COURSE CONTENTS

CMP 101: INTRODUCTION TO COMPUTER SCIENCE: (3 Units) (L 30: P: 45)

History of Computer Science and their generations. Computer Hardware; functional
components Modern I/O units Software: Operating Systems, Application Packages, Program
Development; Flow charts and algorithms; Program Objects, Introduction to FORTRAN,
BASIC or VISUAL BASIC Fundamentals.

OBJECTIVES
The specific objectives of this course are to:
1. Understand the history, classification and impact of computers.
2. Know the concept of computer hardware and software.
3. Understand features of a good program.
4. Understand the concept of Algorithms and flowcharting.
5. Understand the principles of designing algorithms for common programming problem.
6. Understand the concept of debugging and maintaining program.

LEARNING OUTCOMES
The students should be able to:
1. Define computer
2. Know the history, classification and computer applications
3. Know the concept of computer hardware
4. Know the concept of computer software.
5. Know the data preparation methods
6. Know the Characteristics of a Computer.
7. Know features of a good program.
8. Explain the concept of Computer problem solving techniques, Algorithms and
flowcharting.
9. Explain General modular program design principles.
10. Explain expressions and control structure.
11. Explain the procedure in solving programming problems.
12. Explain the concept of debugging and maintaining program.
13. Know programming style in BASIC
14. Know how to debug programs in BASIC.

TEXT BOOK(S):
1. Goel, A. (2010). Computer fundamentals. Pearson Education India.
2. Chivers, I. D., & Sleightholme, J. (2018). Introduction to programming with Fortran
(Vol. 2). Cham: Springer.
Course Writer/Developer: Dr. F.E. AYO, Department of Mathematical Sciences, Computer
science unit, Olabisi Onabanjo University, Ago-Iwoye.
E-mail: ayo.femi@oouagoiwoye.edu.ng
LESSON 1
DEFINITION OF COMPUTER
A computer is an electronic device that accepts data from the user, processes it, produces
results, displays them to the users, and stores the results for future usage.
In other words, a computer is basically defined as a tool or machine used for processing data
to give required information. It is capable of:
1. taking input data through the keyboard (input unit)
2. storing the input data in a diskette, hard disk or other medium
3. processing it at the central processing unit (CPU) and
4. giving out the result (output) on the screen or the Visual Display Unit (VDU).

Figure 1: Schematic diagram to define a computer

Data is a collection of unorganized facts & figures and does not provide any further
information regarding patterns, context, etc. Hence data means "unstructured facts and figures".
Information is a structured data i.e. organized meaningful and processed data. To process the
data and convert into information, a computer is used.
Methods of Data Processing
The following are the three major methods that have been widely used for data processing over
the years:
a. Manual method
b. Mechanical method and
c. Computer method.
Manual Method
The manual method of data processing involves the use of chalk, wall, pen, pencil etc. These
devices or tools facilitate human efforts in recording, classifying, manipulating, sorting and
presenting data or information. The manual data processing operations entail considerable
manual efforts. Thus, manual method is cumbersome, tiresome, boring, frustrating and time
consuming. Furthermore, the processing of data by the manual method is likely to be affected
by human errors. The manual method does not allow for the processing of large volume of data
on a regular and timely basis.
Mechanical Method
The mechanical method of data processing involves the use of machines such as typewriter,
adding machines and the like. These machines facilitate human efforts in recording, classifying,
manipulating, sorting and presenting data or information. The mechanical operations are noisy,
hazardous, error prone and untidy. The mechanical method does not allow for the processing
of large volume of data continuously and timely.
Computer Method
The computer method of carrying out data processing has the following major features:
a. Data can be steadily and continuously processed.
b. The operations are practically not noisy.
c. There is a store where data and instructions can be stored temporarily and permanently.
d. Errors can be easily and neatly corrected.
e. Output reports are usually very neat, decent and can be produced in various forms such as
adding graphs, diagrams, pictures etc.
f. Accuracy and reliability are highly enhanced.

CHARACTERISTICS OF A COMPUTER
The characteristics of the computer system are as follows –

Figure 2: Characteristics of computer

Speed
 Computer is a very fast device.
 It is capable of performing calculation of very large amount of data.
 The computer has units of speed in microsecond, nanosecond, and even the picosecond.
 It can perform millions of calculations in a few seconds as compared to man who will
spend many months to perform the same task.
Accuracy
 In addition to being very fast, computers are very accurate.
 The calculations are 100% error free.
 Computers perform all jobs with 100% accuracy provided that the input is correct.
Storage Capability
 Memory is a very important characteristic of computers.
 A computer has much more storage capacity than human beings.
 It can store large amount of data.
 It can store any type of data such as images, videos, text, audio, etc.
Reliability
 A computer is a reliable machine.
 Modern electronic components have long lives.
 Computers are designed to make maintenance easy.
Automation
 Computer is an automatic machine.
 Automation is the ability to perform a given task automatically. Once the computer
receives a program i.e., the program is stored in the computer memory, then the program
and instruction can control the program execution without human interaction.
Reduction in paper work and cost
 The use of computers for data processing in an organization leads to reduction in paper
work and results in speeding up the process.
 As data in electronic files can be retrieved as and when required, the problem of
maintenance of large number of paper files gets reduced.
 Though the initial investment for installing a computer is high, it substantially reduces
the cost of each of its transaction.
Diligence
 Unlike human beings, a computer is free from monotony, tiredness, and lack of
concentration.
 It can work continuously without any error and boredom.
 It can perform repeated tasks with the same speed and accuracy.
Versatility
 A computer is a very versatile machine.
 A computer is very flexible in performing the jobs to be done.
 This machine can be used to solve the problems related to various fields.
 At one instance, it may be solving a complex scientific problem and the very next
moment it may be playing a card game.

HISTORY OF COMPUTER
The history of computer can be classified into generations.
Initially, the generation term was used to distinguish between varying hardware technologies.
Nowadays, generation includes both hardware and software, which together make up an entire
computer system.
There are five computer generations known till date. Each generation has been discussed in
detail along with their time period and characteristics. Following are the main five generations
of computers.
First Generation Computers
The period of first generation was from 1946-1959. The computers of first generation used
vacuum tubes as the basic components for memory and circuitry for CPU (Central Processing
Unit). These tubes, like electric bulbs, produced a lot of heat and the installations used to fuse
frequently. Therefore, they were very expensive and only large organizations were able to
afford it.
In this generation, mainly batch processing operating system was used. Punch cards, paper
tape, and magnetic tape was used as input and output devices. The computers in this generation
used machine code as the programming language.
The main features of the first generation are:
 Vacuum tube technology
 Unreliable
 Supported machine language only
 Very costly
 Generated a lot of heat
 Slow input and output devices
 Huge size
 Need of AC
 Non-portable
 Consumed a lot of electricity
 Example is mainframe computer
Second Generation Computers
The period of second generation was from 1959-1965. In this generation, transistors were used
that were cheaper, consumed less power, more compact in size, more reliable and faster than
the first generation machines made of vacuum tubes. In this generation, magnetic cores were
used as the primary memory and magnetic tape and magnetic disks as secondary storage
devices.
In this generation, assembly language and high-level programming languages like FORTRAN,
COBOL were used. The computers used batch processing and multiprogramming operating
system.
The main features of second generation are:
 Use of transistors
 Reliable in comparison to first generation computers
 Smaller size as compared to first generation computers
 Generated less heat as compared to first generation computers
 Consumed less electricity as compared to first generation computers
 Faster than first generation computers
 Still very costly
 AC required
  Supported machine and assembly languages
 Examples are IBM 1620 and IBM 7094
Third Generation Computers
The period of third generation was from 1965-1971. The computers of third generation used
Integrated Circuits (ICs) in place of transistors. A single IC has many transistors, resistors, and
capacitors along with the associated circuitry.
The IC was invented by Jack Kilby. This development made computers smaller in size, reliable,
and efficient. In this generation remote processing, time-sharing, multiprogramming operating
system were used. High-level languages (FORTRAN-II TO IV, COBOL, PASCAL PL/1,
BASIC, ALGOL-68 etc.) were used during this generation.
The main features of third generation are:
 IC used
 More reliable in comparison to previous two generations
 Smaller size
 Generated less heat
 Faster
 Lesser maintenance
 Costly
 AC required
 Consumed lesser electricity
 Supported high-level language
 Examples are IBM-360 series, Honeywell-6000 series and PDP (Personal Data
Processor).
Fourth Generation Computers
The period of fourth generation was from 1971-1980. Computers of fourth generation used
Very Large Scale Integrated (VLSI) circuits. VLSI circuits having about 5000 transistors and
other circuit elements with their associated circuits on a single chip made it possible to have
microcomputers of fourth generation.
Fourth generation computers became more powerful, compact, reliable, and affordable. As a
result, it gave rise to Personal Computer (PC) revolution. In this generation, time sharing, real
time networks, distributed operating system were used. All the high-level languages like C,
C++, Java, etc., were used in this generation.
The main features of fourth generation are:
 VLSI technology used
 Very cheap
 Portable and reliable
 Use of PCs
 Very small size
 Pipeline processing
 No AC required
 Concept of internet was introduced
 Great developments in the fields of networks
  Computers became easily available
 Example include Super Computers
Fifth Generation Computers
The period of fifth generation is 1980-till date. In the fifth generation, VLSI technology became
ULSI (Ultra Large Scale Integration) technology, resulting in the production of microprocessor
chips having ten million electronic components.
This generation is based on parallel processing hardware and AI (Artificial Intelligence)
software. AI is an emerging branch in computer science, which interprets the means and
method of making computers think like human beings. All the high-level languages like C and
C++, Java, python, .Net etc., are used in this generation.
AI includes:
 Robotics
 Neural Networks
 Game Playing
 Development of expert systems to make decisions in real-life situations
 Natural language understanding and generation
The main features of fifth generation are:
 ULSI technology
 Development of true artificial intelligence
 Development of Natural language processing
 Advancement in Parallel Processing
 Advancement in Superconductor technology
 More user-friendly interfaces with multimedia features
 Availability of very powerful and compact computers at cheaper rates
 Some computer types of this generation are: Desktop, Laptop, NoteBook, UltraBook
and ChromeBook.

BASIC APPLICATIONS OF COMPUTER

Computers play a role in every field of life. They are used in homes, business, educational
institutions, research organizations, medical field, government offices, entertainment, etc.
Home
Computers are used at homes for several purposes like online bill payment, watching movies
or shows at home, home tutoring, social media access, playing games, internet access, etc. They
provide communication through electronic mail. They help to avail work from home facility
for corporate employees. Computers help the student community to avail online educational
support.
Medical Field
Computers are used in hospitals to maintain a database of patients’ history, diagnosis, Xrays,
live monitoring of patients, etc. Surgeons nowadays use robotic surgical devices to perform
delicate operations, and conduct surgeries remotely. Virtual reality technologies are also used
for training purposes. It also helps to monitor the foetus inside the mother’s womb.
Entertainment
Computers help to watch movies online, play games online; act as a virtual entertainer in
playing games, listening to music, etc. MIDI instruments greatly help people in the
entertainment industry in recording music with artificial instruments. Videos can be fed from
computers to full screen televisions. Photo editors are available with fabulous features.
Industry
Computers are used to perform several tasks in industries like managing inventory, designing
purpose, creating virtual sample products, interior designing, video conferencing, etc. Online
marketing has seen a great revolution in its ability to sell various products to inaccessible
corners like interior or rural areas. Stock markets have seen phenomenal participation from
different levels of people through the use of computers.
Education
Computers are used in education sector through online classes, online examinations, referring
e-books, online tutoring, etc. They help in increased use of audio-visual aids in the education
field.
Government
In government sectors, computers are used in data processing, maintaining a database of
citizens and supporting a paperless environment. The country’s defence organizations have
greatly benefitted from computers in their use for missile development, satellites, rocket
launches, etc.
Banking
In the banking sector, computers are used to store details of customers and conduct
transactions, such as withdrawal and deposit of money through ATMs. Banks have reduced
manual errors and expenses to a great extent through extensive use of computers.
Business
Nowadays, computers are totally integrated into business. The main objective of business is
transaction processing, which involves transactions with suppliers, employees or customers.
Computers can make these transactions easy and accurate. People can analyze investments,
sales, expenses, markets and other aspects of business using computers.
Training
Many organizations use computer-based training to train their employees, to save money and
improve performance. Video conferencing through computers allows saving of time and
travelling costs by being able to connect people in various locations.
Arts
Computers are extensively used in dance, photography, arts and culture. The fluid movement
of dance can be shown live via animation. Photos can be digitized using computers.
Science and Engineering
Computers with high performance are used to stimulate dynamic process in Science and
Engineering. Supercomputers have numerous applications in area of Research and
Development (R&D). Topographic images can be created through computers. Scientists use
computers to plot and analyze data to have a better understanding of earthquakes.
LESSON 2
COMPONENTS OF COMPUTER SYSTEM
Computer systems consist of three components as shown in below image: Central Processing
Unit, Input devices and Output devices. Input devices provide data input to processor, which
processes data and generates useful information that’s displayed to the user through output
devices. This is stored in computer’s memory.
Central Processing Unit
The Central Processing Unit (CPU) is called “the brain of computer” as it controls operation
of all parts of computer. It consists of two components: Arithmetic Logic Unit (ALU), and
Control Unit.

Figure 3: Components of Computer System

Figure 4: Central Processing Unit

Arithmetic Logic Unit (ALU)
Data entered into computer is sent to RAM, from where it is then sent to ALU, where rest of
data processing takes place. All types of processing, such as comparisons, decision-making and
processing of non-numeric information takes place here and once again data is moved to RAM.
Control Unit
As name indicates, this part of CPU extracts instructions, performs execution, maintains and
directs operations of entire system.
Functions of Control Unit
Control unit performs following functions:
 It controls all activities of computer
 Supervises flow of data within CPU
 Directs flow of data within CPU
 Transfers data to Arithmetic and Logic Unit
 Transfers results to memory
 Fetches results from memory to output devices
Memory Unit
This is unit in which data and instructions given to computer as well as results given by
computer are stored. Unit of memory is “Byte”. One byte is 8 bits.
Input Devices–Keyboard and Mouse
Input devices help to get input or data from user. Some of input devices are:
Input device Characteristic
Keyboard  The keyboard was the first peripheral device to be used with
computers.
 It helps to input text and numbers into computer.
 It consists of 104 keys and 12 functional keys.
Mouse  A mouse is an input device which is also called as pointing
device because it helps to point data on screen.
 It also helps to select, highlight content and drag-drop controls.
Trackballs  A trackball is also a pointing device which will work like a
mouse. It is mainly used for gaming and entertainment
purpose.
Digital Pens  A digital pen is another input device which is mostly used with
tablets, PDAs, etc.
 A digital pen is also called as a Stylus which helps to write or
draw data over pad.
Scanners  Scanners transform printed material and photographs into a
digital representation.
 After scanning of printed material, page is represented in
memory as an array of pixels.
Barcode readers  Barcode reader helps to read information which is printed as
bars in back of goods or items.
 Barcode readers are most widely used input devices which we
can see in most of products in our day to day life.
 Voice Recognition  Voice recognition system interprets or receives dictation or
System spoken commands to authorize user.
Touch screen  A touch screen is an input device which uses sensors to sense
touch of users to get input data.

KEYBOARD
Keyboard is the most common and very popular input device which helps to input data to the
computer. The layout of the keyboard is like that of traditional typewriter, although there are
some additional keys provided for performing additional functions.

Keyboards are of two sizes 84 keys or 101/102 keys, but now keyboards with 104 keys or 108
keys are also available for Windows and Internet.
The keys on the keyboard are as follows:
S/N Keys Description
These keys include the letter keys (A-Z) and digit keys (0-
1 Typing Keys 9) which generally give the same layout as that of
typewriters.
It is used to enter the numeric data or cursor movement.
Generally, it consists of a set of 17 keys that are laid out
2 Numeric Keypad
in the same configuration used by most adding machines
and calculators.
The twelve function keys are present on the keyboard
which are arranged in a row at the top of the keyboard.
3 Function Keys
Each function key has a unique meaning and is used for
some specific purpose.
These keys provide cursor and screen control. It includes
four directional arrow keys. Control keys also include
4 Control keys
Home, End, Insert, Delete, Page Up, Page Down,
Control(Ctrl), Alternate(Alt), Escape(Esc).
Keyboard also contains some special purpose keys such as
Special Purpose
5 Enter, Shift, Caps Lock, Num Lock, Space bar, Tab, and
Keys
Print Screen.
Output Devices
Output device Characteristic
Monitor  A monitor is most common type of output device.
 It is also called as “Visual Display Unit”.
 The inputs given by keyboard or any other input devices will
get displayed on monitor.
 Cathode Ray Tube (CRT) and Flat panel display monitors are
commonly used monitors.
Printers  Printers are most common type of output devices which are
used to take a hard copy of any digital document.
 The two types of printers are impact and non-impact printers.
 Non-impact printers such as laser and inkjet printers are less
noisy, more reliable and faster and also offer high quality
compared to impact printers.
Sound Systems  Sound systems are output devices which are used to get
multimedia content such as voice, music, etc., as output. Some
of examples of sound systems are speakers, headphones, and
microphones.

PRINTERS
Printer is an output device, which is used to print information on paper.
There are two types of printers:
 Impact Printers
 Non-Impact Printers
Impact Printers
Impact printers print the characters by striking them on the ribbon, which is then pressed on
the paper.
Characteristics of Impact Printers are the following:
 Very low consumable costs
 Very noisy
 Useful for bulk printing due to low cost
 There is physical contact with the paper to produce an image
These printers are of two types -
1. Character printers
2. Line printers
Character Printers
Character printers are the printers which print one character at a time.
These are further divided into two types:
 Dot Matrix Printer (DMP)
 Daisy Wheel
Dot Matrix Printer
In the market, one of the most popular printers is Dot Matrix Printer. These printers are popular
because of their ease of printing and economical price. Each character printed is in the form of
pattern of dots and head consists of a Matrix of Pins of size (5*7, 7*9, 9*7 or 9*9) which come
out to form a character which is why it is called Dot Matrix Printer.
Advantages
 Inexpensive
 Widely Used
 Other language characters can be printed
Disadvantages
 Slow Speed
 Poor Quality
Daisy Wheel
Head is lying on a wheel and pins corresponding to characters are like petals of Daisy (flower)
which is why it is called Daisy Wheel Printer. These printers are generally used for word-
processing in offices that require a few letters to be sent here and there with very nice quality.
Advantages
 More reliable than DMP
 Better quality
 Fonts of character can be easily changed
Disadvantages
 Slower than DMP
 Noisy
 More expensive than DMP

Line Printers
Line printers are the printers which print one line at a time.
These are of two types -
 Drum Printer
 Chain Printer
Drum Printer
This printer is like a drum in shape hence it is called drum printer. The surface of the drum is
divided into a number of tracks. Total tracks are equal to the size of the paper, i.e. for a paper
width of 132 characters, drum will have 132 tracks. A character set is embossed on the track.
Different character sets available in the market are 48 character set, 64 and 96 characters set.
One rotation of drum prints one line. Drum printers are fast in speed and can print 300 to 2000
lines per minute.
Advantages
 Very high speed
Disadvantages
 Very expensive
 Characters fonts cannot be changed

Chain Printer
In this printer, a chain of character sets is used, hence it is called Chain Printer. A standard
character set may have 48, 64, or 96 characters.
Advantages
 Character fonts can easily be changed.
 Different languages can be used with the same printer.
Disadvantages
 Noisy

Non-impact Printers
Non-impact printers print the characters without using the ribbon. These printers print a
complete page at a time, thus they are also called as Page Printers.
These printers are of two types -
 Laser Printers
 Inkjet Printers
Characteristics of Non-impact Printers
 Faster than impact printers
 They are not noisy
 High quality
 Supports many fonts and different character size

Laser Printers
These are non-impact page printers. They use laser lights to produce the dots needed to form
the characters to be printed on a page.
Advantages
 Very high speed
 Very high quality output
 Good graphics quality
 Supports many fonts and different character size
Disadvantages
 Expensive
 Cannot be used to produce multiple copies of a document in a single printing

Inkjet Printers
Inkjet printers are non-impact character printers based on a relatively new technology. They
print characters by spraying small drops of ink onto paper. Inkjet printers produce high quality
output with presentable features.
They make less noise because no hammering is done and these have many styles of printing
modes available. Colour printing is also possible. Some models of Inkjet printers can produce
multiple copies of printing also.
Advantages
 High quality printing
 More reliable
Disadvantages
 Expensive as the cost per page is high
 Slow as compared to laser printer

COMPUTER MEMORY
Computer memory refers to storage area where data is stored. It is of two types:
 Primary Memory
 Secondary Memory
Primary Memory
Primary memory is the main memory of computer present in motherboard. Primary memory is
of two types as shown in the image below.
Random Access Memory
RAM is referred as temporary memory, in which, information stored is lost once computer is
turned off. It is a volatile memory. Instructions written in this memory can be modified; hence
it is also known as programmable memory. The two types of RAM are Static RAM (faster and
costlier) and Dynamic RAM.

Figure 5: Schematic diagram of primary memory

 Figure 6: Diagram of RAM

Functions of RAM
 It stores data till it gets processed.
 It stores instructions for data processing.
 It acts as a working space where data processing takes place and intermediate results
are stored.
 It stores processed data/results before it is sent to output devices.
Read Only Memory
ROM is referred as permanent memory, in which information stored is available even if
computer is turned off. Instructions stored in this memory can only be read and cannot be
modified. Mostly ROM has a start-up instruction which is executed every time when computer
is switched on. Types of ROM are PROM (Programmable Read Only Memory), EPROM
(Erasable PROM), EEPROM (Electrically Erasable PROM) and flash memory.

Figure 7: Diagram of ROM

The below table summarized the major differences between RAM and ROM:
S/N RAM ROM
1. It is volatile memory. It is non-volatile memory.
2. The contents are temporary; data is lost The contents are permanent; data is not
when electricity supply is lost. lost even when power is switched off.
3. Available in small storage capacity. Available in high storage capacity.
4. Processing speed is high. Processing speed is low.
5. User-defined programs can be stored. Generally, operating system supporting
programs can be stored.
6. Cost is very high. Cost effective.
7. It is of two types, SRAM and DRAM. It comes in different types such as
PROM, EPROM, EEPROM and flash
memory.
Secondary Memory
Sometimes when data to be processed is large, it cannot fit in primary memory as it is limited,
in such cases, we use supplement memory or secondary memory. Secondary memory helps to
store information permanently and is non-volatile. Examples of secondary storage memory are
compact disk, floppy disk, pen drive, external hard drive, etc.

CONCEPT OF HARDWARE AND SOFTWARE

The Computing System
The computing system is made up of the computer system, the user and the environment in
which the computer is operated.
The Computer System
The computer system is made up of the hardware and the software. The concept of hardware
and software is explained in detail below:

HARDWARE
The term hardware refers to mechanical device that makes up computer. Computer hardware
consists of interconnected electronic devices that we can use to control computer’s operation,
input and output. Examples of hardware are CPU, keyboard, mouse, hard disk, etc.
Hardware Components
Computer hardware is a collection of several components working together. Some parts are
essential and others are added advantages. Computer hardware is made up of CPU and
peripherals as shown in image below.

Figure 8: Diagram for hardware components

SOFTWARE
A set of instructions that drives computer to do stipulated tasks is called a program. Software
instructions are programmed in a computer language, translated into machine language, and
executed by computer. Software can be categorized into two types:
 System software
 Application software

System Software
System software operates directly on hardware devices of computer. It provides a platform to
run an application. It provides and supports user functionality. Examples of system software
include operating systems such as Windows, Linux, Unix, etc.
Application Software
An application software is designed for benefit of users to perform one or more tasks. Examples
of application software include Microsoft Word, Excel, PowerPoint, Oracle, etc.

Differences between Software and Hardware are sorted out below:

S/N Software Hardware
1. * It is a collection of programs to bring It includes physical components of
computer hardware system into computer system.
operation.
2. It includes numbers, alphabets, It consists of electronic components
alphanumeric symbols, identifiers, like
keywords, etc. ICs, diodes, registers, crystals, boards,
insulators, etc.
3. Software products evolve by adding Hardware design is based on
new features to existing programs to architectural decisions to make it work
support hardware. over a range of environmental
conditions and time.
4. It will vary as per computer and its It is mostly constructed for all types of
built-in functions and programming computer systems.
language.
5. It is designed and developed by The hardware can understand only low-
experienced programmers in high-level level language or machine language.
language.
6. t is represented in any high-level The hardware works only on binary
language such as BASIC, COBOL, C, codes
C++, JAVA, etc. 1’s and 0’s.
7. The software is categorized as The hardware consists of input devices,
operating system, utilities, language output devices, memory, etc.
processor, application software, etc.
Computer users
Computer users are the different categories of personnel that operates the computer. We have
expert users and casual users. The expert users could be further categorized into computer
engineers, computer programmers and computer operators.
The computing environment
The computing environment ranges from the building housing the other elements of the
computing system namely the computer and the users, the furniture, auxiliary devices such as
the voltage stabilizer, the Uninterruptible Power Supply System (UPS), the fans, the air
conditioners etc. The schematic diagram of the computing system is presented in Figure 9a to
Figure 9e.

Figure 9a: Schematic diagram of the computing system

Figure 9b: Computer hardware

Figure 9c: Computer software

Figure 9d: Computer users

Figure 9e: Computing environment

CLASSIFICATION OF COMPUTERS
The computer has passed through many stages of evolution from the days of the mainframe
computers to the era of microcomputers. Computers have been classified based on different
criteria. In this unit, we shall classify computers based on three popular methods.
Objectives
The objectives of this unit are to:
i. Classify computers based on size, type of signal and purpose.
ii. Study the features that differentiate one class of the computer from the others.
Categories of Computers
Although there are no industry standards, computers are generally classified in the following
ways:
Classification based on signal type
 Digital computer
 Analogue computer
 Hybrid computer
Classification by purpose
 Special purpose
 General purpose
Classification by capacity
 Mainframe
 Mini computers
 Micro computers

CLASSIFICATION BASED ON SIGNAL TYPE

There are basically three types of electronic computers. These are the Digital, analogue and
Hybrid computers.
Digital Computer
Represent its variable in the form of digits. It counts the data it deals with, whether representing
numbers, letters or other symbols, are converted into binary form on input to the computer. The
data undergoes a processing after which the binary digits are converted back to alphanumeric
form for output for human use. Because of the fact that business applications like inventory
control, invoicing and payroll deal with discrete values; they are best processed with digital
computers. As a result of this, digital computers are mostly used in commercial and business
places today.
Analogue Computer
It measures rather than counts. This type of computer represents its variables in terms of
electrical voltage and sets up circuit analogue to the equation connecting the variables. The
answer can be either by using a voltmeter to read the value of the variable required, or by
feeding the voltage into a plotting device. They hold data in the form of physical variables
rather than numerical quantities.
In theory, analogue computers give an exact answer because the answer has not been
approximated to the nearest digit. Whereas, when we try to obtain the answers using a digital
voltmeter, we often find that the accuracy is less than that which could have been obtained
from an analogue computer.
It is almost never used in business systems. It is used by the scientist and engineer to solve
systems of partial differential equations. It is also used in controlling and monitoring of systems
in such areas as hydrodynamics and rocketry; in production.
Hybrid Computer
In some cases, the user may wish to obtain the output from an analogue computer as processed
by a digital computer or vice versa. To achieve this, he set up a hybrid machine where the two
are connected and the analogue computer may be regarded as a peripheral of the digital
computer. In such a situation, a hybrid system attempts to gain the advantage of both the digital
and the analogue elements in the same machine. This kind of machine is usually a special-
purpose device which is built for a specific task. It needs a conversion element which accepts
analogue inputs, and output digital value. Such converters are called digitizers. There is need
for a converter from analogue to digital also.
It has the advantage of giving real-time response on a continuous basis. Complex calculations
can be dealt with by the digital elements, thereby requiring a large memory, and giving accurate
results after programming. They are mainly used in aerospace and process control applications.
Examples are MODEM, SIM card etc.

CLASSIFICATION BY PURPOSE
Depending on their flexibility in operation, computers are classified as either special purpose
or general purpose.
Special Purpose Computers
A special purpose computer is one that is designed to solve a restricted class of problems. Such
computers may even be designed and built to handle only one job. In such machines, the steps
or operations that the computer follows may be built into the hardware. Most of the computers
used for military purposes fall into this class. Other example of special purpose computers
include:
 Computers designed specifically to solve navigational problems.
 Computers designed for tracking airplane or missiles.
 Computers used for process control applications in industries such as oil refinery,
chemical manufacture, steel processing and power generation.
 Computers used as robots in factories like vehicles assembly plants and glass industries.
Attributes of Special Purpose Computers
1. Special purpose computer are usually very efficient for the tasks for which they are
specially designed.
2. They are very much less complex than the General-Purpose Computers. The simplicity
of the circuiting stems from the fact that provision is made only for limited facilities.
3. They are very much cheaper than the General-Purpose type since they involve less
components and are less complex.
General-Purpose Computers
General-Purpose computers are computers designed to handle wide range of problems.
Theoretically, a general-purpose computer can be adequate by means of some easily alterable
instructions to handle any problems that can be solved by computation. In practice however,
there are limitations imposed by memory size, speed and the type of input/output devices.
Examples of areas where the general purpose are employed include the following:
  Payroll
 Banking
 Billing
 Sales analysis
 Cost accounting
 Manufacturing scheduling
 Inventory control

Attributes of General-Purpose Computers

1. General-Purpose computers are more flexible than special purpose computers.
2. They can handle a wide spectrum of problems.
3. They are less efficient than the special-purpose computers due to such problems as;
4. Inadequate storage;
5. Low operating speed;
6. Coordination of the various tasks and subsection may take time.
7. General Purpose Computers are more complex than the special purpose ones.

CLASSIFICATION OF COMPUTERS ACCORDING TO CAPACITY

In the past, the capacity of computers was measured in terms of physical size. Today, however,
the physical size is not a good measure of capacity because the modern technology has made
it possible to achieve compactness.
A better measure of capacity today is the volume of work that computer can handle. The
volume of work that a given computer handles is closely tied to the cost and to the memory
size of computer. Therefore, most authorities today accept the price of rental price as the
standard for ranking computers.
Here, both memory size and cost shall be used to rank (classify) computer into three main
categories as follows:
(a)Microcomputers
(b)Medium/Mini/Small Computers
(c)Large Computer/Main Frames.
Micro Computers
Microcomputers, also known as single board computers, are the cheapest class of computers.
In the microcomputer, we do not have a Central Processing Unit (CPU) as we have in the larger
computers rather we have a microprocessor chip as the main data processing unit. They are the
cheapest smallest and can operate under normal office condition. Examples are IBM, APPLE,
COMPAQ, Hewlett Packard (HP), Dell, Toshiba, etc.
Different Types of Personal Computers (Micro Computers)
Desktop personal computers
Normally, personal computers are placed on table desk hence they are referred to as desktop
personal computers. Still other types are available under the categories of personal computers.
They are:
Laptop Computers
These are small size types that are battery-operated. The screen is used to cover the system
while the keyboard is installed flatly on the system unit. They could be carried about like a box
when closed after operation and can be operated in vehicles while on a journey.
Notebook Computer
This is like laptop computers but smaller in size. Though small, it comprises all the components
of a full system.
Palmtop Computer
Palmtop computer is far smaller in size. All the components are complete as any of the above
but made smaller so that it can be held on the palm.
Uses of Personal Computers
Personal computers can perform the following functions:
 Can be used to produce documents like memos, reports, letters and briefs.
 Can be used to calculate budget and accounting tasks
 It can analyze numeric function
 It can create illustrations
 Can be used for electronic mails
 Can help in making schedule and plan projects.
 It can assist in schedules and plan projects.
 It can assist in searching for specific information from lists or from reports.
Advantages of Personal Computers
 Computer is versatile; it can be used in any establishment.
 Has faster speed for processing data.
 Can deal with several data at a time
 Can attend to several users at the same time, thereby able to process several jobs at a
time.
 Capable of storing several data.
 Operating of Computer is less fatigue
 Network possible, that is linking of two or more computers together.
Disadvantages of Personal Computers
 Computer is costly to maintain.
 It is very fragile and complex to handle
 It requires special skill to operate
 With the invention and innovation every day, computer suffers from being obsolete.
  It can lead to unemployment when used mostly in less Developed Countries.
 Some computers cannot function properly without the aid of cooling system e.g. air-
condition or fan in some locations.
Mini Computers
The Mini Computers have memory capacity in the range 128K bytes to 256 Kbytes and are
also not expensive but reliable and smaller in size compare to mainframe. It was first introduced
in 1965; when DEC (Digital Equipment Corporation) built the Personal Data Processor (PDP
– 8). Other Mini Computer includes WANG VS.
Mainframe
The Main Frame Computers often called number crunches have memory capacity of the order
of 4 Kbytes and they are very expensive. They can execute up to 100MIPS (Meanwhile
Instructions Per Second). They have large systems and are used by many people for a variety
of purpose.

INTRODUCTION TO PROBLEM SOLVING TECHNIQUES

Learning Objectives
• To understand the concept of Problem solving
• To understand steps involved in algorithm development
• To understand the concept of Algorithm
• Develop Algorithm for simple problem
• To understand the concept of Flowchart development
• Draw the symbols used in Flowcharts
INTRODUCTION
A computer is a very powerful and versatile machine capable of performing a multitude of
different tasks, yet it has no intelligence or thinking power. The intelligence of a computer
depends on the human intelligence.
In order to instruct a computer correctly, the user must have clear understanding of the problem
to be solved. A part from this he should be able to develop a method, in the form of series of
sequential steps, to solve it. Once the problem is well-defined and a method of solving it is
developed, then instructing the computer to solve the problem becomes relatively easier task.
Thus, before attempt to write a computer program to solve a given problem. It is necessary to
formulate or define the problem in a precise manner. Once the problem is defined, the steps
required to solve it, must be stated clearly in the required order.
PROCEDURE (STEPS INVOLVED IN PROBLEM SOLVING)
A computer cannot solve a problem on its own. One has to provide step by step solutions of
the problem to the computer. In fact, the task of problem solving is not that of the computer. It
is the programmer who has to write down the solution to the problem in terms of simple
operations which the computer can understand and execute.
In order to solve a problem by the computer, one has to pass though certain stages or steps.
They are:
1. Understanding the problem
2. Analyzing the problem
3. Developing the solution
4. Coding and implementation.
1. Understanding the problem: Here we try to understand the problem to be solved totally.
Before with the next stage or step, we should be absolutely sure about the objectives of the
given problem.
2. Analyzing the problem: After understanding thoroughly the problem to be solved, we look
at different ways of solving the problem and evaluate each of these methods. The idea here is
to search an appropriate solution to the problem under consideration. The end result of this
stage is a broad overview of the sequence of operations that are to be carried out to solve the
given problem.
3. Developing the solution: Here the overview of the sequence of operations that was the result
of analysis stage is expanded to form a detailed step by step solution to the problem under
consideration.
4. Coding and implementation: The last stage of the problem solving is the conversion of the
detailed sequence of operations into a language that the computer can understand. Here each
step is converted to its equivalent instruction or instructions in the computer language that has
been chosen for the implementation.

ALGORITHM
Definition
A set of sequential steps usually written in Ordinary Language to solve a given problem is
called Algorithm.
It may be possible to solve to problem in more than one ways, resulting in more than one
algorithm. The choice of various algorithms depends on the factors like reliability, accuracy
and easy to modify. The most important factor in the choice of algorithm is the time
requirement to execute it, after writing code in High-level language with the help of a computer.
The algorithm which will need the least time when executed is considered the best.
Steps involved in algorithm development
An algorithm can be defined as “a complete, unambiguous, finite number of logical steps for
solving a specific problem “.
Step1. Identification of input: For an algorithm, there are quantities to be supplied called input
and these are fed externally. The input is to be identified first for any specified problem.
Step2: Identification of output: From an algorithm, at least one quantity is produced, called for
any specified problem.
Step3 : Identification the processing operations : All the calculations to be performed in order
to lead to output from the input are to be identified in an orderly manner.
Step4 : Processing Definiteness : The instructions composing the algorithm must be clear and
there should not be any ambiguity in them.
Step5 : Processing Finiteness : If we go through the algorithm, then for all cases, the algorithm
should terminate after a finite number of steps.
Step6 : Possessing Effectiveness : The instructions in the algorithm must be sufficiently basic
and in practice they can be carries out easily.
An algorithm must possess the following properties
1. Finiteness: An algorithm must terminate in a finite number of steps
2. Definiteness: Each step of the algorithm must be precisely and unambiguously stated
3. Effectiveness: Each step must be effective, in the sense that it should be primitive easily
convert able into program statement) can be performed exactly in a finite amount of time.
4. Generality: The algorithm must be complete in itself so that it can be used to solve problems
of a specific type for any input data.
5. Input/output: Each algorithm must take zero, one or more quantities as input data produce
one or more output values. An algorithm can be written in English like sentences or in any
standard representation sometimes, algorithm written in English like languages are called
Pseudo Code.

Example
1. Suppose we want to find the average of three numbers, the algorithm is as follows
Step 1 Read the numbers a, b, c
Step 2 Compute the sum of a, b and c
Step 3 Divide the sum by 3
Step 4 Store the result in variable d
Step 5 Print the value of d
Step 6 End of the program

2. Write an algorithm to calculate the simple interest using the formula. Simple interest = P*N*
R/100.
Where P is principle Amount, N is the number of years and R is the rate of interest.
Step 1: Read the three input quantities’ P, N and R.
Step 2 : Calculate simple interest as
Simple interest = P* N* R/100
Step 3: Print simple interest.
Step 4: Stop.
3. Area of Triangle: Write an algorithm to find the area of the triangle.
Let b, c be the sides of the triangle ABC and A the included angle between the given sides.
Step 1: Input the given elements of the triangle namely sides b, c and angle between the sides
A.
Step 2: Area = (1/2) *b*C* sin A
Step 3: Output the Area
Step 4: Stop.
4. Write an algorithm to find the largest of three numbers X, Y,Z.
Step 1: Read the numbers X,Y,Z.
Step 2: if (X > Y)
Big = X
else BIG = Y
Step 3 : if (BIG < Z)
Step 4: Big = Z
Step 5: Print the largest number i.e. Big
Step 6: Stop.

FLOW CHART
A flow chart is a step by step diagrammatic representation of the logic paths to solve a given
problem. Or A flowchart is visual or graphical representation of an algorithm.
The flowcharts are pictorial representation of the methods to be used to solve a given problem
and help a great deal to analyze the problem and plan its solution in a systematic and orderly
manner. A flowchart when translated in to a proper computer language, results in a complete
program.
Advantages of Flowcharts
1. The flowchart shows the logic of a problem displayed in pictorial fashion which felicitates
easier checking of an algorithm.
2. The Flowchart is good means of communication to other users. It is also a compact means
of recording an algorithm solution to a problem.
3. The flowchart allows the problem solver to break the problem into parts. These parts can be
connected to make master chart.
4. The flowchart is a permanent record of the solution which can be consulted at a later time.
Differences between Algorithm and Flowchart
Algorithm Flowchart
1. A method of representing the step-by-step 1. Flowchart is diagrammatic representation
logical procedure for solving a problem of an algorithm. It is constructed using
different types of boxes and symbols.
2. It contains step-by-step English 2. The flowchart employs a series of blocks
descriptions, each step representing a and arrows, each of which represents a
particular operation leading to solution of particular step in an algorithm
problem
3. These are particularly useful for small 3. These are useful for detailed
problems representations of complicated programs
4. For complex programs, algorithms prove 4. For complex programs, Flowcharts prove
to be Inadequate to be adequate

SYMBOLS USED IN FLOW CHARTS

The symbols that we make use while drawing flowcharts as given below are as per conventions
followed by International Standard Organization (ISO).
a. Oval: Rectangle with rounded sides is used to indicate either START/ STOP of the program.

b. Input and output indicators: Parallelograms are used to represent input and output operations.
Statements like INPUT, READ and PRINT are represented in these Parallelograms.

c. Process Indicators: - Rectangle is used to indicate any set of processing operation such as for
storing arithmetic operations.

d. Decision Makers: The diamond is used for indicating the step of decision making and
therefore known as decision box. Decision boxes are used to test the conditions or ask questions
and depending upon the answers, the appropriate actions are taken by the computer. The
decision box symbol is
e. Flow Lines: Flow lines indicate the direction being followed in the flowchart. In a Flowchart,
every line must have an arrow on it to indicate the direction. The arrows may be in any direction

f. On- Page connectors: Circles are used to join the different parts of a flowchart and these
circles are called on-page connectors. The uses of these connectors give a neat shape to the
flowcharts. Ina complicated problems, a flowchart may run in to several pages. The parts of
the flowchart on different pages are to be joined with each other. The parts to be joined are
indicated by the circle.

SIMPLE PROBLEMS USING FLOW CHART

Draw the Flowchart for the following
1. Draw a flowchart to find out the biggest of the three unequal positive numbers.
 2. Draw a flowchart for adding the integers from 1 to 100 and to print the sum.

PSEUDO CODE
The Pseudo code is neither an algorithm nor a program. It is an abstract form of a program. It
consists of English like statements which perform the specific operations. It is defined for an
algorithm. It does not use any graphical representation. In pseudo code, the program is
represented in terms of words and phrases, but the syntax of program is not strictly followed.
Advantages: * Easy to read, * Easy to understand, * Easy to modify.
Example: Write a pseudo code to perform the basic arithmetic operations.
Read n1, n2
Sum = n1 + n2
Diff = n1 – n2
Mult = n1 * n2
Quot = n1/n2
Print sum, diff, mult, quot
End.

DATA COMMUNICATION AND NETWORK

Data communication
Data communications simply refers to a set of computer system that uses telecommunications
for the exchange of data or information.
Data communications are the exchange of data between two devices via some form of
transmission medium such as a wire cable. For data communications to occur, the
communicating devices must be part of a communication system made up of a combination of
hardware (physical equipment) and software (programs).
It is clear from the above that data communication involves an interconnectivity of various
computer hardware in a special way which can be describes as (topology), coupled with some
laid down set of rules and regulation which guides the initiation of data transmission
(protocols). The data transmission process is a function of the medium (communication
channels), speed, direction and mode which is called transmission characteristics.
The data communication architecture is made up of both hardware and software components.
The hardware components includes the following: keyboard, modem, Network Interface Card
(NIC), routers, bridges, and intelligent PC while the software component comprises of the
following: network protocols and operating systems which guides the conversion of digital
codes to electronic signals and vice versa.
Communication channels
Communications channels unite data communication hardware and provide a physical pathway
for the exchange of data. This physical medium is the most critical link in the data
communication system. If the link is broken, the message dies.
Communication channels are built on four basic principles: physical medium, transmission
characteristics, protocol and topology.
Transmission characteristics
The transmission characteristics of the communication channels determine the system’s
performance. These computers can be divided into three functional groups: transmission speed,
transmission direction and transmission mode.
Transmission speed
The transmission speed of a communication channel determines how much data can be
transmitted over the physical medium in a given period of time. This rate is usually measured
in bits per second or bps.
Transmission direction
The transmission direction of a communication channel refers to the ability of the media to
handle simultaneous transmission.
Simplex
In simplex mode, the communication is unidirectional, as on a one-way street. Only one of the
two devices on a link can transmit; the other can only receive. Keyboards and traditional
monitors are examples of simplex devices. The keyboard can only introduce input; the monitor
can only accept output. The simplex mode can use the entire capacity of the channel to send
data in one direction.

Figure 10a. Simplex

Half-Duplex
In half-duplex mode, each station can both transmit and receive, but not at the same time. When
one device is sending, the other can only receive, and vice versa.
The half-duplex mode is like a one-lane road with traffic allowed in both directions. When cars
are traveling in one direction, cars going the other way must wait. In a half-duplex transmission,
the entire capacity of a channel is taken over by whichever of the two devices is transmitting
at the time. Walkie-talkies and CB (citizens band) radios are both half-duplex systems.
The half-duplex mode is used in cases where there is no need for communication in both
directions at the same time; the entire capacity of the channel can be utilized for each direction.

Figure 10b. Half-duplex

Full-Duplex
In full-duplex (also called duplex), both stations can transmit and receive simultaneously. One
common example of full-duplex communication is the telephone network. When two people
are communicating by a telephone line, both can talk and listen at the same time.
The full-duplex mode is used when communication in both directions is required all the time.
The capacity of the channel, however, must be divided between the two directions.

Figure 10c. Full-duplex

Transmission mode
The transmission mode of a communication channel refers to the bit-level organization of the
data and the way it is transmitted over the physical medium. The two common modes of
transmission are asynchronous and synchronous transmissions.
Asynchronous transmission
An asynchronous transmission involves the sending of one character (or byte) at a time. To
separate the characters, a start bit and one or more stop bits are added to each end of the
individual 8-bit character code. This mode of transmission is slow and wasteful because the
system must support 11 bits per byte instead of the standard 8 bits.
Synchronous
A synchronous transmission involves the sending of organized blocks of characters, sometimes
called frames or packets. These packet of data are carefully synchronized so that the sending
and receiving devices can distinguish the boundaries of each character. This mode is faster and
more efficient.

Components
A data communications system has five components.

Figure 11. Components of data communication system

1. Message. The message is the information (data) to be communicated. Popular forms of

information include text, numbers, pictures, audio, and video.
2. Sender. The sender is the device that sends the data message. It can be a computer,
workstation, telephone handset, video camera, and so on.
3. Receiver. The receiver is the device that receives the message. It can be a computer,
workstation, telephone handset, television, and so on.
4. Transmission medium. The transmission medium is the physical path by which a
message travels from sender to receiver. Some examples of transmission media include
twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.
5. Protocol. A protocol is a set of rules that govern data communications. It represents an
agreement between the communicating devices. Without a protocol, two devices may
be connected but not communicating.

Data Representation
Information today comes in different forms such as
 Text
 Numbers
 Images
 Audio, and
 Video
Types of network
There are 3 main types of network
1. Local Area Network (LAN): A LAN is usually privately owned and links the devices
in a single office, building, or campus.

Figure 12. An isolated IAN connecting 12 computers to a hub in a closet

2. Wide Area Network. A wide area network (WAN) provides long-distance transmission
of data, image, audio, and video information over large geographic areas that may
comprise a country, a continent, or even the whole world.
3. Metropolitan Area Networks. A metropolitan area network (MAN) is a network with a
size between a LAN and a WAN. It normally covers the area inside a town or a city. It
is designed for customers who need a high-speed connectivity, normally to the Internet,
and have endpoints spread over a city or part of city. A good example of a MAN is the
part of the telephone company network that can provide a high-speed DSL line to the
customer. Another example is the cable TV network that originally was designed for
cable TV, but today can also be used for high-speed data connection to the Internet.

Interconnecting devices
LANs, WANs, and MANs each speak their own language; the process of connecting multiple
dissimilar systems requires very flexible advanced interconnecting devices, these devices
include:
a. Repeater: Repeaters are simple interconnecting devices that connect two identical
cabling segments of a LAN. A repeater accepts weak signals and electrically
regenerates them and then sends the messages back on their way.
b. Bridges: Bridges are more intelligent than repeaters, they go beyond simply
regenerating weak signals. Bridges process network signals and ensure smooth passage
from LAN to LAN and from LAN to WAN.
c. Routers: Routers contain advanced algorithms that allow them to make intelligent
decisions about where a message should go and what path to use for greater efficiency.
 d. Gateways: Gateways approach interconnectivity from a complete different angle. These
devices use more of software translation than hardware routing. They are required when
network messages travel between two entirely different systems.

Protocols
In computer networks, communication occurs between entities in different systems. An entity
is anything capable of sending or receiving information. However, two entities cannot simply
send bit streams to each other and expect to be understood. For communication to occur, the
entities must agree on a protocol. A protocol is a set of rules that govern data communications.
A protocol defines what is communicated, how it is communicated, and when it is
communicated.
The sole purpose of protocol is to provide guidance to the communication channels and to
promote harmonious connectivity between the many network components. Protocols work on
the electronic level. They are initiated and controlled by advanced subroutines built into each
NIC.
LANs commonly use one of three communications protocols: CSMA, polling and token
passing.
CSMA
CSMA stands for Carrier Sense Multiple Access. CSMA relies on a share trunk of cabling; the
trunk is a single run of cabling that extends throughout the topology of the LAN. Here is how
the protocol works:
1. Workstation A has a message for workstation B. Workstation A listens to the trunk and
waits until all is clear (Carrier Sensing).
2. When A detects that the trunk is clear, the workstation marks the message with a
destination address and sends it over the trunk. All other workstations continually
monitors the trunk for a message with their address (multiple access).
3. Workstation B finds a match, accepts the message and returns an acknowledgement of
receipt.

Polling
Polling refers on a central controlling node (workstation or file server). The central node polls
each station to determine whether there is a message to be sent. When a sending workstation is
ready, the central node reserves the network channel and the message is sent. Polling is
typically used in a centralized system because this type of protocol relies exclusively on the
intelligence and dexterity of the central controlling node.

Token passing
In the token-passing method, the stations in a network are organized in a logical ring. In other
words, for each station, there is a predecessor and a successor. The predecessor is the station
which is logically before the station in the ring; the successor is the station which is after the
station in the ring. The current station is the one that is accessing the channel now. The right to
this access has been passed from the predecessor to the current station. The right will be passed
to the successor when the current station has no more data to send.
But how is the right to access the channel passed from one station to another? In this method,
a special packet called a token circulates through the ring. The possession of the token gives
the station the right to access the channel and send its data. When a station has some data to
send, it waits until it receives the token from its predecessor. It then holds the token and sends
its data. When the station has no more data to send, it releases the token, passing it to the next
logical station in the ring. The station cannot send data until it receives the token again in the
next round. In this process, when a station receives the token and has no data to send, it just
passes the data to the next station.

TYPES OF TOPOLOGY
Type of Connection
A network is two or more devices connected through links. A link is a communications
pathway that transfers data from one device to another.
Point-to-Point
A point-to-point connection provides a dedicated link between two devices. The entire capacity
of the link is reserved for transmission between those two devices.

Figure 13a. Point-to-point

Multipoint
A multipoint (also called multidrop) connection is one in which more than two specific devices
share a single link.

Figure 13b. Multipoint

Mesh
In a mesh topology, every device has a dedicated point-to-point link to every other device. The
term dedicated means that the link carries traffic only between the two devices it connects. To
find the number of physical links in a fully connected mesh network with n nodes, we first
consider that each node must be connected to every other node.
Advantages
 First, the use of dedicated links guarantees that each connection can carry its own data
load, thus eliminating the traffic problems that can occur when links must be shared by
multiple devices.
 Second, a mesh topology is robust. If one link becomes unusable, it does not
incapacitate the entire system.
 Third, there is the advantage of privacy or security. When every message travels along
a dedicated line, only the intended recipient sees it.
 Finally, point-to-point links make fault identification and fault isolation easy.
Disadvantages
The main disadvantages of a mesh are related to the amount of cabling and the number of I/O
ports required.
 First, because every device must be connected to every other device, installation and
reconnection are difficult.
 Second, the sheer bulk of the wiring can be greater than the available space (in walls,
ceilings, or floors) can accommodate.
 Finally, the hardware required to connect each link (I/O ports and cable) can be
prohibitively expensive.
One practical example of a mesh topology is the connection of telephone regional offices in
which each regional office needs to be connected to every other regional office.

Figure 14. Mesh

Star Topology
In a star topology, each device has a dedicated point-to-point link only to a central controller,
usually called a hub. The devices are not directly linked to one another.
Advantages
 Less expensive than a mesh topology.
 Easy to install and reconfigure.
 Far less cabling needs to be housed, and additions, moves, and deletions involve only
one connection: between that device and the hub.
 Robustness. If one link fails, only that link is affected. All other links remain active.
This factor also lends itself to easy fault identification and fault isolation.
Disadvantages
 The dependency of the whole topology on one single point, the hub. If the hub goes
down, the whole system is dead.
 Often more cabling is required in a star than in some other topologies (such as ring or
bus).
 The star topology is used in local-area networks (LANs). High-speed LANs often use
a star topology with a central hub.

Figure 15. Star

Bus Topology
The preceding examples all describe point-to-point connections. A bus topology, on the other
hand, is multipoint. One long cable acts as a backbone to link all the devices in a network.
Nodes are connected to the bus cable by drop lines and taps. A drop line is a connection running
between the device and the main cable. A tap is a connector that either splices into the main
cable or punctures the sheathing of a cable to create a contact with the metallic core.
As a signal travels along the backbone, some of its energy is transformed into heat. Therefore,
it becomes weaker and weaker as it travels farther and farther. For this reason there is a limit
on the number of taps a bus can support and on the distance between those taps.
Advantages
 Ease of installation.
 Redundancy is eliminated. Only the backbone cable stretches through the entire facility.
Disadvantages
 Difficult reconnection and fault isolation.
 A fault or break in the bus cable stops all transmission, even between devices on the
same side of the problem.
Bus topology was the one of the first topologies used in the design of early local area networks.

Figure 16. Bus

Ring Topology
In a ring topology, each device has a dedicated point-to-point connection with only the two
devices on either side of it. A signal is passed along the ring in one direction, from device to
device, until it reaches its destination. Each device in the ring incorporates a repeater. When a
device receives a signal intended for another device, its repeater regenerates the bits and passes
them along.

Figure 17. Ring

Advantages
 Relatively easy to install and reconfigure.
 Fault isolation is simplified. Generally in a ring, a signal is circulating at all times. If
one device does not receive a signal within a specified period, it can issue an alarm.
The alarm alerts the network operator to the problem and its location.
Disadvantages
 Unidirectional traffic.
 In a simple ring, a break in the ring (such as a disabled station) can disable the entire
network. This weakness can be solved by using a dual ring or a switch capable of
closing off the break.

Hybrid Topology
A network can be hybrid. For example, we can have a main star topology with each branch
connecting several stations in a bus topology.

Figure 18. Hybrid

OFFICE APPLICATION SOFTWARE

MICROSOFT EXCEL
INTRODUCTION
Microsoft Excel is a spreadsheet program designed by Microsoft Corporation for spreadsheet
analysis. The spreadsheet is made of columns and rows similar to accounting worksheets. This
program is generally used by all managers, accountants, bankers, cashiers etc. This enable them
to adequately process and manage their daily generated data.
Some of the functions of spreadsheet packages include:
 Ability to perform calculation, with automatic summation facility.
 Ability to update formula cells
 Various formatting facilities to format workbook
 Input data validation strategies
 Chart creations
 Auditing worksheets etc.
Features of MS Excel
 Workbook- A workbook is the file equivalent of the spreadsheet package on which
work is performed and data are stored. The workbook is made up of several worksheets,
which allows various kinds of related information to be organized in a single workbook.
 Active sheet-The active sheet is the worksheet where you are currently working on in
a workbook. The sheet tab of the active sheet is highlighted on the worksheet bar.
 Cell- A cell is the intersection of a row and column. A cell is addressed by using its cell
address e.g. B1, C5, H2 etc.
 Cell address or Reference- The columns in a worksheet are labelled with alphabetic
characters A, B, C, ……, while the rows are labelled with numeric values 1, 2, 3, 4…..
A cell is addressed or referenced by using the column letter with its corresponding row
value e.g. B1, C5, K4, etc.
 Range- A range is a rectangular block of cells. A range can consist of a single cell,
some selected cells, an entire worksheets or all the worksheets in a workbook.
 Range address- A range is identified by its address. A range address or reference
consists of the top left and bottom right cells in the range, separated by two periods or
colon e.g. A1..H20, B2:K4, C5:D8 etc.
 Chart- Charts are used to graphically present data. Reports presented with the aid of
charts are always brief and comparison can easily be made among grouped data. Charts
are of different types (Bar, Pie, Area, Line, etc.) and the choice of any of the chart is
greatly influenced by the type of report to present.
 Chart sheet- This is a sheet in a workbook that contains only a chart. This sheet is
labelled with Chart1, Chart2, Chart3 etc. to distinguish it from worksheets. Chart sheets
are linked to their respective worksheet data and they are updated automatically
whenever changes are made to the source data.
 Formula- Formula is written to perform arithmetic operations such as addition (+),
subtraction (-), multiplication (*), and division (/). The formula is written once and
copied to other cells in return. A formula is preceded by a formula indicator, a symbol
such as “=” e.g. = SUM (E4:F8), =(D4*4)-E2 etc.
 Formula Bar- The formula bar appears at the top of a spreadsheet window, it can be
used to enter or edit values or formulas in cells. In general, content of the active cell is
displayed on the formula bar.
 Operators- Operators are used in a formula to indicate action to be performed on the
arguments (operands). Basic operators in excel include addition (+), subtraction (-),
multiplication (*), division (/) and exponentiation (^).
 Functions- Functions are pre-written (in-built) formulas use to perform some standard
computations. Examples of functions are sum, product, average, maximum, minimum,
sin, standard deviation etc. For example, = SUM(C3:D8) will return the result of
addition of the contents of cell C3 to D8, =SIN(30) return the sin of an angle 30.

HANDS-ON
The students should be introduced to practical in MS Excel such as Formulas, SUM,
Percentage, IF, Nested IF, AND, OR functions etc.
MICROSOFT WORD/WORD PROCESSOR
DEFINITION OF MICROSOFT WORD
This is an application package designed for typing of document and for graphical designing.
Microsoft word belongs to a family called the Microsoft office.
Microsoft office is a program designed by micro-soft companies and has Microsoft attached to
their names. E.g. Microsoft word, Microsoft PowerPoint, Microsoft Excel, Microsoft Access
Etc.
In other words, a word processor is a device or computer program that provides for input,
editing, formatting, and output of text, often with some additional features.

Creating a Document
When a new document is created it has to be formatted to look attractive and presentable. This
determines how the document will look like when finished and printed. The author of the
document could decide to format the document before or after typing.
Steps to Create a blank document
1. Open Word. Or, if Word is already open, select File > New.
2. Select Blank document.
Exercise 1: Type the following passage
New rules to Rationale management;
Foremost: Rationale is the justification of decisions. Rationale models represents the
reasoning that leads to the decisions, including its functionality- and its implementation.
Rationale is critical in two areas: It supports the decisions making and it supports the capture
of knowledge. Rationale includes:
 The issues that were addressed
 The alternatives that were considered
 The decisions that were made to resolve the issues
 The criteria that were used to guide decisions
In the context of decision making the rationale improves the quality of decisions by making
decision elements, such as criteria, priorities, and arguments, explicit. In the context of
knowledge capture, the rationale is the most important information in the development process.
Saving a Document
It is good to cultivate the habit of saving one’s work periodically while typing to avoid loss of
information in case of an interrupted power supply.
To save, follow the steps below:
1. Select File from the Menu
2. Select Save As. A dialogue box appears as shown below:
 3. Select the location to save e.g. desktop, documents etc.

4. Give a name to the document and click the Save button

Some Important Terminology

Soft Return
As you are typing in the document, the moment the cursor gets to the end of the line it
automatically moves to the next line.
Hard Return
This is when the cursor manually moved to the beginning of the next line by pressing the
ENTER key.
Word Art
Use text art to change words in your documents into designs. Word Art designs are graphic
images. They are contained in a graphics box in MS word.
How to Insert WordArt
Word Art is designed to allow you make your text more attractive; you can format your text to
make it look like a picture and enhance its appearance in different ways. The steps to insert
WordArt are given below;
o Place the cursor where you want to insert WordArt
o Select the Insert tab
o In Text group click the 'WordArt' button
o WordArt menu appears;
o Select the desired WordArt style
o 'Edit WordArt Text' dialog box appears
o Type the text in text area and click OK
How to create Drop Cap

A
drop cap (dropped capital) is a large capital letter used as a decorative element at the
beginning of a paragraph or section. The size of a drop cap is usually two or more
lines.
Add a drop cap
1. Select the first character of a paragraph.
2. Go to INSERT > Drop Cap.
3. Select the drop cap option you want.
 To create a drop cap that fits within your paragraph, select Dropped.
 To create a drop cap that is in the margin, outside of your paragraph, select In
margin.

Remove a drop cap

1. Highlight the large drop cap letter.
2. Go to INSERT > Drop Cap, and select None.

MAIL MERGE
Mail merge is an MS word feature that lets you create letters for a number of people without
typing the original letter more than once. The letter is saved in a separate file called form file.
A letter form file contains all the formatting information, text, and graphics you want to be
common to each other. Next you create the data file that contains all the names and addresses
that should go with the letter. Finally, in order to create the complete letters, you merge the
form file with the data file.

Steps to create Mail Merge

1. In a blank Microsoft Word document, click on the Mailings tab, and in the Start Mail
Merge group, click Start Mail Merge.
2. Click Step-by-Step Mail Merge Wizard
3. Select your document type. In this demo we will select Letters. Click Next: Starting
document.
4. Select the starting document. In this demo we will use the current (blank) document.
Select Use the current document and then click Next: Select recipients.
5. Select recipients. In this demo we will create a new list, so select Type a new list and
then click Create.
 Create a list by adding data in the New Address List dialog box and clicking
OK.
 Save the list.
 Note that now that a list has been created, the Mail Merge Wizard reverts to Use
an existing list and you have the option to edit the recipient list.
  Selecting Edit recipient list opens up the Mail Merge Recipients dialog box,
where you can edit the list and select or unselect records. Click OK to accept
the list as is.
 Click Next: Write your letter.
6. Write the letter and add custom fields.
 Click Address block to add the recipients' addresses at the top of the document.
 In the Insert Address Block dialog box, check or uncheck boxes and select
options on the left until the address appears the way you want it to.
 Note that you can use Match Fields to correct any problems. Clicking Match
Fields opens up the Match Fields dialog box, in which you can associate the
fields from your list with the fields required by the wizard.
7. Press Enter on your keyboard and click Greeting line to enter a greeting.
8. In the Insert Greeting Line dialog box, choose the greeting line format by clicking the
drop-down arrows and selecting the options of your choice, and then click OK.
9. Note that the address block and greeting line are surrounded by chevrons (« »). Write a
short letter and click Next: Preview your letters.

LABORATORY EXERCISE
1. The tutor should guide the students in the computer Laboratory on how to generate and
insert automatic table of contents in MS word.

INTRODUCTION TO BASIC
The original BASIC was first developed at Dartmouth College by John Kemeny, Mary Keller,
and Thomas Kurtz and introduced on May 1, 1964. BASIC is short for Beginner’s All-purpose
Symbolic Instruction Code and is an easy-to-understand programming language that was
popular during 1970 – 1980. Today, BASIC is not used to develop programs, but is sometimes
used to help teach the fundamentals of programming.
The BASIC language was originally designed as a simplified version of FORTRAN for use in
teaching programming. From the simple beginnings, the language has grown to become a very
popular multi-purpose language available on a wide variety of machines.
There are many versions of the Basic language:
1. Ms-Basic
2. Gee Whiz-Basic (GW- Basic)
3. QBasic-Quick Basic
4. Just BASIC (JBasic)
5. BASIC Plus
6. BASIC A
7. Turbo BASIC
INSTALLING AND RUNNING JBASIC
Download it here: https://justbasic.com/download.html

ELEMENTS OF BASIC
 Character set
BASIC has the character set consisting of the following elements:
1. Alphabets: A, B, C,….Z (small or capital)
2. Digits: 0, 1, 2……..,9 and
3. Special characters: + – * / ( ) . , $ ; ,: ,= ,> ,< , ^
  Variables
The quantity which may change its values during the execution of the program is called the
variable. A variable is a piece of data kept in the computer's memory (RAM). The location
of a variable in RAM is called the "address."
In QBASIC, variables are also of two types:
i. Numeric variable: Numeric variable can assume numeric value and is represented
by an alphabet or an alphabet followed by another alphabet or digit. For example
A, C, A2, ABC, A6 etc., represent numeric variables.
ii. String/character variable: A string variable is represented by an alphabet
followed by dollar ($) sign. It should be kept in mind that while constructing the
string variable, dollar ($) should be the last character. For example, B1$, NAME$,
BOOK1$, etc. are valid string variables.
 Constants
A quantity in a computer program which does not change its value during the execution of
the program is called a constant. BASIC allows the following constants:
i. Numeric constant: The numeric constant is one that is formed by a sequence
of digits 0, 1, 2,…..9 and may include a decimal point. A numeric constant may
be an integer or a real number. 383, +57, 0, -6.2 and 6.15E4 are valid numeric
constants.
ii. String/character constant: A string constant consists of a sequence of
characters which must be enclosed by a quotation.
 Operator and Operands
Operands are the data or variables on which mathematical, logical and string operations
take place.
Operators are the symbols, which are used in arithmetic operations, logical expressions,
and string expressions.
 Expression
An expression can be a string, or numeric constant, a variable or a combination of constants,
variables with operators which returns a single value.
 Statements
A statement is a set of instructions written using keywords or commands of BASIC. Every
programming language uses keywords as a statement with certain syntax.

BASIC KEYWORDS
1. Remark Statement (REM): This is a remark. It does not affect the program in terms
of instruction or command line. REM: It is used in explaining what the program is all
about.
Example,
10 REM. Program to calculate average of numbers.
This statement will appear as comment on the screen
2. Assignment Statement: This keyword is used in assigning values to variables, e.g.
READ, DATA, LET, INPUT.
 READ statement: This is a statement used in giving values to variables. Usually
READ statement has DATA statement with it.
Example:
10 REM PROGRAM TO SUM NUMBERS
20 READ X
30 DATA 2
40 READ Y
50 DATA 3
60 READ Z
70 DATA 5
80 SUM=X+Y+Z
90 PRINT "The sum is:", SUM
 LET statement: This statement is used in attaching strings of fixed characters and
numeric data in BASIC.
Examples,
10 REM PROGRAM TO SUM NUMBERS
20 READ X
30 DATA 2
40 READ Y
50 DATA 3
60 READ Z
70 DATA 5
80 LET SUM=X+Y+Z
90 PRINT "The sum is:", SUM
 INPUT/ PRINT statements: INPUT statement is used assigning values to variables.
PRINT statement is used displaying values to the screen. The PRINT statement is
usually followed by a list of items to be displayed and each item is separated by a
comma (,) or semi-colon (;).
Example 1:
10 REM PROGRAM TO SUM NUMBERS
20 input "Enter first number:"; X
30 INPUT "Enter second number:"; Y
40 INPUT "Enter third number:"; Z
50 PRINT X, Y, Z
60 PRINT "X=",X,"Y=",Y,"Z=",Z
70 LET SUM=X+Y+Z
80 PRINT "The sum is:", SUM

Example 2:
PRINT 512 + 478
Program output:
990
If you enclose the expression with quotation marks, the expression becomes a string and
isn't evaluated. For example:
PRINT "512 + 478"
Output:
512 + 478

You can use multiple print statements in your program.

PRINT "Hello"
PRINT "World"
Output:
Hello
World

To place World onto the previous line, place a semi-colon after PRINT "Hello".
PRINT "Hello";
PRINT "World"
Output:
HelloWorld

Also, if you put a comma instead of a semi-colon on the first line, the program will insert
spaces between the two words.
PRINT "Hello",
 PRINT "World"
Output:
Hello World

 Program Terminator: These keywords are used to terminate the program, e.g. STOP
and END.
a) STOP statement: This statement is used to terminate a program.
b) END statement: This statement is used to terminate a program.
Example:
10 REM PROGRAM TO SUM NUMBERS
20 input "Enter first number:"; X
30 INPUT "Enter second number:"; Y
40 INPUT "Enter third number:"; Z
50 PRINT X, Y, Z
60 PRINT "X=",X,"Y=",Y,"Z=",Z
70 LET SUM=X+Y+Z
80 PRINT "The sum is:", SUM
90 STOP

Assignments
1. Write a BASIC program to calculate the product of three numbers
2. Write a program to calculate the area of a circle. (Area= πr2)
3. Write a program to calculate simple interest
4. Write a BASIC program to calculate the sum of two numbers
5. Write a BASIC program to find the average of 3 Numbers
6. Write a BASIC program to calculate the area of a triangle with base
7. Write a program to find the product of four numbers using the ‘LET’ statement
8. Write a program to calculate the average of five numbers using the ‘INPUT’ statement

VARIABLES
A variable is a piece of data kept in the computer's memory (RAM). The location of a variable
in RAM is called the "address."
The following program prints the variable X to the screen:
print X
Since the variable hasn't been assigned a number, the value of the variable is 0. So, the output
of the program is:
0
This next program sets X to 15, and then prints the variable:
X = 15
print X
This time, the output is:
15

Also, you can use multiple variables in your program.

X = 82
Y = 101
Z = 79
PRINT X
PRINT Y
PRINT Z
Output:
82
101
79

EXPRESSIONS
If you pass an expression to a variable, the expression is evaluated and the variable is set to
that value.
x = 500 + (10 * 7)
PRINT x
Output:
570

You can also use variables as expressions.

rate = 50
time = 2
distance = rate * time
PRINT distance
Output:
100

Plus, you can have both variables and numbers in an expression.

X = 100
Y=X*7
PRINT Y
Output:
700

STRINGS
If you add a dollar sign ($) to the end of a variable, the variable is a string.
X$ = "Hello World!"
PRINT X$
Output:
Hello World!

A string can be added to the end of an existing variable string.

X$ = "Hello"
X$ = X$ + "World"
PRINT X$
Output:
HelloWorld

You can also add variable strings together.

a$ = "String1"
b$ = "String2"
c$ = "String3"
d$ = a$ + b$ + c$
PRINT d$
Output:
String1String2String3

RECEIVING KEYBOARD INPUT FROM THE USER

One way to receive input from the keyboard is with the INPUT command. The INPUT
command allows the user to enter either a string or a number, which is then stored in a variable.

INPUT data$
PRINT data$
When this program is executed, the INPUT command displays a question mark, followed by a
blinking cursor. And when you enter text, the program stores that text into the variable data$,
which is printed to the screen.
To receive a number, use a non-string variable.
INPUT number
PRINT number

Below is another example of the INPUT command:

PRINT "Enter some text:"
INPUT text$

PRINT "Now enter a number:"

INPUT num

PRINT text$
PRINT text$

CONTROL STRUCTURE
Control structure/statements are used in program to direct the order of execution of the
program. Normally, statements in a program are executed one after the other in the order in
which they’re written. This process is called sequential execution. Various Basic statements,
enable you to specify that the next statement to execute is not necessarily the next one in
sequence. This is called transfer of control. Structured programs are clearer, easier to debug
and modify, and more likely to be bug free in the first place.
Programs could be written in terms of only three control statements:
 the selection statement
 the Jump statement
 the repetition statement.

SELECTION STATEMENT
The selection structure are known as decision making structures. It require that the programmer
specify one or more conditions to be evaluated or tested by the program, along with a statement
or statements to be executed if the condition is determined to be true, and optionally, other
statements to be executed if the condition is determined to be false.
There are three basic types of selection statements:
i. If-then (Single-Selection) Statement
The if statement either performs (selects) an action, if a condition is true, or skips it, if the
condition is false. The if-then statement is the simplest form of control statement, frequently
used in decision making and changing the control flow of the program execution.
Example:
x=5
IF x = 5 THEN PRINT "x equals 5"
Since X does equal 5 in this case, the program outputs:
x equals 5
Expression signs
You can also enter the following statements, instead of the equals sign:
x < 5 (x is less than 5)
x > 5 (x is greater than 5)
Run the following:
x = 16
IF (x > 5) THEN PRINT "x is greater than 5"
Output:
x is greater than 5
You can also combine the signs like this:
x <= 5 (x is less than or equal to 5)
x >= 5 (x is greater than or equal to 5)
x <> 5 (x does not equal 5)
Run the following example:

CLS
x=5
IF (x >= 5) THEN PRINT "x is greater than or equal to 5"
IF (x <= 5) THEN PRINT "x is less than or equal to 5"
IF (x <> 5) THEN PRINT "x does not equal 5"

Output:
x is greater than or equal to 5
x is less than or equal to 5
ii. if-then-else (Double Selection) Statement
The if-then-else statement performs an action if a condition is true and performs a different
action if the condition is false. The if-then single-selection statement performs an indicated
action only when the condition is true; otherwise, the action is skipped. The if-then-else double-
selection statement allows you to specify an action to perform when the condition is true and a
different action when the condition is false.
Using the ELSE command, you can have the program perform a different action if the statement
is false.
x=3
IF x = 5 THEN PRINT "Yes" ELSE PRINT "No"
Output
No

END IF
END IF allows you to have multiple commands after the IF...THEN statement, but they must
start on the line after the IF statement. END IF should appear right after the list of commands.
x=5
IF (x = 5) THEN
INPUT a$
PRINT a$
END IF

The following program uses ELSE with the END IF command:

x = 16
IF (x = 5) THEN
INPUT a$
PRINT a$
ELSE
 PRINT x * 2
END IF

Output:
32

iii. if-then-else-if (Multiple Selection) Statement

The if-then-else-if statement enable us to implement multiple decisions in a program. Basic use
the if-then-else-if command to perform a secondary action if the first expression was false.

Example 1:
x=6
IF (x = 5) THEN
PRINT "Statement 1 is true"
ELSEIF (x = 6) THEN
PRINT "Statement 2 is true"
END IF

Output:
Statement 2 is true
Example 2:
You can have multiple ELSEIF commands, along with ELSE.
x=8
IF (x = 5) THEN
PRINT "Statement 1 is true"
ELSEIF (x = 6) THEN
PRINT "Statement 2 is true"
ELSEIF (x = 7) THEN
PRINT "Statement 3 is true"
ELSE
PRINT "No above statements are true"
END IF
Output:
No above statements are true

Strings in IF...THEN
So far in this chapter, we've only been dealing with numbers, but you can also use strings with
the IF...THEN command.
x$ = "Hello"
IF (x$ = "Hello" OR x$ = "World") THEN PRINT x$

Output:
Hello

You can also compare two variable strings:

x$ = "Hello"
y$ = "World"
IF (x$ <> y$) THEN PRINT x$; " "; y$

Output:
Hello World

JUMP STATEMENT
The GOTO and GOSUB commands enables you to jump to certain positions in your program.
Labels are used to specify what point in the program to continue execution.
GOTO
To use GOTO, place a label somewhere in your program, and then enter.
GOTO <label>
Example
Run the following example program:
PRINT "1"
GOTO TheLabel
PRINT "2"
TheLabel:
PRINT "3"

Output (notice how PRINT "2" is skipped):

1
3

GOSUB
The GOSUB command is the same as GOTO, except when it encounters a RETURN statement,
the program "returns" back to the GOSUB command. In other words, RETURN continues
program execution immediately after the previous GOSUB statement.
PRINT "1"
GOSUB TheLabel
PRINT "2"
END
TheLabel:
PRINT "3"
RETURN

Output (Note: The END command exits the program.)

Since the program returns to the GOSUB command, the number 2 is printed this time.
1
3
2

LINE NUMBERS
"Line numbers" can be used as labels.

PRINT "1"
GOTO 10
PRINT "2"
10 PRINT "3" (Notice the line number)
You can also write the program like this:
10 PRINT "1"
20 GOTO 40
30 PRINT "2"
40 PRINT "3"

The line numbers don't even have to be in sequence.

17 PRINT "1"
2 GOTO 160
701 PRINT "2"
160 PRINT "3"

Each of these programs output:

1
3

GUESSING GAME
The following is a simple guessing game:
CLS
start:
PRINT "Guess a number between 1 and 10: ";
INPUT num
IF (num < 1 OR num > 10) THEN
PRINT "That is not between 1 and 10"
GOTO start
END IF
IF (num = 6) THEN
PRINT "Correct!!!"
ELSE
PRINT "Try again"
PRINT
 GOTO start
END IF

Output (may be slightly different):

Guess a number between 1 and 10: ? 2
Try again
Guess a number between 1 and 10: ? 7
Try again
Guess a number between 1 and 10: ? 6
Correct!!!

REPETITION or LOOP STATEMENT

There may be a situation, when you need to execute a block of code several number of times.
In general, statements are executed sequentially: The first statement in a function is executed
first, followed by the second, and so on. Programming languages provide various control
structures that allow for more complicated execution paths.
Loops make it easier to do an action multiple times. There are at least four types of loops:
 IF...GOTO
 WHILE...WEND
 DO...LOOP, and
 FOR...NEXT

IF...GOTO
This program uses IF...GOTO to create a loop:
x = 10
start:
PRINT x
x = x + 1 (This adds 1 to x)
IF x < 15 THEN GOTO start

Output:
10
11
12
13
14

WHILE...WEND
The WHILE...WEND commands continue a loop until a specified expression is false.
To use WHILE...WEND:
1. Place an expression after WHILE
2. Enter a list of commands
3. Place WEND at the end

Example:
x = 10
WHILE x < 15
PRINT x
x=x+1
WEND

Output (same as in previous example):

10
11
12
13
14

DO...LOOP
DO...LOOP is exactly the same as WHILE...WEND, except it has at least two slight
advantages.
With DO...LOOP you can:
1. Loop until an expression is true
2. Loop at least one time regardless of whether the expression is true or not.
To use DO...LOOP:
1. Specify whether the loop continues "while" the expression is true or "until" the
expression is true, using the WHILE and UNTIL statements, respectively.
2. Place an expression after WHILE/UNTIL
 3. Enter a list of commands
4. Place LOOP at the end
The following uses the WHILE statement:
x = 10
DO WHILE x < 15
PRINT x
x=x+1
LOOP

This program uses the UNTIL statement:

x = 10
DO UNTIL x = 15
PRINT x
x=x+1
LOOP
They both output:
10
11
12
13
14

If you place the expression at the end of the loop instead, the program goes through the loop at
least once.
x = 32
DO
PRINT x
x=x+1
LOOP WHILE x < 5

This is the output because the loop was only gone through one time:
32
FOR...NEXT
FOR...NEXT provides an easier way to create a loop.
Example:
FOR x = 1 TO 5
PRINT x
NEXT x

Output:
1
2
3
4
5
Also, you can use the STEP attribute to specify how much X will be increased each time
through the loop.
FOR x = 1 TO 5 STEP 2
PRINT x
NEXT x

Output:
1
3
5

STOPPING LOOPS
To stop a loop prematurely, use the EXIT command, followed by either FOR or DO.
Example:
FOR x = 1 TO 5
PRINT x
IF (x = 3) THEN EXIT FOR
NEXT x
Output:
1
2
3
(NOTE: This command only works with the DO...LOOP and FOR...NEXT commands, not
with WHILE...WEND or IF...GOTO.)

MATHEMATICS FUNCTIONS
Basic provides several functions to do mathematical calculations. A few of them are discussed
here.
SQR
Use SQR to find the "square root" of a number.
PRINT SQR(1)
PRINT SQR(4)
PRINT SQR(9)
PRINT SQR(16)
PRINT SQR(25)

Output:
1
2
3
4
5

ABS
ABS returns the absolute value of a number. In other words, ABS converts a negative number
to a positive number (if you pass a positive number, ABS does nothing).
PRINT ABS(12)
PRINT ABS(-12)
Output:
12
12
COS, SIN, TAN, and ATN
You can do the following trigonometric functions in QBasic:
COS (Cosine)
SIN (Sine)
TAN (Tangent)
ATN (Arctangent, inverse of TAN)

Example:
CONST PI = 3.141593
PRINT COS(PI / 4)
PRINT SIN(PI / 3)
PRINT TAN(-PI / 2)
PRINT ATN(TAN(-PI / 2))

Output:
.7071067
.8660254
6137956
1.570796 (Same as PI / 2)

ARRAYS
An array is a list of variables of the same type. Arrays are useful for organizing multiple
variables. To create an array, use the DIM (dimension) command.
The following example does not use arrays:
a=2
b=4
c=6
d=8
e = 10
PRINT a, b, c, d, e
Output:
2 4 6 8 10
This uses an array called vars, which contains 5 variables:
DIM vars(5)
Each of these are separate variables:
vars(1) = 2
vars(2) = 4
vars(3) = 6
vars(4) = 8
vars(5) = 10
PRINT vars(1), vars(2), vars(3), vars(4), vars(5)
Output:
2 4 6 8 10

How an array of variables is stored in memory

(NOTE: Memory addresses are not necessarily as specified)

The above program can also be written like this:

DIM vars(5)
FOR x = 1 to 5
vars(x) = x * 2
NEXT
FOR x = 1 to 5
PRINT vars(x),
NEXT

Output:
2 4 6 8 10

STRINGS
You can also create an array of string variables.
DIM vars$(5)
vars$(1) = "Two"
vars$(2) = "Four"
vars$(3) = "Six"
vars$(4) = "Eight"
vars$(5) = "Ten"
PRINT vars$(1), vars$(2), vars$(3), vars$(4), vars$(5)

Output:
Two Four Six Eight Ten

SUBROUTINES AND FUNCTIONS

A subroutine (also called a "module") is a "mini-program" inside your program. In other words,
it is a collection of commands--and can be executed anywhere in your program.
To create a subroutine:
1. Go to the "Edit" menu
2. Select "New Sub"
3. Enter a name for the subroutine
4. Type a list of commands between SUB and END SUB

The following example does not use subroutines:

PRINT "Enter some text:";
INPUT text$
PRINT "The text you entered was: "; text$
PRINT "Enter some text:";
INPUT text$
PRINT "The text you entered was: "; text$

PRINT "Enter some text:";

INPUT text$
PRINT "The text you entered was: "; text$

PRINT "Enter some text:";

INPUT text$
PRINT "The text you entered was: "; text$

PRINT "Enter some text:";

INPUT text$
PRINT "The text you entered was: "; text$

PRINT "Enter some text:";

INPUT text$
PRINT "The text you entered was: "; text$

PRINT "Enter some text:";

INPUT text$
PRINT "The text you entered was: "; text$

By using a subroutine, the above program can be simplified like this:

CALL GetText
CALL GetText
CALL GetText
CALL GetText
CALL GetText
CALL GetText
CALL GetText
SUB GetText
PRINT "Enter some text:";
INPUT text$
PRINT "The text you entered was: "; text$
END SUB

The following is even more concise:

FOR x = 1 TO 7
CALL GetText
NEXT

SUB GetText
PRINT "Enter some text:";
INPUT text$
PRINT "The text you entered was: "; text$
END SUB

FUNCTIONS
A function is the same as a subroutine, except it returns a value. Also, you must leave out the
CALL command.
To return a value, set a variable with the same name as the function.

PRINT Add(10, 7)

FUNCTION Add (num1, num2)

Add = num1 + num2
END FUNCTION

Output:
17
Since a function can return a value, the name of the function can end with special characters
(see Variable types, Using special characters).
' Notice the dollar sign ($) after "Add." It means
' the function returns a string.

PRINT Add$ ("Hello", "World")

FUNCTION Add$ (str1$, str2$)

Add$ = str1$ + str2$
END FUNCTION

Output:
HelloWorld