network will stop.
Network Operating Systems and tasks
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Network operating systems control the flow of data between the devices on the
network and the requests for data. The network operating system organises messages
from nodes until the network is ready to process the message. The tasks performed
by a network operating system and the administrator of the network include:
o Administration—adds, removes and organises users. Groups of users are often
given the same permissions and rights. Permissions and rights allow access to
particular files and resources.
o File management—gives users access to the remote hard disks on the server. It
provides a file system and the ability to manage a network directory. Drives
and directories are mapped for users.
o Applications—handles requests from users to share applications. The NOS is
used to install software. It is easier for network administrators to comply with
software copyright laws using a network. Access to the application files is
restricted.
o Resource management—allows network devices such as printers and modems
to be shared. It assigns users to printers and orders print jobs. The NOS is able
to track the use of resources. This assists with budgeting.
© iRuler 2008
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Security—monitors and restricts access to network resources. It is often much
easier to secure data on a network compared to securing data on a large
number of computers. Anti-virus software is used to protect the network from
viruses. Regular backups are implemented for data stored on the network.
Programming
Six Basic Programming Concepts
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Function (or keyword) - is a reserved word for a particular purpose such as class,
public and private. Some functions are very powerful, such as if and while.
Constant (or literal) - is an item of data with only one specific value. Constants are
either numbers or strings (numbers and letters).
Variable - is an item of data that may take different values, one at a time. They are
storage containers used to hold data of the same type.
Identifier - is the name of anything in a program such as a variable. There are some
restrictions on the use of identifiers, such as always starting with a letter.
Separator - is a symbol for grouping sections of the program such as { and }. The
correct use of separators is essential otherwise the program will not work.
Assignment statement - gives a value to a variable such as: x = 9. The general form of
an assignment statement is: variable = expression. The expression can contain other
variables such as: y + 1. This will result in the assignment statement: x = y + 1.
Data Types
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Data type is the kind of data that can be stored in a variable. To create a variable it
must be declared. Variable declaration involves stating the data type of the variable
and an identifier or unique name for the variable. Most programming languages have
the following data types:
o Integer number is a whole number without fractional parts
o Floating-point number is a number with the fractional parts
o Boolean is used to store values that have one of two possible states such as true
or false
o Character is used to store one character such as a letter, number or symbol
o String is used to store more than one character.
Data Operators (used to represent an action such as calculation)
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Arithmetic operator—performs a calculation such as addition (+), subtraction (–),
division (/), multiplication (*), powers (^) and modulus (%). Calculations are carried
out using the standard order of operations.
Relational operator—compares two values and returns a boolean (true or false) result.
Relational operators include less than (<), greater than (>), less-than-or-equal-to
(<=), greaterthan- or-equal-to (>=), equal-to (= =) and not-equal-to (!=).
Logical operator—compares two values and returns a Boolean (true or false) result.
Logical operators include AND (&&), OR (!!) and NOT (!).
Algorithms, Pseudocode and flow charts
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An algorithm is a series of steps designed to solve a problem in a finite time. An
algorithm can be used to solve many types of problems. Algorithms are not programs
but are an important part in the development of a program.
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Algorithm to make a phone call:
Pick up the phone.
Dial number.
Deliver the message.
Hang up the phone.
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Pseudocode uses indented lines and keywords to describe an algorithm. Pseudocode
is written using a word processor and is similar to many programming languages.
There are different standards of pseudocode for different purposes; however, there
are some generally accepted rules. The flow of control in pseudocode is always from
the top to the bottom. The keywords are highlighted in capital letters (or bold) to
emphasise them and to indicate the type of action being performed. These keywords
are grouped together in pairs. For example, for every BEGIN there is an END, for
every IF there is an ENDIF. Indentation is used to show the structure of the algorithm.
A flowchart is a pictorial or graphical method of describing an algorithm. Flowcharts
often make it easy to see the structure of the solution. However, it is very easy to draw
a flowchart that is complex and difficult to change into a programming language. The
basic elements of a flowchart are a set of symbols that contain messages and
interconnecting lines. A set of standards for flowcharts has been established for a
number of different applications. Most common Symbols Shown Below
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Low-level Programming Languages
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Low-level languages are the lowest level of computer languages and depend on the
hardware of the computer. Programs written using low-level languages are often
called machine code or assembly code. They process calculations much faster than
high-level languages.
High Level Programming Languages
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High-level languages use English-like codes where each statement corresponds to
several lines of machine code. Programming languages such as Java, Visual BASIC
and C++ are high-level languages. A compiler or interpreter translates a high-level
program into machine code so the computer can implement the solution.
Sub Programs
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A subprogram is a self-contained section of code that performs a particular task. In
Java, subprograms are called ‘methods’. For example, the code below is a method in
Java. It adds two integers (parameters) and returns the result to the calling program
(larger program).
Public int add2Int (int x, int y)
{
Int result;
result = x + y
Return result;
}
Subprograms have a single entry point and suspend the calling program until they
have finished. Subprograms have the added advantage of being reusable.
Programmers may use the same subprogram many times in different problems. This
reduces the time required to program. Programmers keep a ‘library’ of subprograms
they have written.
Data Structures
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A file is a block of related data stored on a storage device. Programs are stored as
files. A data structure used in many programming languages is called a record. A
record is a collection of facts that are related in some way. Records are a fixed length
and are divided into one or more fields. A field is a specific piece of data in a record.
Shown below is a record that consists of 17 characters: eight for field 1, seven for field
2 and two for field 3. Each record, irrespective of the data, would have a fixed length
of seventeen characters. A record is usually a combination of other data types. The
record below has a string data type and an integer data type. The ability to have
different data types distinguishes records and arrays.
An array stores a list of elements of the same data type. An array is used to efficiently
store large quantities of data. Each element within an array is numbered and
accessed based on their number. To use an array the data type and the number of
items must be declared. For example, array declarations in Java are shown below.
Int[] score = new int[10];
char[] vowel char[5];
The first statement creates an integer array ‘score’ with up to ten elements. The
second statement creates a character array ‘vowel’ with up to five elements. After the
array is declared each individual element can be used to store data. In the example
below vowel[1] is storing the letter ‘E’.
vowel[0] = ‘A’;
vowel[1] = ‘E’;
vowel[4] = ‘U’;
Program Errors and ways of Detection and Correction
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Logic errors result from an incorrect series of steps to solve the problem. The
program with a logic error produces incorrect or unexpected results. Logic errors
can occur if the algorithm does not solve the problem correctly. The algorithm should
be tested before coding to eliminate logic errors. It is often a difficult task to find and
correct logic errors.
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Syntax errors are made when the programmer has failed to follow the rules (syntax)
of the programming language. A syntax error may be a spelling error or a symbol
that cannot be translated. When the program is compiled or interpreted, an error
message will appear if the program contains any syntax errors. Correcting any syntax
errors is usually a simple task.
Run-time errors occur when it is impossible for the computer to carry out the
instruction. For example, if a calculation attempted to divide a number by zero it
would be a run-time error. The instruction has the correct syntax but it is not possible
to carry out the instruction. Incorrect data can often produce a run-time error. There
is a range of strategies to detect and correct errors:
Desk checking involves the programmer checking each line of code. Desk checking
takes place after the algorithm has been written and again after it has been coded in
the programming language. The programmer executes the program the same as the
computer. Desk checking provides a way to see exactly what code is being executed
and the flow of execution through the program. A desk check usually involves
watching the variables. A list is constructed containing the names of variables and
their values. The list of variables is updated after each step of the desk check. If the
desk check is performed by somebody other than the programmer it is called a peer
check.
Breakpoint is a roadblock in the execution of the program. When the program
reaches a breakpoint it stops. Breakpoints are useful in isolating sections of the code
and analysing them.
Software debugging tools are available for most programming languages. A
debugger is a program that will perform the desk check electronically. They are often
used with a breakpoint to watch the variables in a section of code. Debuggers are
only tools to find problems and do not provide the solution to the problem.
Control Structures
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Programmers solve a problem by designing an algorithm and then coding the
algorithm into a programming language. Algorithms and programming languages
consist of control structures. Control structures are the building blocks of the program.
There are three basic control structures: sequence, selection and repetition.
Sequence
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Sequence is the order the steps are executed. In pseudocode, the steps are placed
between BEGIN and END (see the problem below). The sequence of
four steps is indented to show structure and to improve the
readability of the algorithm. The flow of control is top to bottom,
starting at the first step and finishing at the last step. Flowcharts
always start and finish with a terminal symbol (oval). The steps are
placed between these symbols and joined by flowlines. The
direction of flow is down the page between the terminal symbols.
Problem: Design an algorithm to wash your hands.
Pseudocode solution
BEGIN
Wet hands
Clean hands with soap
Rinse off soap
Dry hands
END
© iRuler 2008
Flowchart for this shown 
Selection
Selection is used to make a logical decision. It requires a choice to be made between two or
more options. The choice is made depending on the answer to a condition. There are two
types of selection: binary and case.
- Binary selection involves two choices. In pseudocode, the keywords IF … THEN …
ELSE are used for binary selection (see the problem below). The condition is put after
the IF keyword. There are only two possible answers to the condition, true or false. If
the condition is true then the process after the THEN keyword is executed. If the
condition is false then the process after the ELSE keyword is executed. The ELSE
statement is not always required and can be omitted. In a flowchart the selection is
made using a decision symbol (diamond). The condition is placed inside this symbol
and the answer must be true or false. It is very important that the two flowlines from
the decision symbol are labelled with true or false to determine which path to follow.
The two flowlines join together to complete the binary selection.
Problem: Design an algorithm for turning on the lights.
Pseudocode solution
BEGIN
IF night
THEN turn lights on
ELSE turn lights off
ENDIF
END
Flowchart solution shown 
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Case selection (or multiway selection) involves more than two choices. In
pseudocode, the keywords CASEWHERE … ENDCASE are used for case selection
(see the problem below). The condition is put after the CASEWHERE keyword.
Careful thought is required to cater for all possible answers to the condition. The
possibilities are indented under the CASEWHERE keyword with a process to be
executed only if the answer is true. In the problem below there are three options:
green, amber and red with a colon specifying the process to be carried out if the
option is true. In a flowchart the case selection is made using a decision symbol (see
below). The condition is placed inside the decision symbol with the answers above
each process. The flow lines join together to complete the case selection.
Problem: Design an algorithm for a set of traffic lights.
Pseudocode solution
BEGIN
signal
CASEWHERE
colour
of
Green : Pass through
lights
Amber : Slow down
vehicle
END
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Red : Stop vehicle
ENDCASE
Flow Chart Solution Shown 
Repetition
A repetition or loop allows a number of steps to be repeated until some condition is satisfied.
The steps to be repeated are referred to as the body of the loop. It is very important that
each loop contains a condition to stop the loop going on forever. There are two types of
repetition: pre-test or post-test. In a pre-test repetition or guarded loop the condition is
checked at the beginning of the loop before the steps to be repeated are executed. In
pseudocode the keywords used for a pre-test repetition are WHILE … ENDWHILE (see
problem below). The condition is put after the WHILE keyword and the body of the loop
between the WHILE and ENDWHILE keywords. In a flowchart the pre-test repetition is made
using a decision symbol and flow lines. The condition is placed inside the decision symbol
and checked before the body of the loop.
Problem: Design an algorithm for using seat belts in a car.
Pseudocode solution
BEGIN
END
WHILE car is moving
keep seat belts on
ENDWHILE
Flowchart solution shown below –
In a post-test repetition or unguarded loop the condition is checked at the end of the loop
after the steps to be repeated are executed. In pseudocode the keywords used for a posttest repetition are REPEAT … UNTIL (see problem below). The body of the loop is
underneath the REPEAT keyword and the condition is after the UNTIL keyword. In a
flowchart the post-test repetition is made with a decision symbol and flowlines. The body of
the loop is executed before the condition is met in the
decision
symbol.
Problem: Design an algorithm to cut the grass.
Pseudocode solution
BEGIN
© iRuler 2008
REPEAT
Use lawn mower
UNTIL grass is cut
END
Flowchart Solution shown 
© iRuler 2008