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HISTORY OF COMPUTING

Luckyboy — Sun, 11 Aug 2013 22:46:00 GMT

History of Computing
• The synthesis of ideas underlying the
general-purpose digital computer was
achieved by Charles Babbage (1791-1871)
• A working model of a "DIFFERENCE
ENGINE” was produced in 1822. It was
steam powered, and calculated
mathematical tables.
2
Charles Babbage
• Babbage then conceived an "analytical
engine" with a storage, an arithmetic unit to
perform calculations, and a punched-card
input and output.
• He spent most of the rest of his life
(unsuccessfully) trying to build and perfect
the machine, which was called by many of
his contemporaries, "Babbage's folly.”
Alan Turing (1912- 1954)
• British Mathematician who did fundamental
work on the theory of modern computer
science.
• Defined a simple but elegant mathematical
model of a general purpose computer, now
called the Turing Machine, and used it to
prove what was possible or impossible for
computers to do. Couldn’t get the money to
build one.
• Today, the ACM’s Turing Award is
considered to be like the Nobel Prize of
computing.
3
COMPUTER GENERATIONS
•THE FIRST COMPUTERS WERE
RESULTS OF WORLD WAR 2
DEVELOPMENTS, AIMED AT MILITARY
USES
•1944 AIKEN AT HARVARD
MARK 1: FIRST ELECTROMECHANICAL
DIGITAL COMPUTER
(ELECTROMAGNETIC RELAYS --
MAGNETS OPEN AND CLOSES METAL
SWITCHES).
THE "FIRST GENERATION:”
VACUMN TUBES
•1946: ENIAC (Electronic Numerical
Integrator and Computer)
•FIRST ELECTRONIC DIGITAL
COMPUTER, CONSTRUCTED WITH
17,000 VACUUM TUBES. EIGHT FEET
TALL AND 80 FEET LONG.
• EXTERNAL (WIRED) PROGRAM.
•ENIAC could do 333 multiplications per
second and cost the equivalent of $5- $10
million

CLASSIFICATION OF COMPUTERS

Luckyboy — Sun, 11 Aug 2013 22:43:57 GMT

CLASSIFICATION OF COMPUTERS
   Computer can be classified based on the way they operate or represent data. On the basis, there are three types, namely:
* Analogue Computer.
* Digital Computer.
* Hybrid Computer.

a. ANALOGUE COMPUTERS: There are computers that are used for measuring changes in physical state of a thing. It represents data in terms of Physical measures or quantities such as temperature, speed, volume and weight. Examples of analog computers and related equipment are car speedometer, measuring scale, thermometer, liquid dispenser (fuel pump) and electric meter, analog wristwatch, aero plane speedometer. etc.

b. DIGITAL COMPUTERS: These are types of computers that are used for counting and calculating. They use discrete forms or binary systems (0s and 1s) to represent data. They store data in terms of digits (numbers). As a matter of fact, anything that counts number produces integers and series of numbers or digits are digit equipment. Examples of digital computer related object are adding machine, calculator, digital wristwatch and hospital thermometer. While examples of digital computers are mainframe, mini computers and micro computers.

c. HYBRID COMPUTERS: These are computers that combine the functions of both analog and digital computers together. They measure and can as well be used for counting and calculation. They exhibit features of analog and digital computers in a single computer system. Hybrid computers are used for complex operations. Hence, many people cannot use them and they cannot be seen easily in the market like the types.

      CLASSIFICATION OF COMPUTER SIZES

    Computer comes in different sizes and shapes. Hence, it is easy to classify computer based on their sizes. Under this classification, computers are grouped into four namely Super computer, mainframe computer, mini computer and micro computer.

These are the biggest, fastest and most expensive types of computer with enormous power and speed. They are also known as "Monsters” or "Maxi” computers. They by scientists for research purposes. They can processes up to a billion instructions per second. Examples are CRAY X/Y models such as Cray X-MP etc.

Features of Super Computers

i. They are the largest and biggest of all computers
ii. They are the fastest known computers.
iii. They are the most powerful.
iv. They use enormous power.
v. They have speed and storage capacity.

Uses of Super Computer

i. They are used for scientific and military applications and researches.
ii. They are used for space exploration, oil exploration, simulations (guessing) and weather forecast.
iii. They are used by large organizations for manufacturing purposes.
iv. They are used for processing large files and performing large scale mathematical calculations.

MINI COMPUTERS: These are mid-sized computers. They are less powerful than the super and mainframe computers. They require less flour space and are easier to install and operate. They can perform many tasks at the same time. Examples are IBM 38, NCR 9300 and MV400.

Features of Mini Computers
i. They are smaller and portable than mainframes.
ii. They are cheaper.
iii. They are used for specific or special purposes.
iv. They have smaller memory.
v. They have lower processing speed and storage capacity than super computer or mainframe computers.
Uses of Mini computers

i. They are used for specific purposes.
ii. They are used by some medium – size companies for manufacturing purposes.
iii. They are used to meet data processing needs such as accounting.
iv. They are used for research purposes.

MAINFRAME COMPUTERS: Mainframe computer are big and fast computers with high processing speed and data storage. They are very expensive. They require a humid environment such as an air conditioned room and a large floor space to function properly. Examples of mainframe computers are NCR – 8800, DBM 360/370 etc.

Features of Mainframe Computers

1. They have very high processing speed but they are slower than super computers.
2. They are less powerful than super computers.
3. They have large memory and storage capacity.
4. They are also very expensive but less expensive than super computers.
5. Mainframe computers accept the connection of large numbers or remote computers.

Uses of Mainframe Computers

i. They are used by large organizations such as banks, universities, research institutes and government establishments for their operations.
ii. They are used by examination bodies such as NECO, WAEC and JAMB (now UTME) to mark students’ scripts and to process results.
iii. They are used for processing large data.
iv. They are useful in large network of individual point of terminal.
v. They are used for updating inventories.

MICRO COMPUTERS
Micro computers are the smallest computers. They are popularly called "Micros” as a result of a component called micro processor contained in their Central Processing Units. They are the commonest computer in all areas of life and the most widely used. They are also called Personal Computers (PC) because they can only be used by one person at a time. There are different types of micro computers depending on their sizes. These include:

1. Desktop Computer: It id placed on the top of a desk or table for use. This is from where it got its name. Desktop computers are the biggest and the commonest types of micro computers. They have very high storage capacity and speed. They support the use of other computer hardware components.

Features of Micro Computers
i. They are smaller than other types of computers.
ii. They are the least expensive.
iii. They are not portable.

2. Laptop Computer: It is called laptop because it can be placed on the laps during use. It can be easily carried about in a special briefcase, thus providing mobile computing technology. It can be either electricity powered. Its greatest advantage is its mobility. That is, it can be carried around. Laptops are costlier than desktop computers.

Uses of Laptop Computers

i. A laptop is mobile and portable.
ii. It is very fast in data processing.
iii. It is useful in all areas of life.
iv. It can be used at anytime because it can be powered with batteries.
v. It is used to watch films and to listen to music,
vi. It used for various data analysis.

Notebook: It is a very light and small PC. It looks like laptop computer but it is small as a textbook. It has all the capabilities of a PC in terms of speed, data processing and storage.

Uses
i. It is used for browsing.
ii. It is used for data processing.
iii. It is portable and convenient to use.
iv. It is useful in listening to music and watching films.
v. It is used for data analysis.
vi. It can be used at any time since it is battery powered.

Palmtop Computer: It is the smallest type of micro computer. It is so small that it can be placed on one’s palm for use. Palmtops are sometimes called "Organizers”. They are also as powerful as the desktop. They have sensitive screen and use electronic writing pad.

Uses
i. It is used for storing addresses and telephone numbers of people.
ii. It is used to keep daily records of one’s activities.
iii. It is used to store important events and dates.
iv. Its soft touch sensitive screen frees users from the constraints of a keyboard.

CLASSIFICATION OF COMPUTER BY GENERATION

From the time of Charles Babbage, there have been several developments in the computer world known as computer generation. There are five generations of computer, namely:

1. FIRST GENERATION COMPUTER: They were built between 1945-1959. These computers were very big, expensive, slow and produced too much heat. The first generation computer used vacuum tubes. Examples are Electronic Numerical Integration and Calculation (ENIAC), Universal Automatic Computer (UNIVAC), EDSAC and EDVAC.

Features of First Generation Computers
i. They are very big and occupied large spaces.
ii. They made a lot of noise.
iii. They had limited storage capacity in magnetic tape.
iv. They were expensive to buy.
v. They generated a lot of heat.
vi. They made use of vacuum tubes.
vii. Punched cards were used to input information.

SECOND GENERATION COMPUTERS: They existed between 1960 – 1965 and used transistors in place of vacuum tubes. Examples are IBM 7090 series, Leo Mark, Atlas and IBM 1401,

Features of Second Generation Computers
i. They were smaller in size and faster than the first generation computers.
ii. They use transistor instead of vacuum tubes as electronic components.
iii. They generated less heat.
iv. They had higher storage capacity.
v. They were less expensive and more reliable than first generation computers.
vi. They required air - conditioning.

THIRD GENERATION COMPUTERS: They existed between 1966 – 1975 and were a great improvement upon the past generations of computers. They used integrated circuits in place of transistors and diodes and were the first generation of computers to use the keyboard, monitor and mouse. Examples are IBM 360 series, CDC 6600 and ICL 1900.

Features of Third Generation Computer
i. They were smaller in size and faster than the second generation computers.
ii. They used integrated circuits (IC) instead of transistor.
iii. They were easy to use.
iv. They had higher storage capacity.
v. They were less expensive.
vi. Monitors and keyboards were introduced as input and output devices.
vii. They made use of high level language.

FOURTH GENERATION COMPUTERS: These are sets of computers were built between 1975 – 1990. Some of them are the micro computer we see today such as desktops and laptops. Their significant characteristics is the development of large – scale integration which implies the combination of many components (more than 100) together.
Features of fourth Generation Computers
i. They have micro processors.
ii. They are smaller in sizes.
iii. They are users friendly and interactive.
iv. They are less expensive and portable.
v. They employ large scale integrated circuits (LSIC).
vi. Air conditioning is not a must for their use.

FIFTH GENRATION COMPUTERS: These are the latest, recent and future generation of computers. They came into existence as from 1990 till date. They use artificial intelligence and are capable of performing many tasks like humans. They involve technological advancements in the field of voice recognition, optical disk, fibre optic networks, internet and virtual reality. They are reliable and can take decisions. Examples are Apple GA, Linux etc.

Features of Fifth Generations Computers
i. They have artificial intelligence (AI).
ii. They have very large scale integrated circuits (VLSI).
iii. They are reliable and can take decisions.
iv. They copy or mimic human senses and perform human activities.
v. They recognize human voice and respond to instructions.

CLASSIFICATION OF COMPUTER BY PURPOSE

Computers can be classified based on the purpose or task they are designed or used for. Based on this, computer can also be classified as:
i. Special Purpose.
ii. General Purpose.

SPECIAL PURPOSE COMPUTERS

A special purpose computer is a computer that is designed to perform one specific function or task. It cannot be used for any other thing. Examples of special purpose computers are home appliances such as MP3 player, washing machine and microwave. Others are airplane control machine, weather forecast machine, automated teller machine (ATM), gasoline dispenser, speedometer, and traffic light system machine.

Features of Special Purpose Computers

Most of them are too bulky and cannot be easily carried from place to place.
i. They require constant power supply.
ii. They are not versatile and can hardly perform any function other than what they were designed to designed to do.
iii. They perform specific task quickly and efficiently.
iv. The output is economical and cheaper.

GENERAL PURPOSE COMPUTERS
A general purpose computer is a computer that is designed from the scratch to do many different tasks depending on the user. All personal computers (micro computers) are general purpose computers.

Features of General Purpose Computers
i. They are very versatile.
ii. They can be easily carried about.
iii. They are not bulky.
iv. They do not require large space to operate. For example, the palmtop computer can be operated on a space as small as the top of the user’s palm.

COMPUTER GENERATIONS

Luckyboy — Sun, 11 Aug 2013 22:30:22 GMT

COMPUTER GENERATIONS
•THE FIRST COMPUTERS WERE
RESULTS OF WORLD WAR 2
DEVELOPMENTS, AIMED AT MILITARY
USES
•1944 AIKEN AT HARVARD
MARK 1: FIRST ELECTROMECHANICAL
DIGITAL COMPUTER
(ELECTROMAGNETIC RELAYS --
MAGNETS OPEN AND CLOSES METAL
SWITCHES).
THE "FIRST GENERATION:”
VACUMN TUBES
•1946: ENIAC (Electronic Numerical
Integrator and Computer)
•FIRST ELECTRONIC DIGITAL
COMPUTER, CONSTRUCTED WITH
17,000 VACUUM TUBES. EIGHT FEET
TALL AND 80 FEET LONG.
• EXTERNAL (WIRED) PROGRAM.
•ENIAC could do 333 multiplications per
second and cost the equivalent of $5- $10
million
4
SECOND GENERATION
•USED SEMICONDUCTOR TRANSISTOR
CHIPS DEVELOPED AT BELL LABS
•1955 : IBM COMPUTER WITH 2000
TRANSISTORS. BY 1959, DELIVERIES
MADE THE VACUMN TUBE
COMPUTERS OUTMODED. INCLUDED
VERY LARGE MAINFRAMES, SUCH AS
THE IBM 7090, AND SMALLER
MACHINES, SUCH AS THE IBM 1401.
THIRD GENERATION
•THE DISTINCTION AMONG
SUBSEQUENT GENERATIONS IS NOT
AS CLEAR AS THAT BETWEEN THE
FIRST AND SECOND GENERATION
COMPUTERS.
•THIRD GENERATION IS
CHARACTERIZED BY THE ABILITY TO
SUPPORT MULTI-PROGRAMMING.
COMPUTERS THAT USE INTEGRATED
CIRCUIT TECHNOLOGIES ARE PART OF
THE THIRD GENERATION (LSI, OR
LARGE SCALE INTEGRATION).
5
THIRD GENERATION
•AS PART OF THE THIRD GENERATION,
WE ALSO SAW THE EMERGENCE OF
"MINI-COMPUTERS”-
•1968 DEC-- FIRST MINI
•1972 IBM 370 SEMI-CONDUCTOR
MEMORY CHIPS
•60’S AND 70’S PUNCH CARD & BATCH
PROCESSING STILL DOMINANT.
Applications and Impacts
• Through the first three generations of
computers (40’s 50’s and 60’s) they were
used almost entirely for business (payroll and
inventory), government, and scientific
computing.
• Punch cards and batch processing.
• In the 1970’s, integrated circuits began to to
make computers smaller and cheaper.
• 1974- first "personal computers” sold as kits
• 1977 Wozniak and Jobs released the Apple
II (first mass marketed PC)
6
FOURTH GENERATION
•NO GENERALLY ACCEPTED
DEFINITION OF FOURTH GENERATION.
SOME SAY IT IS THE VLSI (VERY
LARGE SCALE INTEGRATION) SUPERCOMPUTERS.
•SOME SAY IT IS THE EMERGENCE OF
THE MICROCOMPUTER IN THE FORM
OF PERSONAL COMPUTERS AND WORK
STATIONS.
1983 JAPANESE ANNOUNCE
"5TH GENERATION” PROJECT
•COMPUTERS THAT WILL TAKE
SPEECH INPUT AND OUTPUT, IN
"NATURAL LANGUAGE”
•"Easy to use” computers require tremendous
speed. By the end of the 20th century, speeds
are measured in MIPS- millions of
instructions per second. Many computers now
do 1000 MIPS ( a billion instructions/sec)

Computer Software

Luckyboy — Sun, 11 Aug 2013 22:23:41 GMT

Computer Software
Software is the set of instructions, often called a program that controls the operation of a computer system. It tells the computer what to do, how and when to do it.
Software can be specially developed for a particular field such as education, entertainment, communication, networking, utility etc. People that develop software are often called Programmers

Types of Software

A. System software: A specialized program that coordinates and controls the basic internal operation or function of the computer system. They also enable application software or other programs to run properly, for example operating system (Window 2000, Window Xp).
B. Application Software: This allows the user to perform a specific task on the computer. They are ready – made program written in a standardize form packages and widely available which can be bought off the shelf in a computer shop. For example Microsoft word, Corel Draw, Adobe Photoshop. Etc.

Examples of Computer System Software

1. Microsoft Disk Operating System (MS-DOS): This is one of the earliest operating system software used on personal computers. It is command driven because; it requires the user to instruct the computer. For instance, the user type Cls as command to clear the screen.
2. Graphic User Interface (GUI) Operating System: Example is a Window which is the most popular operating system in use today and comes ready with personal computers. Windows use graphics and icons to represents objects and it is usually driven by a computer mouse.
3. Macintosh Operating System (Mac OS): This is the operating system used in Apple Macintosh computers. It is similar in nature as the window operating system that runs on the PC.

Application Software

* Word Processing Software: Used for typing and producing neat, accurate and professional documents; for example Microsoft Word, Word Perfect. etc.
* Desktop Publishing Software: Used to produce books, posters documents etc. for example Corel Draw.
* Presentation Software: This can be used to present ideas for others in a pictorial manner; such presentations can be in form of Seminars, Workshops, and Lectures. Etc. and example of a presentation software is Microsoft Power point.
* Entertainment Software: These are used to educate and entertain users. Game program fall in this category. For example Pinball, solitaire, Dangerous Dave, Zuma etc.
* Communication Software: Software that makes it possible for people to communicate together. Examples are Microsoft Outlook, Mozilla Firefox, Internet Explorer, Netscape Navigator, Maxthron, Sea Monkey etc.
* Networking Software: This is the software used for many computers to communicate across a network and share resources. An example is Window New Technology. (NT)
* Utility Software: These are softwares used to enhance the smooth performance of your computer operation. They can be used to detect problems on the Computer and possibly to resolve them. Examples are antivirus program, file Management program, security etc.

Number Bases

Luckyboy — Sun, 11 Aug 2013 22:21:40 GMT

Number Bases
The Arithmetic and Logical Unit (ALU) and related operations. ALU can add, subtract, multiply and divide numbers.
       The number of digits in a particular number system is called the BASE.
The four (4) numbering system commonly used with micro computer are the binary, octal, decimal and hexadecimal. The binary numbering system uses only two digits i.e. zero (0) and one (1). The octal numbering system is the base 8 numbering system and the digits involved are 0,1,2,3,4,5,6 and 7.
The decimal numbering system is the base 10 numbering system. The digit involved are 0,1,2,3,4,5,6,7,8 and 9.
The hexadecimal or the base 16 numbering system has sixteen digit namely 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F. The letter A,B,C,D,E,F represent the natural numbers i.e. 10, 11, 12, 13, 14, 15 respectively. The base written as a subscript and enclosed in bracket. For example the 1101(2), 6573(8), 8963(10) and   63AD (16) are written in the base 2, 8, 10 and 16 respectively.

Conversion of Numbers in base (2) to number is base (10)
2000 + 400 + 50 + 6
i.e. (2 * 1000) + (4 * 100) + (5 * 10) + (6 * 1)
i.e. (2 * 103) + (4 * 102) + (5 * 101) + (6 * 100)
Note that the value of a number raised to power zero is one. I.e. 100 =1,20 =1, 80 =1 etc.
For example, the expanded form of the number 1101(2) then become (1 * 23) + (1 * 22) + (0 *21) + (1 * 20). To convert a number in base 2 to a number in base 10(ten), we simply write the given base 2 number in an expanded form and solve the problem.

Solve the following examples
Convert the following base 2 number to base 10(ten).
A. 1101(2) B. 11111(2) C. 110111(2)

Operating System

Luckyboy — Sun, 11 Aug 2013 22:17:05 GMT

Operating System
Definition of Operating System
Operating system can be referred to as Os, it is the software that controls the basic internal operations of a computer system, and coordinates the hardware activities. The operating system is the first program that is loaded whenever the computer is turned on; it provides the platform on which other applications programs will run. It is sometimes regarded as the supervisor. The operating system usually resides insides the computer (memory and hard disk) and is very important to the computer system such that without it, the computer will not work.

Examples of Operating System

* Microsoft Disk Operating System (MS-DOS)
* Graphic User Interface Operating System (GUI) e.g. Window 98, Window 2000, Window Xp etc.
* Macintosh Operating System (Mac Os)
* Linux – Examples of an operating system that allows multiple users to use the computer at the same time or different time.
* UNIX – This is a version of the Unix Operating System.

Functions of Operating System

* It tells the computer processor how to operate.
* It co-ordinates hardware and software activities.
* It controls the input and output such as keyboard, mouse, joystick, monitor, and printer function etc.
* It supervises the smooth running of the application software such as typing of documents using Ms-Word.
* It passes control from one program to the other; for example, when working on two programs at the same time such as Ms Word and Ms Excel.
* Resource Sharing: e.g. sharing of printer on a network.
* Memory management: The Operating System allocates adequate memory for running a particular program.
* Storage/File management Operating System manages how files are stored in floppy disk, hard disk, flash disk, compact disk.

Introduction to Computer Programming

Luckyboy — Sun, 11 Aug 2013 22:15:02 GMT

Introduction to Computer Programming
Programming involves writing the instructions to enable a computer to do a specific task. These instructions have to be written according to the rules of the particular programming language chosen for the task.

Principles of good Programming

The aim of computer programming is to transform a description of a user’s problem and an approach to its solution into form whereby it may be executed by a computer. The principles include:
* Simplicity: The programmer language enables the programmer to state the computational solution to a specified problem in a notation which is both formal and human-intelligible.
* Portability: The programming language is machine independent. Program can be written without prior knowledge of the machine on which they are run. Also, having run on one machine, they can be transported to run on other machines.
* Accuracy: The program must do what it is supposed to do correctly and must meet the criteria laid down in its specification.
* Reliability: The program must do what it is supposed to and never crash.
* Efficiency: This is optimal utilization of resources. The program must use available storage space and other resources in such a way that the system speed is not wasted.
* Usability: The program must be easy enough to use and be well documented.
* Maintainability: The program must be easy to amend having good structuring and documentation.
* Readability: The code of the Program must be well laid out and explained with comments.
* Documentation: User manuals – consisting statements given about the entire program.

FORTRAN LANGUAGE

Luckyboy — Sun, 11 Aug 2013 22:13:17 GMT

FORTRAN LANGUAGE
CLASSES OF DATA
Computer programs, regardless of the language in which they are written, are designed to
manipulate data of some kinds. CONSTANTS and VARIABLES, and their terms are used in
FORTRAN in almost the same sense as in mathematics.
CONSTANTS
A constant is a quantity whose value does not change during program execution. It may be of
numeric, characters, or logical type.
INTEGER CONSTANTS - A is integer constant is literally an integer, i.e., a whole number
without a decimal point. It may be zero or any positive or negative value.
RULES FOR FORMING INTEGER NUMBERS
1. No decimal point
2. No fractional values.
3. Used as counter, exponents and identification number.
4. Results of integer arithmetic reduced to next-lower integer.
5. In general, the maximum magnitudes is 231- 1 a 10 digit number (depending on
computers but some used 9 digits)
6. Remainders resulting from division are lost or truncated.
14/3 value is 4
5/6 value is 0
19/5 value is 3
7. No commas are to be included in a string of digits.
8. Spaces with a constant are allowed but their use is discouraged as it is error prone
9. The minus sign must precede a negative constant, a plus sign is optional and an unsigned
constant is considered positive.
Example:- 25 0 -7 +15274
But the following are not valid integer constants.
18.0 Contains a decimal point
- .284 Contains a decimal point
10,235 Contains a comma
--7 Not preceded by a single algebra
12345678995 Too large.
REAL CONSTANT – Also called a floating points constant, is a constant with a decimal point
and may have a fractional part.
Examples: 18.3 -163.0 42.0 4.0125 (they are all valid)
While the followings are invalid
1,465.3 Contains a comma
-56 Contains no decimal point.
RULES FOR FORMING REAL CONSTANT
1. Decimal point must be included
2. Should not be used as an exponent for integer numbers.
3. Remainders resulting from division are not lost.
4.Ø/3.Ø Value is 1.3333333
4.Ø/5.Ø Value is Ø.8ØØØØØØ
17.Ø/5.Ø Value is 3.4ØØØØØØ
Ø.5e2/ Ø.2E1 Value is 25. ØØØØØØ
Other types of constant are double precision and complex but they are not treated here.
VARIABLES
A variable name, or simply variable, is a name used to identify data stored in a memory location
whose contents may change during program execution.
Integer Variable Name:– A variable beginning with any of the letters I, J, K, L, M, N is
assumed to be an INTEGER Variable.
Real-Variable Names: – A variable beginning with any letter except I, J, K, L, M or N is
assumed to be a REAL Variable.
RULES FOR FORMING VARIABLE NAMES
1. First character must be a letter
2. Subsequent letters may be any combination of letters and digits (other characters
cannot be used).
3. Variable names must not exceed six characters (for most computers)
4. Integer-Variable names must begin with letters l to N only.
5. Real variable names must begin with any other letter (A-H or O-Z)
6. Blank spaces may be inserted to improve readability and do not count as one of the
six allowable characters.
7. The same name must not be used for more than one variable in a given program.
8. Before a variable name can be used in computation, it must be assigned a numerical
value by an assignment statement, READ statements, or a DATA statement.
9. Term that are part of the FORTRAN vocabulary e.g. READ, WRITE, REAL, IF,
(reserved words should not be used as variable names.
Integer variable names Real Variable names
Designator I, J, K, L, M,N A-H, O to Z
NUMBERS NUM NO RADIUS RAD R
MAN 1 MOL M AREA ARC A
ITEMS JOHN J CIRCUM CIR C
NUM 1 LAGOS KILO2 TIM T1 T2
The following are invalid variable name.
KONTAGORA exceeds 6 characters
READ FORTRAN Reserved word
KILO –1 Contains – (hyphen)
TIME .T Contains special character not a letter.
OPERATIONS
Numeric data can be manipulated using arithmetic operations, character data using concatenation
and substring operations, and logical data using logical data using logic operation. When
referring to a combination of variables and constants together with operation symbols, we use the
phrase expression.
Arithmetic Operation
The following six arithmetic operations are available in FORTRAN.
1. Addition
2. Subtraction
3. Multiplication
4. Division
5. Exponentiation
6. Negation
The first five arithmetic operations are all binary operations in the sense that two operations are
required while the last operation is called Unary operation because only one operand is required.
E.g. To indicate the negation of a variable X write.
-X or (-X).
When two constants or variable of the same type are combined, using one of the four arithmetic
operations (+, -, *, /) the result will be of the same type as the operands.
For example, the sum, difference and product of the integers 8 and 6 will be the integers 14, 2
and 48 respectively. Integer division in FORTRAN, say, evaluation 15/4 yields instead of 3.75,
5/6 yields Ø and –5/2 yields –2 (these are all integral part of the quotient. The fractional part of
the quotient is deleted simply because the results are real in value.
It is also possible to combine an integer quantity with a real quantity, using the four arithmetic
operations (+, -, *, /). Whenever one of the operands of operations is an integer and the other
real, the integer is automatically converted to its real equivalent, and the result is of real type.
Thus,
5. + 4 = 5. + 4. = 9.
5. + 3 = 5.* 3. = 15
5./4 = 5./4 = 1.25
Such operations involving different types of numeric operands are called mixed –mode
operations.
The manner in which exponentiation is performed depends upon the type of the exponent. E.g.
2* *3 = 2* 2*2 = 4 * 2 = 8
1.5 * *2 = 1.5 * 1.5 = .25
(-3.Ø) * * 2 = (-3.Ø) * (-3.Ø) = 9. Ø
But, if the exponents is a real number the exponentiation of any constant/number, integer or real,
is computed using logarithms and hence, since logarithms of negative values are not defined, the
negative number raised to a real power is undefined. Thus, even through
(-3.Ø) * * 2 yields the value 9. Ø, (-3.Ø) * * 2 .Ø – exp (2. Ø log (-3.Ø)) is undefined, since log
(-3.Ø) is not defined.
PRECEDENCE – This specifies the order in which the arithmetic operations are to be carried
out.
ORDER
1st parentheses
2nd function
3rd Exponentiation
4th Multiplication/Division (any one met first)
5th Addition/Subtraction (any one encountered first)
Unary plus and minus on the same level as binary addition and subtraction, that is, -2.2* *2
means – (2.2 * * 2) which yields –4.84
Examples.
Mathematical expression: ab3 + d- e
CosC
FORTRAN expression: A* B * * 3/ cos (c) + D – E
Assuming: A = 2.0, B = 3.0, c = 0.0, D = 4.0 E= 5.0
2.0 * 3.0 * * 3/Cos(0.0) + 4.0 – 5.0
(1)
(2)
27. Ø
Mathematical expression: a + b
(c + d) Sin2 (PI/b)
FORTRAN EXPRESSION: (A + B) / (C + D ) * SIN (PI/B)**2
Assuming: A= 4.0, B = 6.0, C = 2.0, D = 3.0, PI = 3.141593
Then, the expression is evaluated in FORTRAN as
( 4.0 + 6.0) / (2.0 + 3.0) * SIN (3.141593/6.0) **2
(a) X23 (b) (X2)3
FORTRAN expression (a) X * * 2 * * 3 (b) (X * * 2) * * 3
Let X = 5.0
The FORTRAN expression will be:
(a) 5.0 * * 2 * * 3
(b) (5. Ø * * 2) * * 3
CONCATENATION
This is a binary operation. This operation is denoted by the symbol // (double slash) and can be
used to combine two, or more, character strings, and /or character variable e.g.
‘UN’ // ‘AAB’
Produces the character string
UNAAB
Again, if CHARACTER * 7 MODEL (here the 7 indicates 7 spaces)
And MODEL is set to ‘IBM – 360’
Then MODEL // ‘com’// "PUTER”
Yield the character string
‘IBM – 360 COMPUTER’
SUBSTRING
This is a binary operation requiring only one operand. This is performed on character strings to
extract a sequence of consecutive characters from a string. Such a sequence is called a substring
of the given string.
The general form is
STRING (i:j)
Where i and j are positive integer constants, variables, or expressions such that i < j. The default
value for i and j are 1 and the last position in the character string respectively.
Examples
CHARACTER * ll COURSE
And set course to ‘MATHEMATICS’, then
COURSE (:5) will yield ‘MATHS’
And COURSE (6: ) WILL YIELD ‘MATICS’
Again,
COURSE (M: M + 2) if M is assigned the value 3, has the value
‘THE’
Care must be taken to ensure that i is not greater than the number of characters in the character
string. The value for j should be such that the sequence of characters from i through j does not
extend beyond the last character in the character string.
Substring names may be used to form character expressions just as character variables are used.
They may be concatenated with other character values as in
X (NAME (i:i). LT. ‘A’) PRINT * ‘ILLEGA NAME)
LOGICAL OPERATIONS
The logical variables, or constants may be combined, using the three basic logical operations,
AND., OR., and .NOT.
Examples:
A. .LT. B .AND. C .GT. D
i.e. Is A less than B and is C greater than D?. The .AND. requires that both conditions be
satisfied for the expression to be true. The .OR. operator is used as follows.
E .GE. F .OR. G .LE. (H – X)
i.e is E greater than or equal to F or is G less than or equal to the value of H minus X ? The .OR.
means that when either condition is true, the expression is true.
An example of an INCORRECT logical expression is
A. .AND. B .LT. C
because logical operations . AND. and .OR. relate logical expressions, not individual variable
name.
Logical Expressions
Logical Meaning
Expression
A. LT. B Is A less than B?
C. EQ. (D/E) Is C equal to the quotient of D divided by E
X .GT. (R + S) Is X greater than the Sum of R and S.
8.3 FUNCTIONS
FORTRAN provides a number of program modules, or built-in functions that performs such
mathematical functions. These built-in functions are termed INTRINSIC FUNCTIONS. The use
of an intrinsic function is specified by writing the function name followed by the expression to
be operated upon (the argument) inside a set of parentheses. e.g.
The FORTRAN expression of
X = .y is X = SQRT (Y)
X = |Y – a| is X = ABS|Y – A|
X = e y + a is X = EXP(Y + A)
X = max(a,b,c) is X = AMAXI(A,B, C)
FORTRAN STATEMENT
ASSIGNMENT STATEMENT
This is used to assign values to variables and has the form
Variable = expression.
Where expression may be a constant, another variable to which a value has previously been
assigned, or a formula which the computer can evaluate.
The ‘equals’ i.e. ‘=’ in the assignment statement is not interpreted the same sense as in
mathematics but must be read as "is assigned”. Thus A =B is not the same as B = A since the
first assigns B to A while the latter assigns A to B leaving B unchanged.
This can be interpreted as A B and B A respectively.
Consider the assignment Statement
SOLA = SOLA + BUNMI
This instructs the computer to add to the value of the variables SOLA the value of the variable
BUNMI and assign the result as the new value of the variable SOLA. If SOLA and BUNMI
contains.
SOLA BUNMI
8.0 16.0
SOLA = SOLA + BUNMI
SOLA = 8.0 + 16.0
SOLA = 24.0
SOLA
24.0
The former content of SOLA (i.e. 8.0 is destroyed after the assignment statement given way to
the new value 24.0.
The variable to be assigned a value must appear on the left of thee equal sign and that a legal
expression appears on the right of the equal sign in the assignment statement.
The following are invalids.
18 = M Variable M is on the right hand instead of the left hand
X + 4.3 = 3.14 Numeric expression should not appear to the left of equal sign.
STRING = 4118 The number 4118 is an illegal expression
A = B = 7 B = 7 is an illegal expression
C = ‘3’ * ‘9’ ‘3’ * ‘9’ is an illegal expression
STRING = 10 numeric value 10 is assigned to a character
M = ‘10’ a character constant ‘10’ is assigned to a numeric variable
ASSIGNMENT TO NUMERIC VARIABLES
When assignment statement is used to assign value to a numeric variable, it must take care of the
type of the numeric variable and the value assigned to the variable.
If an integer-value expression is assigned to a real variable, the value is converted to a real
constants and then assigned to the variable e.g. if N = 10
Y = 3
X = (N + 5) / 5.0
Assigns the real constant 3.0 to X and real constant 3.0 to Y
If a real expression is assigned to an integer variable, the fractional part is truncated and the
integer part is assigned to the variable. E.g. If X = 7.41 and I, J, K are all integer variables, then,
I = 3.14159
J = X/3.
K = 1./3. + 1./3
Would assign the integer constants 3, 2 and 0 to the variables I, J and K respectively.
ASSIGNMENT TO CHARACTER VARIABLES
It must take care of the length associated with it. e.g.
CHARACTER* 6 STRNGA, STRNGB* M .TRVN, PAD
STRNGA = ‘VRMILA’
STRNGB = STRNGA // ‘AGRAWAL’
From here, there are 6 character (spaces/ length) assigned to STRNGA, TRVN, and PAD while
STRNGB is assigned 14 characters.
The values ‘URMILA’ and ‘VRMILA’ ‘AGRAWAL’ are assigned to STRNGA and STRNGB
respectively.
Here the declared length of the variables is greater than the length of the value being assigned,
values are padded with blanks. Conversely, if the declared length of the variable is less than the
length of the value being assigned, the value is truncated to the size of the variable and the
leftmost characters are assigned. Thus the statement
PAD = ‘JOY’
Will assign the value ‘JOYbbb’ to the variable PAD, where b denotes blank, and the statement
TRUN = ‘COME – AGAIN’ assigns
The value ‘COME-A‘ to the variable TRUN
INPUT AND OUTPUT STATEMENTS
FORTRAN provides two types of input/output (I/O) statements; formatted and list-directed
(Unformatted, or format-free). In the case of formatted, the programmer must specify the format
in which the data is input, or, output. But in the case of unformatted, certain predetermined
formats which match the types of items in the input/output list are automatically provided by the
compiler.
LIST DIRECTED INPUT STATEMENT.
It is of the form
READ *, V1, V2, V3, ... Vn
Where V1 refers to the first input data item, V2 to the second and so on. The variable names must
be separated by commas. The space between READ and * is optional. Additional spaces may be
inserted between a comma and a variable name.
Example:
READ *, ADE, OLU, JOHN.
READ * KOLA
READ* A, B, C or
READ* A
READ* B
READ* C
Another way by which READ statement (without a Format) is coded as
READ (* *) V1, V2 ............... Vn
The first asterisk indicates that the data are to be manually keyed in via keyboard. The second
asterisk indicates that the data supplied will be unstructured (without FORMAT specification).
V1, V2 ............... Vn represents the lists of variable names to be read
E.g. READ ( * , *) ADE, OLU
READ (* ,*) OJO
LIST DIRECTED OUTPUT STATEMENT
It is of the form
PRINT *, V1, V2 ... Vn
The same rules that apply to READ is also applicable to PRINT.
Another way by which list-Directed WRITE statement can be output is
WRITE (*, *) V1, V2, ............... ,Vn
This is also similar to the READ (*, *) V1, V2, ............... ,Vn.
The first asterisk indicates that the results are to be displayed on the screen. The second asterisk
indicates that the compiler will structure the output. The programmer has no control over how
the output is structured.
The first output column is reserved for a vertical control character which is always a blank with
list-directed output.
Integer numbers are right justified in a 13 column field width, i.e. the number will be placed as
far to the right in the field as possible, with any blanks in the field shown to the left of the
number. The 13-column field includes up to 10 digits, the algebraic sign (displayed only when
negative), and at least two leading blanks.
Examples:
WRITE (*,*) ADE, OLU
WRIRE (*,*) OJO
STOP AND END
STOP: The STOP statement is used to specify that the program execution is to be brought to a
halt. The form of the statement may be.
STOP
Or
STOP CONSTANT
Where constant is an integer constant with five or fewer digits, or a character constant. The use
of this word in FORTRAN 77 is optional
END: Every FORTRAN program and subprogram must conclude with an END statement that
indicates to the compiler that the end of the program unit has been reached. This statement is of
the form:
END
This must be the last statement of the program unit.
There are 3 major differences between these two keywords (END and STOP).
1. STOP is an instruction to the computer to stop the program, where the END statement is an
instruction to the compiler that there are no more statements in the program unit.
2. The STOP statement may be used anywhere in a program unit to stop execution and run
time. The END statement is used only as the physical end of a program unit.
3. The STOP statement may include a reference number, whereas the END statement does not
contain anything but the word END.
RELATIONAL EXPRESSION
A relational expression consists of two arithmetic expressions, or character strings, connected by
a relational operator that defines the nature of the condition, or relation to be tested.
Relational Operator in FORTRAN
Relational Operator Application in FORTRAN Meaning
.LT A. LT. D A is less than B
.LE A. LE. B A is less than, or equal to B
.EQ A. EQ. B A is equal to B
.NE A. NE.B A is not equal to B
.GT A. GT.B A is greater than B
.GE A. GE. B A is greater than, or equal to, B
The value of a relational expression is one of the logical values. TRUE or FALSE.
NUMBER COMPARISONS
The operators can be used to compare numerical values. The numerical order is used when two
numbers are compared.
For example
If X = 20.00 Y = 4.0 and M = 5.0
1. X + 5 .GT. M * Y
i.e. 25.0 .GT. 20.0 (The value is true)
2. X/Y .EQ. M
i.e. 20.0 / 4.0 = 5.0.
5.0 .EQ. 5.0 (The value is true)
3. 3 * (X + Y)/4 .LE. 2 * X + 5 * Y – 42.01
i.e. 18.0 . LE. 17.9 (The value is true)
CHARACTER COMPARISONS
We may use ASC11 (American Standard Code for Information Interchange) and EBCDIC
(Extended Binary Coded Decimal Interchange Code) Codes to obtain the collating sequences for
the characters for these codes. Thus, the relational expressions
‘B’ .GT. ’A’
‘X’ .LT. ‘Y’
are all. True. Since ‘B’ must follow ‘A’ and ‘X’ must precide ‘Y’
However,
‘A’ .GT. ‘1’
‘*’ .LT. ‘C’
depends on the collating sequences used in a particular computer. The first is true and second
false for ASCII but both are false for EBCDIC Code.
‘COMPUTER’ .GT. ‘COMPUTER’
Is true since a blank character (b) precedes all letters in every collating sequences
‘SHOLA’ .EQ. ‘SHOLA’ is true
GOTO STATEMENT (Unconditional)
Unconditional Transfer: The unconditional transfer of control can be accomplished by writing
the statement.
GOTO n
Where n is a statement number. This tells the computer to go, unconditionally, to the part of the
program beginning with the statement labeled.
Obviously, the statement labeled n must be executable.
The Computed GOTO Statement
The computed GOTO statement is a conditional transfer statement that transfers to one of several
executable statements, depending on the value of an integer numerical indicator. The general
form for the computed GOTO statement is:
GOTO (n¹, n2, n3,.... ¹ ) intexp
Where n¹, n2, n3,.... ¹ are the first, second, third etc., statement labels in a list of statements label
and intexp is an integer –variable or integer –arithmetic expression (the numerical indicator)
whose value determines to which of these labeled statements (first, second, third, etc) transfer
parenthesis is optional and may be omitted. If the value of intexp is less than one (zero or
negative integer) or greater than the number of statement labels in the list, the computed GOTO
statement is ignored and execution continues with the next executable statement following the
computed GOTO statement. Example.
GOTO (10, 25, 50, 35), K-J
Transfer is made to statement 10 if K – J = 1 ; to statement 25 if K- J = 2; to statement 50 if k – J
= 3; and to statement label 35, the value K- J = 4. Since these are four statement labels, the value
K – J must equal 1 through 4, inclusive, if the computed GOTO statement is to be executed, and
the values for K and J must have been assigned earlier in the program.
IF Statement
There are three forms of IF statements Logical IF, block IF, and Arithmetic IF. The blocks IF is
preferred except for simple selective structures, in which case the logical IF is used. The
arithmetic IF is error prone and hence, its use is discouraged.
Logical IF Statement
The logical IF statement makes possible the conditional execution of a single statement
depending upon whether a given logical expression is true. It has the form:
IF (Logical expression) statement where the statement is any executable FORTRAN statement,
but it cannot be another IF statement and END statement, or a DO statement.
When a logical IF statements is executed, the value of the logical expression is determined and if
it is true, the designated statement is executed (except when there is another transfer of control),
the statement following the logical IF statement is executed next. But if the expression returns
false, the designated statement is not executed, and the next statement to be executed is the one
following the Logical IF statement.
Examples:
IF (TOKS .LE. 105) PRINT *, TOKS
Toks is printed only if it is . 105.
IF (SALARY. LT. 3000.0 AND. STATUS .GT. 2.0) INC = INC + 1
Here, 1 is added to INC only if SALARY . 3000 and STATUS > 2.
IF (SCORE .GT. 90.0 .OR. GRADE .GE. 4.1) GOTO 99 Here, again, the program control is
transferred to the statement labeled 99, if SCORE > 90 or GRADE . 4.1
BLOCK IF STATEMENT (IF, THEN, ELSE, AND , END IF Statement)
The logical IF statement allows the programmer to control logic flow while minimizing the
under transfer steps. The general form is:
IF (Logical expression) THEN
. )
. )Statement set 1
. )
. )
ELSE
. )
. ) Statement set 2
. )
END IF
Basic Block IF structure.
In this structure, the logical expression in the IF THEN statement is identical to the form (s) used
logical IF statement. Statement set 1 and statement set 2 normally consist of one or more
statement to be executed. If the logical expression is true control is transferred to the first
statement in statement set 1 and the statement between the IF THEN statement and the ELSE
statements are executed. After the completion of the statements within statement, control is
transferred to the statement immediately following the END IF statement. The statements in
statement set 1 are ignored and control is transferred to the statement of statement set 2. When
completion of the execution of the statements within statement set 2 is accomplished, control is
transferred to the statement immediately following the END IF statement.
Example:
To calculate the square root of the difference between two numbers:
Solution
N= 0
10 READ (5, *) A, B
N = N + 1
IF (A – B.GE. 0.0) THEN
ROOT = (A – B) * * 0.5
WRITE (6,*) ‘THE REAL ROOT OF A – B IS’, ROOT
ELSE
ROOT = (B – A) * * 0.5
WRITE (6,*) ‘THE IMAGINARY SQUARE ROOT OF B – A IS’, ROOT
END IF
IF (N. NE.5) GOTO 10
STOP
END
8.5 REPETITIVE STRUCTURES.
This is also known as interactive structure or program loop. In a repetitive structure, a set of
program statements appears only once in the program. This results in a substantial reduction of
the number of statement consists of an entry point including initialization of certain variables, a
repetition, or loop, body, and an exit point.
The number of repetitions in a structure can be condition-controlled, or counter-controlled.
IF LOOP
The simplest of the repetitive structures is the If Loop in which the number of repetitions can be
conditional controlled, or counter-controlled. It involves the use of the IF and the GOTO
statements.
Example,
N = O
1OO READ *, A, B, SUM
SUM = A + B
PRINT *, A, B, SUM
N = N + 1
IF (N .LE. 10) GOTO 100
STOP
END
In the above program, N is used as a counter. In this case, it counts the number of interaction and
terminates it when it reaches 10.
DO LOOP
The explicit DO statement is an executable statement that causes a portion of the program to be
repeated a given number of times – a procedure called looping. The statements repeatedly
executed during the looping procedure are referred as the DO Loop. The DO loop is initiated
and controlled by an executable statement designated by statement label in the DO statement.
The general form is:
DO i j = k,m,n
Where i represents a statement label identifying the terminal statement (always an integer
constant)
j represents an integer-variable name called the index
k and m represent, respectively, the initial and limiting integer values to be assigned to the index
j
n represents the integer increment of the index (other than zero)
The index j is always an integer-variable name. The initial and limiting value k and m may be
integer constants integer-variable names, or integer-arithmetic expressions evaluated positive,
negative, or zero. The increment n may be an integer constant, an integer-variable name, or an
integer-arithmetic expression, evaluated positive or negative, but not zero.
It is essential that a programmer know how many times a loop will be repeated. The number of
increment is the difference between the limiting value m and the initial value k divided by the
increment n, truncated to integer form. Therefore,
NR = m – k + 1
n
where NR = number of repetitions (or iterations) of the
DO Statement
k = initial value specified in the DO statement
m = limiting value specified in the DO statement
n = increment specified in the DO statements.
Example,
DO 5O J = 1, 7, 2
Increment
Limiting Value
Initial Value
Index (integer variable)
Statement label defining range of loop.