Introduction-to-programming-using-Fortran-95.pdf

8/10/2019 Introduction-to-programming-using-Fortran-95.pdf

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Introduction to

Programmingusing

Fortran 95

Ed Jorgensen

June, 2013

Version 1.5


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Cover Diagram

The cover image is the plotted output from the chaos gameprogram from chapter 11. Theimage was plotted with !"plot.

Copyright

Ed Jorgensen 2013

#ou are free$ to %hare & to cop', distri(ute and transmit the wor)

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"nder the following conditions$ ttri(ution. #ou must attri(ute the wor) to -ntroduction to /rogramming using ortran

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!othing in this license impairs or restricts the author7s moral rights.

ii


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Table of Contents

1 Introduction....................................................................................................................................... 1

1.1 8h' 9earn /rogramming............................................................................................................ 1

1.2 ortran......................................................................................................................................... 1

1.3 :omplete ortran 5 ;ocumentation.......................................................................................... 11.< 8hat s /rogram...................................................................................................................... 2

1.5 =perating %'stem........................................................................................................................ 2

2 Computer Organization.................................................................................................................... 3

2.1 rchitecture =verview................................................................................................................ 3

2.2 :ompiler...................................................................................................................................... movies.

1. Fortran

ortran is a programming language often used (' the scientific communit'. ts name is a contraction of

=*mula T*!slation. =*T*! is one of the earliest programming languages.

This te+t utili@es the ortran 05 standard. =lder versions of ortran, li)e ortran BB, are notreferenced. The older ortran versions have less features and reAuire additional, often (urdensome

formatting reAuirements.

1.! Com"lete Fortran 95 #ocumentation

This te+t it is not a comprehensive or complete reference to the ortran 5 language. The entire !"

ortran compiler documentation is availa(le on6line at the following location$

http://gcc.gnu.org/onlinedocs/gcc-4.5.0/gfortran/

f this location changes, a we( search will (e a(le to find the new location.

1


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:hapter 1 K ntroduction

1.$ What Is % Program

computer programis a series of instructions which ena(les the computer to perform a designated

tas). s this te+t will demonstrate, a computer must (e told what to do in precise, step6('6step detail.These steps might include o(taining data, arithmetic operations additional, su(traction, multiplication,

division, etc.4, data storage, and information output. The computer will perform these tas)s as

instructed, even if the' don7t alwa's ma)e sense. :onseAuentl', it is the programmer who mustdevelop a solution to the pro(lem.

1.5 &"erating 'ystem

The =perating %'stem, or =%, is an interface (etween the user and the hardware :/", memor',screen, dis) drive, etc.4. The =% is responsi(le for the management of the hardware, coordination of

activities and the sharing of the resources of the computer that acts as a host for computing applications

run on the machine. The common operating s'stems include various versions of 8indows. I: =%

, and "!9inu+. /rograms written in ortran will wor) on these operating s'stems.

2


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Com"uter &rgani(ation

>efore writing programs, it is useful to understand some (asics a(out how a computer is organi@ed.

This section provides a (rief, high6level overview of the (asic components of a computer and how it is

organi@ed.

.1 %rchitecture &)er)ie*

The (asic components of a computer include a :entral /rocessing "nit :/"4, *andom ccess

Iemor' *I4, ;is) ;rive, and nput=utput devices i.e., screen and )e'(oard4, and aninterconnection referred to as >"%.

ver' (asic diagram of a computer architecture is as follows$

/rograms and data are t'picall' stored on the dis) drive. 8hen a program is e+ecuted, it must (e

copied from the dis) drive into the *I memor'. The :/" e+ecutes the program from *I. This issimilar to storing a term paper on the dis) drive, and when writingediting the term paper, it is copied

from the dis) drive into memor'. 8hen done, the updated version is stored (ac) to the dis) drive.

3

Illustration 1: Computer Architecture

Screen / Keyboard /

Mouse

Disk Drive /

Other Storage Media

Random Access

Memory (RAM)CP

!S

("nterconnection)


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:hapter 2 K :omputer =rgani@ation

. Com"iler

/rograms are written in the ortran programming language. However, the :/" does not read ortran

directl'. nstead, the ortran program that we create will (e converted into (inar' 17s and 07s4 (' thecompiler. The :/" will read the instructions and information, represented in (inar', and perform the

commands from the program.

The compiler is a program itself and is reAuired in order to create the files needed to e+ecute programs

written in ortran 5.

.! Information +e"resentation

ll information, including num(ers, characters, and instructions are represented in the computer in

(inar' 17s and 07s4. The information is converted into (inar' representation 17s and 07s4 for storage in

the computer. ortunatel', this is generall' done transparentl'.

2.3.1 Decimal Numbers

>efore discussing (inar' num(ers, a (rief review of the decimal s'stem is presented. The num(erL123


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:hapter 2 M :omputer =rgani@ation

2.3.2 Binary Numbers

The (inar' s'stem, as well as its math, operates in base 2, using two s'm(ols, 0 and 1.

2B 2 25 2< 23 22 21 20

12C < 32 1 C < 2 1

0 0 0 0 1 1 0 1

n (ase 2, we put the digits 061 in columns 20, 21, 23, and so on. or e+ample,

11012 = 123 12

2 02

1 12

0= Celow are some Aui@ Auestions (ased on this chapter.

2.4.1 Quiz Questions

>elow are some Aui@ Auestions.

14 How is information represented in the computerN

24 8hat does the ortran compilerdoN

34 8hat architecture component connects the memor' to the :/"N


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:hapter 2 K :omputer =rgani@ation


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! -etting 'tarted

This section provides a (rief overview of how to get started. This includes the general process for

creating a ver' simple program, compiling, and e+ecuting the program. %ome detailed steps regarding

wor)ing with files, o(taining the compiler, and compiling a program are included inAppendix B!indo"s #tart$up Instructions.

!.1 +euired '/ills

>efore starting, 'ou should have some (asic computer s)ills, including the following$

(ilit' to use a we( (rowser

>asic understanding of computer director' structure ile manipulation create, delete, rename, move, etc.4 (ilit' to edit a te+t file

ncludes selecting and learning a te+t editor i.e., !otepad, !otepadOO, emacs, etc.4

f 'ou are unsure a(out an' or all of these reAuirements 'ou will need to learn them. ortunatel', the'

are not difficult. dditionall', there are numerous tutorials availa(le on the 8e(.

The following sections assume the the ortran 5 compiler is installed and availa(le. or additional

information regarding o(taining and installing the compiler, refer to ppendi+ >. The ortran 5

compiler is availa(le for download at no cost.

!. Program Formats

ortran 5 programs must (e written and formatted in a specific manner. The following sections

summari@e the (asic program elements followed (' a simple e+ample.

3.2.1 Program tatement

ortran 5 program is started with a program statement, 7program 7, and ended with an end

program statement, 7end program 7. *efer to the e+ample first program to see an e+ample of

these statements.

3.2.2 Comments

:omments are information for the programmer and are not read (' the computer. or e+ample,

comments t'picall' include information a(out the program. or programming assignments, the

comments should include the programmer name, assignment num(er, and a (rief description of theprogram.

B


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:hapter 3 K etting %tarted

3.2.3 imple !utput

program can displa' a simple message to the screen (' using the "ritestatement. or e+ample$

write(*,*) "Hello World"

8ill displa' the message Hello World to the screen. dditional information regarding the write

statement and outputting information is provided in later chapters.

3.2.4 "#ample $ %irst Program

The following trivial program illustrates the initial formatting reAuirements.

! Simple Example Programprogram first

write (*,*) "Hello World"

end program first

n this e+ample, the program is named 7first7. This file is t'picall' referred to as thesourcefile.

!.! Text ,ditor

The first step is to create a te+t file named hw.f95 using a te+t editor. t is useful to place programsand various files into a wor)ing director'. This wa' the files can (e easil' found and not confused with

other, unrelated files and data. The hw.f95 file should (e created and placed in the wor)ingdirector'.

file name is t'picall' comprised of two partsP a name and an e+tension. n this e+ample, the name ishw and the e+tension is .f95. The usual e+tension for this a future programs will (e .f95whichindicates that the file is a ortran 5 source file.

The following e+amples will use the hw.f95 file name. f desired, a different file name ma' (eused. However, the name will need to (e adFusted for the compiler and e+ecute steps.

!.$ Com"iling

=nce the program is t'ped into a file, the file must (e compiled. :ompiling will convert the human

reada(le ortran program, or source file, into a computer reada(le version in (inar'4.

n the e+amples (elow, the commands t'ped (' the user are displa'ed in (old. The regular non6

(olded4 te+t refers to prompts or other information displa'ed (' the computer which will not need to(e t'ped4.

To compile the e+ample program, the following command would (e entered$

K:\mydir>gfortran -o hw hw.f95

This command will tell the 7gfortran7 compiler to read the file hw.f95and, if there are no errors,

C


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:hapter 3 M etting %tarted

create an e+ecuta(le file named hw.exe. f there is an error, the compiler will generate an errormessage, sometimes cr'ptic, and provide a line num(er. %uch errors are usuall' the result of mist'ping

one of the instructions. n' errors must (e resolve (efore continuing.

!.5 ,xecuting

To e+ecute or run a program, t'pe the name of the e+ecuta(le file. or e+ample, to e+ecute or run the

hw.exeprogram$

K:\mydir>hwHello World

K:\mydir>

8hich will e+ecute the e+ample program and displa' the -Hello 8orld message to the screen. more

complete e+ample is as follows$

t is not necessar' to t'pe the e+tension i.e., -.e+e4 portion of the file name.

!.0 ,xercises

>elow are some Aui@ Auestions and proFect suggestions (ased on this chapter.

3.&.1 Quiz Questions


14 8hat the the input file for the compilerN

24 8hat is the output file from the compilerN

34 ortran program must start with and end with what statementN


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:hapter 3 K etting %tarted


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$ Fortran 95 2asic ,lements

>efore (eginning to writing programs, it is necessar' to )now some of the (asic elements of the

ortran language. This section descri(es some of the (asic elements of ortran. dditionalinformation will (e added in later sections.

$.1 3ariables

The (asic concept in a program is the concept of a varia(le. Varia(les in a program are li)e varia(les inan alge(raic e+pression. The' are used to hold values and then write mathematical e+pressions using

them. ortran allows us to have varia(les of different t'pes.

varia(le can hold one value at a time. f another value is placed in the varia(le, the previous value is

over6written and lost.

Varia(le !ame Q


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:hapter < K ortran 5 D >asic Elements

4.1.2 *ey+or's

n programming, a )e'word is a word or identifier that has a special ortran meaning. or e+ample, in

the -hello world program from the previous chapter, the wordprogramhad a special meaning in that itused to note the start or (eginning of a program. dditionall', the word "ritehas a special meaning to

note an output action e.g., writing some information to an output device, li)e the screen4.

%uch )e'words are reserved in that the' can not (e used for an'thing else such varia(le names. That is,

a varia(le name of program or write is not allowed.

s additional ortran 5 statements and language constructs are e+plained, more )e'words willidentified. n general, words used for ortran language statements, attri(utes, and constructs will li)el'

(e )e'words. complete list of )e'words or reserved words is located in ppendi+ .

$. #ata Ty"es

ortran, li)e man' other high level programming languages, supports several different data t%pesto

ma)e data manipulation easier. The most freAuentl' used data t'pes are integer and floating point.

=ther data t'pes are comple+ num(ers, characters and logical data.

n a ortran statement, data can appear either as a literal e.g., an actual value such as 3.1


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:hapter < M ortran 5 D >asic Elements

4.2.2 Real

real num(er2includes the fractional part, even if the fractional part is 0. *eal num(ers, also referred

to as floating point num(ers, include (oth rational num(ers and irrational num(ers. E+amples of

irrational num(ers or repeating decimals include , 2 and e. dditional e+amples include 1.5, 5.0,and 3.1


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4.3.1 Declaring )ariables

;eclaring varia(les formall' defines the data t'pe of each varia(le and sets aside a memor' location.

This is performed (' a t'pe declaration statement in the form of$

::

The t'pe must (e one of the predefined data t'pes integer, real, comple+, character, logical4. =utlined

in the previous section. ;eclarations are placed in the (eginning of the program after the programstatement4.

or e+ample, to define an integer varia(le toda%,

integer :: today

dditional e+amples include$

integer :: today, tomorrow, yesterdayreal :: ans2

complex :: zlogical :: answer

The declarations can (e entered in an' order.

dditional information regarding character varia(les is provided in a later chapter.

4.3.2 ,nitialization

t is possi(le to declare a varia(le and to set it is initial value at the same time. This initiali@ation is not

reAuired, (ut can sometime (e convenient. or e+ample, to define an integer varia(le toda%sdateand

set it to the 15thof the month$

integer :: todaysdate=15


integer :: todaysday=15, tomorrow=16, yesterday=14real :: ave = 5.5

%paces or no spaces (etween the varia(les, eAual signs, semicolons, and commas are allowed.

Varia(les initiali@ed at declaration can (e changed later in the program as needed.

4.3.3 Constants

constantis a varia(le that can not (e changed during program e+ecution. or e+ample, a programmight declare a varia(le for ;and set it to 3.1


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:hapter < M ortran 5 D >asic Elements

or e+ample, the declarations$

real, parameter :: pi = 3.14159integer, parameter :: width = 1280

will set the varia(lepito 3.1


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$.0 ,xercises


4.&.1 Quiz Questions


14 8hat are the five ortran 5 data t'pesN

24 8hat should a ortran varia(le name start withN

34 8hat data t'pe are each of the following num(ers integer or real4N


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5 ,x"ressions

This section descri(es how to form (asic ortran 5 e+pressions and perform arithmetic operations

i.e., add, su(tract, multiple, divide, etc.4. E+pressions are formed using literals actual values4,

varia(les, and operators i.e.,


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:hapter 5 K E+pressions

The following are some real constants using e6notation$

2.75E63.3333E-1

Hence, 2.B5E5 is 2.B5105 or 2B5,000 and 3.333E61 is 3.333101 or 0.3333 or appro+imatel'

one third.

-.1.3 Comple# iterals

complexconstantis designated (' a pair of constants integer or real4, separated (' a comma and

enclosed in parentheses. E+amples are$

(3.2, -4.1)(1.0, 9.9E-1)

The first num(er denotes the real part and the second the imaginar' part. 8hile a comple+ num(er

consits of two elements it is considered a single value.

-.1.4 Character iterals

characterconstantis either a single character or a set of characters, called a string. character is a

single character enclosed in Auotes. string consists of an ar(itrar' seAuence of characters also

enclosed in Auotes. %ome e+amples include$

"X""Hello World""Good bye cruel world!""Have a nice day"

:haracter and string constants enclosed with Auotes4 are case sensitive. %o, character - upper6

case4 is not the same as -+ lower6case4.

pro(lem arises if 'ou want to have a Auote in the string itself. dou(le Auote will (e interpreted as a

single within a string.

"He said ""wow"" when he heard"

The dou(le6Auoting is sometimes referred to as an escape character. %trings and characters must (eassociated with the character data t'pe.

-.1.- ogical Constants

The fifth t'pe is logicalconstant. These can onl' have one of two values$.true..false.

The dots enclosing the true and false are reAuired.

1C


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:hapter 5 M E+pressions

5. %rithmetic &"erations

This section summari@es the (asic arithmetic operations.

-.2.1 ssignment

ssignment is term for setting a varia(le eAual to some value. ssignment is performed with a eAual>4 sign. The general form is$

variable = expression

The e+pression ma' (e a literal, varia(le, an arithmetic formula, or com(ination of each. =nl' oneassignment to a single varia(le can (e made per line.

or e+ample, to declare the varia(le ans"er1as a real value,

real :: answer1

and set it eAual to 2.B1C2C1C3,

answer1 = 2.71828183

The value for ans"er1can (e changed as often as needed. However, it can onl' hold one value at a

time.

-.2.2 ''ition

The ortran addition operation is specified with a plus sign O4. or e+ample, to declare the varia(les,

sum, number1, number2, and number&,

integer :: sum, number1=4, number2=5, number3=3

and calculate the sum,sum = number1 + number2

which will set the varia(le sum to in this e+ample. The data t'pes of the varia(les, integer in thise+ample, should (e the same. Iultiple varia(les can (e added on one line. The line can also include

literal values. or e+ample,

sum = number1 + number2 + number3 + 2

which will set the varia(lesumvaria(le to 1


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should (e the same. Iultiple varia(les can (e su(tracted on one line. The line can also include literal

values. or e+ample,

ans = value1 - value2 value3

which will set the varia(le ansvaria(le to 1.0. dditionall', it will over6write the previous value of 2.0.

-.2.4 ultiplication

The ortran multiplication operation is specified with an asteris) Y4. or e+ample, to declare thevaria(les, ans, 'alue1, 'alue2, and 'alue&,

real :: ans, value1=4.5, value2=2.0, value3=1.5

and calculate the product,

ans = value1 * value2

which will set the varia(le ansto .0. The data t'pes of the varia(les, real in this e+ample, should (e

the same. Iultiple varia(les can (e multiplied on one line. The line can also include literal values.or e+ample,

ans = value1 * value2 * 2.0 * value3

which will set the varia(lesumto 2B.0. dditionall', it will over6write the previous value of .0.

-.2.- Diision

The ortran division operation is specified with a slash s'm(ol 4. or e+ample, to declare thevaria(les, ans, 'alue1, 'alue2, and 'alue&,

real :: ans, value1=10.0, value2=2.5, value3=2.0

and calculate the Auotient,

ans = value1 / value2

which will set the varia(le ansto


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and calculate the e+ponentiation,

ans = value1 ** 3

which will set the varia(le ansto C.0. The data t'pes of the varia(les, real in this e+ample, should (ethe same.

5.! Precedence of &"erations

ortran follows the standard mathematical precedence of operations. That is multiplication anddivision are performed (efore addition and su(traction. urther, in accordance with mathematical

standards, the e+ponentiation operation is performed (efore multiplication and division.

The following ta(le provides a partial summar' of the (asic ortran 5 precedence levels$

)recedence

+eve&

Operator Operation

1st unar' 6

2nd == e+ponentiation

3rd = - multiplication and division


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or e+ample, the cosine of ;is 61. n ortran, to declare the varia(lesxandpi,

real :: zreal, parameter :: pi = 3.14159

and then calculate the cosine of the varia(lepi,

z = cos(pi)

which will setzto 61.0. The varia(lepiis the input argument and the result returned is assigned to the

varia(lez.

-.4.2 Conersion %unctions

=ther intrinsic functions include functions to change the t'pe of varia(les or values. The (asic

conversion functions are as follows$

Function %'p&anation

realZinteger argument[4 :onvert the Zinteger argument[ to a realvalue

intZreal argument[4 :onvert the Zreal argument[ to an integer,

truncates the fractional portion

nintZreal argument[4 :onvert the Zreal argument[ to an integer,

rounds the fractional portion

or e+ample, given the following varia(le declarations,

integer :: inum1=10, inum2, inum3real :: rnum1, rnum2 = 4.8

and calculate the ans1and ans2,

rnum1 = real(inum1)inum2 = int(rnum2)inum3 = int(rnum3)

which will set to rnum1to 10.0, inum2to


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!!T4 *eturns the nearest integer to real value thus rounding

up or down as appropriate4.

*E94 :onverts integer argument to real.

%!84 *eturns real sine of real argument 8 in radians.

%?*T84 *eturns the real sAuare root of real argument 8P 8 must (epositive.

T!4 *eturns the real tangent of real argument in radians.

more complete list of intrinsic functions in located in ppendi+ >.

5.5 4ixed 4ode

n general, mathematical operations should (e performed on varia(les of the same t'pe. 8hen (oth

integer and real values or varia(les are used in the same statement, it is called mi+ed mode.

*eal and integer operations$

1/2 = 01.0 + 1/4 = 1.01.0 + 1.0/4 = 1.25

when mi+6mode is encountered, integer is converted to real onl' when mi+ed6mode is encountered onthe same operation t'pe. :onversion ma' also occur on assignment.

"ne+pected conversions can cause pro(lems when calculating values. n order to avoid such pro(lems,

it is strongl' recommended to not use mi+6mode. There are a series of rules associated with mi+ed6

mode operations. or simplicit', those rules are not covered in here.

f it is necessar' to perform calculations with different data t'pes, li)e integers and reals, the

conversion functions should (e used correct and predicta(le results.

5.0 ,xam"les

>elow is an e+ample program that calculates velocit' (ased on acceleration and time. The programdeclares the appropriate varia(les and calculate the velocit'.

program velocity! Program to calculate the velocity from the! acceleration and time

! Declare variablesimplicit nonereal :: velocity, acceleration = 128.0real :: time = 8.0

! Display initial headerwrite (*,*) "Velocity Calculation Program"write (*,*)

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! Calculate the velocityvelocity = acceleration * time

write (*,*) "Velocity = ", velocity

end program velocity

dditional information regarding how to perform input and output in the ne+t chapter. The commentsare not reAuired, (ut help ma)e the program easier to read and understand.

5. ,xercises

>elow are some Aui@ Auestions and proFect suggestion (ased on this chapter.

-.5.1 Quiz Questions


14 8hat is assignmentoperatorN

24 8hat is the e+ponentiation operatorN

34 How can an integer varia(le (e converted to a real valueN


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-.5.2 uggeste' Pro(ects

>elow are some suggested proFects.

14 T'pe in the velocit' program, compile, and e+ecute the program. :hange the declared values,

compile, and e+ecute the modified program. Verif' the results of (oth e+ecutions with a

calculator.

24 8rite a program to calculate and displa' the difference (etween time as read from a sundial anda cloc). The difference can (e calculated with the -eAuation of time which is$

b 2(n *1) / 3(4

e .*7 $in(20) 7.!3 co$(b) 1.! $in(b)

8here, nis the da' num(er. or e+ample, nU 1 for Januar' 1, nU 2 for Januar' 2, and so on.

The program should read the value for n163


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0 'im"le In"ut and &ut"ut

%imple, unstructured, input and output can (e performed with the "riteand readstatements as

e+plained in the following sections. n a later chapter, a more structured approach will (e presented inlater sections.

0.1 &ut"ut Write

s noted from the first program, simple output can (e performed (' using the a "ritestatement. ore+ample$

write (*,*) "Hello World"

8hich will send the message, referred to as astring, ?e&&o or&dto the screen. The first -Y meansthe default output device, which is the screen or monitor. The second -Y refers to the 7free format7.Thus, the -(*,*) means to send it to the screen in 7free format7.

The free format allows the ortran compiler to determine the appropriate format for the information

(eing displa'ed. This is eas', especiall' when first getting started, (ut does not allow the program

much control over how the output will (e formatted or displa'ed on the screen.

dditionall', the value held (' declared varia(les can (e displa'ed. or e+ample, to declare the

varia(les num1, num2, and num&.

integer :: num1=20, num2=50, num3=10

the write statement to displa' num1would (e,write (*,*) num1

The free format allows the ortran compiler to determine the appropriate output format for the

information (eing displa'ed.

write statement with no string or varia(les,

write (*,*) num1

8ill displa' a (lan) line.

Iultiple varia(les and strings can (e displa'ed with one write statement. or e+ample, using the

previous declarations,write (*,*) "Number 1 = ", num1, "Number 2 = ", num2

The information inside the Auotes is displa'ed as is, including capitali@ation and an' spelling errors.8hen the Auotes are not used, it is interpreted as a varia(le. f the varia(le is not declared, a compiler

error will (e generated. The value assigned to each varia(le will (e displa'ed. value must have (e

assigned to the varia(le prior to attempting to displa'.

2B


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:hapter K %imple nput and =utput

&.1.1 !utput $ Print

n addition to the write statement, a print statement can (e used. The print statement will send output

onl' to the screen. Thus it is a more restrictive form of the write statement.

s with the write statement, multiple varia(les and strings can (e displa'ed with one print statement.

or e+ample, using the previous declarations,print *,"Number 1 = ", num1, "Number 2 = ", num2

The information inside the Auotes is displa'ed as is, including capitali@ation and an' spelling errors.

8hen the Auotes are not used, it is interpreted as a varia(le. f the varia(le is not declared, an error will(e generated. f the varia(le is defined, the value assigned to that varia(le will (e displa'ed.

n general, all e+amples will use the write statement.

0. In"ut +ead

To o(tain information from the user, a readstatement is used. or e+ample, to declare the varia(les

num1, num2,

integer :: ans1, ans2

then read a value for ans1from the user,

read (*,*) ans1

8hich will read a num(er from the user entered on the )e'(oard into the varia(le ans1. The Y,Y4means to send it to read the information in 7free format7. The free format allows the ortran compiler to

determine the appropriate format for the information (eing read.

Iultiple varia(les can (e read with one write statement. or e+ample, using the previous declarations,

read (*,*) ans1, ans2

will read two values from the user into the varia(les ans1and ans2.

%ince the read is using free format, two num(ers will (e reAuired. The num(ers can (e entered on the

same line with one more more spaces (etween them or on separate lines. The read will wait until two

num(ers are entered.

8hen reading information from the user, it is usuall' necessar' to provide a prompt in order to ensurethat the user understands that input is (eing reAuested (' the program. suita(le write statement with

an appropriate string, followed (' a read statement will ensure that the user is notified that input is

(eing reAuested.

or e+ample, to read a date, a program might reAuest month, date, and 'ear as three separate varia(les.iven the following declarations,

integer :: month, date, year

the program might prompt for and read the data in the following manner,

write (*,*) "Enter date (month, date, and year)"read (*,*) month, date, year

2C


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:hapter M %imple nput and =utput

%ince the program is reAuesting three integers, three integers must (e entered (efore the program

continues. The three num(ers ma' (e entered on one line with a single space (etween them, with

multiple spaces or ta( (etween them, or even on three different lines as in the following e+amples$

Enter date (month, date, and year)

10 17 2009

Enter date (month, date, and year)10172009

Enter date (month, date, and year)10 17 2009

The t'pe of num(er reAuested here is an integer, so integers should (e entered. /roviding a real

num(er or character i.e., letter4 would generate an error. 9ater chapters will address how to deal with

such errors.

0.! ,xam"le

>elow is an e+ample program that calculates the area of a circle. The program will declare the

appropriate varia(les, read the radius, calculate the circle area, and displa' the result.

Program circle! Program to calculate the area of a circle

! Declare variablesimplicit none

real :: radius, areareal, parameter :: pi = 3.14159

! Display initial header and blank linewrite (*,*) "Circle Area Calculation Program"write (*,*)

! Prompt for and read the radiuswrite (*,*) "Enter Circle Radius"read (*,*) radius

! Calculate the circle areaarea = pi * radius**2

! Display resultwrite (*,*) "Circle Area: ", area

end program circle

The comments are not reAuired, (ut help ma)e the program easier to read and understand. f the

program does not wor) at first, the comments can aid in determining the pro(lem.

2


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0.$ ,xercises


&.4.1 Quiz Questions


14 8hat does the(*,*) meanN

24 8hat is the statement to output a message -/rogramming is un\

34 8hat are the statements to declare and read the value for a persons age in 'ears.

&.4.2 uggeste' Pro(ects


14 T'pe in the circle area program, compile and e+ecute the program. Test the program on severalsets of input.

24 Iodif' the circle area program to reAuest a circle diameter. The formula for circler area must(e adFusted accordingl'. *ecall that radius U diameter divided (' two. Test the program on

several sets of input.

34 T'pe in the velocit' program from the previous chapter and update to prompt for and reAuestinput for the acceleration and time, and then displa' the results. Test the program on several

sets of input.


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:hapter M %imple nput and =utput

54 8rite a ortran program compute geometric information for a Gite. The program should read

the a,candplengths and compute the qlength. The program should

displa' an appropriate prompt, read the values, compute the answer, anddispla' the original input and the final result.

*ecall that$

q (a2

p2

4) ( c

2

p2

4)

Test the program on several sets of input.

31

a

pA

c


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32


43/179

Program #e)elo"ment

8riting or developing programs is easier when following a clear methodolog'. The main steps in the

methodolog' are$

"nderstand the /ro(lem :reate the lgorithm

;evelop the /rogram Test;e(ug the /rogram

To help demonstrate this process in detail, these steps will (e applied to a simple pro(lem to calculate

and displa' the period of a pendulum.

s additional e+amples are presented in later chapters, the' will (e e+plained and presented using thismethodolog'.

.1 6nderstand the Problem

>efore attempting to create a solution, it is important to understand the pro(lem. Ensuring a completeunderstanding of the pro(lem can help reduce errors. The first step is to understand the what is

reAuired and the applica(le input information. n this e+ample, the formula for the period of a

pendulum is$

Period 2

L

g

1+

1

4$in

2

2

8here$

g U C0 cmsec2

U 3.1othggravit'4 and should (e declared as a constants. The formula is a simplified version of the

more general case. s such, for ver' large, ver' small, or @ero angle values the formula will not

provide accurate results. or this e+ample, that is accepta(le.

s shown, the pendulum is attached to a fi+ed point, and set into motion (' displacing the pendulum(' an angle, , as shown in the diagram. The program must define the constants forgand , declare

the varia(les, displa' appropriate prompts, read the values forLand then calculate and displa' the

original input and the period of the pendulum with the given length and angle of displacement.

33

9

]


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:hapter B K /rogram ;evelopment

. Create the %lgorithm

The algorithm is the name for the ordered seAuence of steps involved in solving the pro(lem. =nce the

program is understood, a series of steps can (e developed to solve that pro(lem. There can (e multiplecorrect solutions to a given pro(lem.

The process for creating an algorithm can (e different for different people. n general, some timeshould (e devoted to thin)ing a(out a possi(le solution. This ma' involve wor)ing on some possi(le

solution on a scratch piece of paper. =nce a possi(le solution is selected, that solution can (edeveloped into an algorithm. The algorithm can (e written down, reviewed, and refined. This

algorithm is the outline of the program.

or this pro(lem, the varia(les and constants must (e declared, the applica(le headers and prompts

displa'ed, and the values forLand read from the user. Then the period can (e calculated (ased onthe provided formula and the results displa'ed. ormali@ing this, the following steps can (e developed

and written down as follows$

! declare variables

! real constants -> gravity, pi! reals -> angle, length! display initial header! prompt for and read the length and angle values! calculate the period! display the results

8hile this is a fairl' straightforward algorithm, more comple+ pro(lems would reAuire more e+tensive

algorithms. E+amples in later chapters will include more comple+ programs. or convenience, the

steps are written a program comments. This will allow the addition of the code to the (asic algorithm.

.! #e)elo" the Program>ased on the algorithm, the following program can (e created.

program period! Program to calculate the period of a pendulum

! declare variables! real constants -> gravity, pi! reals -> angle, lengthimplicit nonereal :: angle, length, pperiodreal, parameter :: gravity=980.0, pi=3.14159

! display initial headerwrite (*,*) "Pendulum Period Calculation Program"write (*,*)

! prompt for and read the length and angle valueswrite (*,*) "Enter Length and Angle values:"read (*,*) length, angle

3


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:hapter B M /rogram ;evelopment

! calculate the periodpperiod = 2.0 * pi * sqrt(length/gravity) * &

( 1.0 + 1.0/4.0 * sin(angle/2.0)**2 )

! display the resultswrite(*,*) "The period is:", pperiod

end program period

The indentation is not reAuired, (ut helps ma)e the program easier to read. !ote that the -2, -1, and

-


46/179


n this case, the compiler error displa'ed will appear as follows$

c:\mydir> gfortran -o period period.f95period.f95:13.1:

wrote (*,*)1Error: Unclassifiable statement at (1)

The first digit, 13 in this e+ample, represents the line num(er where the error occurred. "sing a te+teditor that displa's line num(ers, the statement that caused the error can (e Auic)l' found and

corrected.

f the declaration for the varia(le lengthis omitted, the error would appear as follows$

c:\mydir> gfortran -o period period.f95period.f95:17.18:

read (*,*) length, angle 1Error: Symbol 'length' at (1) has no IMPLICIT type

n this case, the error is shown on line 1C first digit after the -$4. However, the actual error is that thevaria(le length is not declared. Each error should (e reviewed and evaluated.

5.4.1.2 Runtime "rror

run6time error is something that causes the program to crash. or e+ample, if the a num(er isreAuested from the user and a letter is entered, that can cause occur.

or e+ample, the period program e+pects two real num(ers to (e entered. f the user enters letters, +and ', in this e+ample, an error will (e generated during the e+ecution of the program as follows$

c:\mydir> periodPendulum Period Calculation Program

Enter Length and Angle values:x y

At line 17 of file period.f95 (unit = 5, file = 'stdin')Fortran runtime error: Bad real number in item 1 of list input

The program was e+pecting numeric values and letters were provided. %ince letters are not meaningful

in this conte+t, it is an error and the program -crashes or stops with an error message.

9ater chapters will provide additional information on how to deal with such errors. "ntil then, provingthe correct data t'pe will avoid this )ind of error.

3


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:hapter B M /rogram ;evelopment

5.4.1.3 ogic "rror

logic error is when the program e+ecutes, (ut does not produce the correct result. or e+ample,

coding a provided formula incorrectl' or attempting to computer the average of a series of num(ers

(efore calculating the sum.

or e+ample, the correct formula for the period of a pendulum is as follows$pperiod = 2.0 * pi * sqrt(length/gravity) * &

( 1.0 + 1.0/4.0 * sin(angle/2.0)**2 )

f the formula is t'ped incorrectl' or incompletel' as follows$

pperiod = 2.0 * pi * sqrt(length/gravity) * &( 1.0 + 1/4 * sin(angle/2.0)**2 )

The 1 over < is entered as -1


48/179


5.-.2 uggeste' Pro(ects


14 T'pe in the pendulum period calculation program, compile, and e+ecute the program. Test the

program using several different input values.

24 :reate a program to prompt for and read the circle area from the user and calculate the

circumference of a circle using the following formula$

circumference 2

Circlerea

Test the program using several different input values.

34 :reate a program to prompt for and read the radius of a sphere from the user and calculate thesurface area of the sphere using the following formula$

sphere!urface rea

4 r2

Test the program using several different input values.


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8 'election 'tatements

8hen writing a program, it ma' (e necessar' to ta)e some action (ased on the outcome of comparing

the values of some varia(les. ll programming languages have some facilit' for decision6ma)ing.That is, doing one thing if some condition is true and optionall'4 doing something else if it is not.

ortran statements andor :%E statements are used to allow a program ma)es decisions.

8.1 +elational ,x"ressions

The first step is to compare two values, often contained in varia(les. The wa' two values are comparedis with relational operators. The varia(les are often referred to as operands. *elational operators are

used (etween varia(les or operands of similar t'pes. That is real to real, integer to integer, logical to

logical, and characterstring to characterstring.The (asic relational operators are$

6e&ationa&

Operation

6e&ationa& Operator

@norma&A

6e&ationa& Operator

@a&ternateA

reater than B .gt.

reater than or

eAual

B> .ge.

9ess than .&t.

9ess than or eAual > .&e.

EAual to >> .e.

!ot eAual to -> .ne.

The normal form will (e used for e+amples in this te+t. However, the alternate form ma' (e used at

an' time. The alternate forms are used to support older ortran programs.

relational operation is used to form a relational e+pression. The result of a relational e+pression must

alwa's result in either a trueor(alseresult.

The ->> two eAual signs4 is used to compare. The -> single eAual4 is used for assignment settinga varia(le4. The ->> does not change an' values, while the -> does.

or e+ample, given the declaration of,

integer :: gamelives

it might (e useful to )now if the current value of gamelivesis greater than 0.

3


50/179

:hapter C K %election %tatements

n this case, the relational e+pression would (e,

(gamelives == 0)

8hich will result in a trueor(alseresult (ased on the value of -gamelives.

8. Logical &"erators

9ogical operators are used (etween two logical varia(les or two logical e+pressions. The' are$

+ogica& Operator %'p&anation

.and. the result is true if bothoperands are true

.or. the result is true if eitheroperand is true

.not. logical negate if true, ma)es false and if

false, ma)es true4

9ogical operators are used to com(ine relational operations as needed.


integer :: gamelives, extralives

it might (e useful to )now if the current value of gamelivesis greater than 0. n this case, the

relational operation would (e,

( (gamelives == 0) .and. (extralives == 0) )

which will result in a trueor(alseresult. %ince the !; logical operation is used, the final result will

(e trueonl' if (oth logical e+pressions are true.

nother wa' of chec) the status might (e,

( (gamelives > 0) .or. (extralives > 0) )

which still results in a trueor(alseresult. However, since the orlogical operation is used, the final

result will (e trueif either logical e+pressions is true.

The relational operators have higher precedence than logical operators.

8.! IF 'tatements

statements are used to perform different computations or actions (ased on the result of a logicale+pression which evaluates to true or false4. There are a series of different forms of the (asic statement. Each of the forms is e+plained in the following sections.


51/179

:hapter C M %election %tatements

6.3.1 ,% 0/"N tatement

The statement, using the relational operators, is how programs ma)e decisions. The general format

for an statement is as follows$

if ( ) then

end if

8here the Zfortran statements[ ma' include one or more valid ortran statements.



(ased on the current value of gamelivesis, a reasona(le statement might (e$

if ( gamelives == 0 ) thenwrite (*,*) "Game Over."write (*,*) "Please try again."

end if

8hich will displa' the message -ame =ver if the value of gamelivesis less than or eAual to 0.

6.3.1.1 ,% 0/"N tatement7 imple %orm

dditionall', another form of the statement includes

if ( )

n this form, a single statement is e+ecuted if the relational e+pression evaluates to true. The previouse+ample might (e written as

if ( gamelives == 0 ) write (*,*) "Game Over."

n this form, no -then or -end if are reAuired. However, onl' one statement can (e e+ecuted.

6.3.2 ,% 0/"N "" tatement

The THE! E9%E statement e+pands the (asic statement to also allow a series of statements to (e

performed if the logical e+pression evaluates to(alse.

The general format for an THE! E9%E statement is as follows$

if ( ) then

else

end if



52/179




(ased on the current value of gamelivesis, a reasona(le THE! E9%E statement might (e$

if ( gamelives > 0 ) thenwrite (*,*) "Still Alive, Keep Going!"

elsewrite (*,*) "Extra Life Granted."gameslives = 1

end if

8hich will displa' the message -%till live, Geep oing if the value of gamelivesis greater than 0

and displa' the message -E+tra 9ife ranted if the value of gamelivesis less than 0.

6.3.3 ,% 0/"N "" ,% tatement

The THE! E9%E statement e+pands the (asic statement to also allow a series of statementsto (e performed in a series.

The general format for an THE! E9%E statement is as follows$

if ( ) then

else if ( ) then

else

end if




(ased on the current value of gamelivesis, a reasona(le THE! E9%E statement might (e$

if ( gamelives > 0 ) thenwrite (*,*) "Still Alive, Keep Going!"

else if ( gamelives < 0 )write (*,*) "Sorry, game over."

else write (*,*) "Extra Life Granted."gameslives = 1

end if

8hich will displa' the message -%till live, Geep oing if the value of gamelivesis greater than 0,

displa' the message -%orr', game over if the value of game lives is Z 0, and displa' the message-E+tra 9ife ranted if the value of gamelivesis eAual to 0.


53/179


8.$ ,xam"le &ne

s previousl' descri(ed, writing or developing programs is easier when following a methodolog'. s

the program (ecome more comple+, using a clear methodolog' is even more important. The mainsteps in the methodolog' are$

"nderstand the /ro(lem :reate the lgorithm ;evelop the /rogram Test;e(ug the /rogram

To help demonstrate this process in detail, these steps will (e applied to a familiar pro(lem as an

e+ample. The e+ample pro(lem is to calculate the solution of a Auadratic eAuation in the form$

a x2+ b x+ c ,

Each of the steps, as applied to this pro(lem will (e reviewed.

6.4.1 8n'erstan' the Problem

>efore creating a solution, it is important to understand the pro(lem. Ensuring a complete

understanding of the pro(lem can help reduce errors.

t is )nown that the solution to the Auadratic eAuation is as follows$

xb

(b24 a c)

2 a

n the Auadratic eAuation, the term b2


54/179


The relationship (etween the discriminant and the t'pes of solutions two different solutions, one

repeated solution, or no real solutions4 is summari@ed in the (elow ta(le$

)o$itive Di$criminant Eero Di$criminant egative Di$criminant

Two real solutions =ne real solution Two comple+ solutions

E+ample$

3+2+3E+ample$

2+2


55/179


56/179


! display complex root1 and root2if ( discriminant < 0 ) then

root1 = -b / (2.0 * a)root2 = sqrt(abs(discriminant)) / (2.0 * a)

write(*,*) "This equation has two real roots:"write(*,*) "root 1 = ", root1, "+i", root2

write(*,*) "root 2 = ", root1, "-i", root2end if

end program quadratic

The indentation is not reAuired, (ut does help ma)e the program easier to read.

6.4.4 0est9Debug the Program

=nce the program is written, testing should (e performed to ensure that the program wor)s. The

testing will (e (ased on the specific parameters of the program. n this e+ample, each of the three

possi(le values for the discriminant should (e tested.

C:\mydir> quadQuadratic Equation Solver ProgramEnter A, B, and C values2 4 2This equation has one root:root = -1.0000000

C:\mydir> quadQuadratic Equation Solver Program

Enter A, B, and C values3 9 3This equation has two real roots:root 1 = -0.38196602root 2 = -2.6180339

C:\mydir> quadQuadratic Equation Solver ProgramEnter A, B, and C values3 3 3This equation has two real roots:root 1 = -0.50000000 +i 0.86602539root 2 = -0.50000000 -i 0.86602539C:\mydir>

dditionall', these results can (e verified with a calculator.

8.5 ',L,CT C%', 'tatement

%E9E:T :%E statement, often referred to as a :%E statement, is used to compare a given value

with preselected constants and ta)e an action according to the first constant to match. :%E

statement can (e hand' to select (etween a series of different possi(ilities or cases.


57/179


The select case varia(le or e+pression must (e of t'pe integer, character, or logical. real t'pe is not

allowed. >ased on the selector, a set of one or more of ortran statements can (e e+ecuted.

The general format of the %E9E:T :%E statement is$

select case (variable)

case (selector-1)

case (selector-2)...

case (selector-n) case default end select

where Zfortran statements461[, Zfortran statements462[, Zfortran statements463[, ..., Zfortran

statements46n[ and Zfortran statements46default[ are seAuences of one or more e+ecuta(le statements.The selector61, selector62, selector63, ..., and selector6n are called selector lists. Each :%E selector

list ma' contain a list andor range of integers, character or logical constants, whose values ma' not

overlap within or (etween selectors. selector6list is either a single or list of values, separated ('commas. Each selector list must (e one of the following forms.

( value )( value-1 : value-2 )( value-1 : )( : value-2 )

where value, value61 and value62 are constants or literals. The t'pe of these constants must (e identical

to that of the selector.

The first form has onl' one value

The second form means all values in the range of value61 and value62 inclusive4. n this form,

value61 must (e less than value62

The third form means all values that are greater than or eAual to value61

The fourth form means all values that are less than or eAual to value62

n order, each selector e+pression is evaluated. f the varia(le value is the selector or in the selector

range, then the seAuence of statements in Zfortran statements4[ are e+ecuted.

f the result is not in an' one of the selectors, there are two possi(ilities$

if :%E ;E"9T is there, then the seAuence of statements in statements6;E"9T aree+ecuted, followed (' the statement following E!; %E9E:T

if the :%E ;E"9T is not there, the statement following E!; %E9E:T is e+ecuted

The constants listed in selectors must (e uniAue. The :%E ;E"9T is optional. >ut with a :%E

;E"9T, 'ou are guaranteed that whatever the selector value, one of the la(els will (e used. The


58/179


place for :%E ;E"9T can (e an'where within a %E9E:T :%E statementP however, putting it at

the end would (e more natural.

or e+ample, given the declarations,

integer :: hours24, hours12character(2) :: ampm

the following case statement,

select case (hours24)case (0)

hours12 = 12ampm = "am"

case (1:11)hours12 = hours24ampm = "am"

case (12)hours12 = hours24

ampm = "pm"case (1:11)

hours12 = hours24 - 12ampm = "pm"

end select

might (e useful for to convert 2


59/179


8.0 ,xam"le T*o

t'pical pro(lem is to assign grades (ased on a t'pical grading standard.

6.&.1 8n'erstan' the Problem

or this e+ample, the program will assign grades using the following grade scale$

> : ;

[U0 C0 6 C B0 6 B 0 6 ZU5

The program will read three test scores, compute the average, and displa' the appropriate grade (asedon the average.

6.&.2 Create the lgorithm

The algorithm is the name for the ordered seAuence of steps involved in solving the pro(lem.

or this pro(lem, the varia(les will (e declared and an initial header displa'ed. Then, the test1, test2,

and test2values will need to (e read from the user.

! declare variables! reals -> test1, test2, test2! integer -> testave! display initial header! read the test1, test2, and test2 values

!e+t, the average can (e calculated. The average will (e converted to the nearest integer and, (ased onthat, the appropriate grade can (e determined and displa'ed. ormali@ing this, the following steps can

(e developed.

! calculate the testave and convert to integer! determine grade! A - >= 90! B - 80 to 89! C - 70 to 79! D - 60 to 69! F - ased on the algorithm, the following program can (e created.

program grades

! declare variablesimplicit none


60/179


real :: test1, test2, test2integer :: testave

! display initial headerwrite (*,*) "Grade Assignment Program"write (*,*)

write (*,*) "Enter test 1, test 2 and test 3 values"

! read the test1, test2, and test2 valuesread (*,*) test1, test2, test3

! calculate the average and convert to integertestave = nint ((test1 + test2 + test3)/3.0)

! determine grade! A >= 90, B 80-89, C 70-79, D 60-69, F gradeGrade Assignment Program

Enter test 1, test 2 and test 3 values70 80 90Grade is: B

C:\mydir>

The program should (e tested with a series of data items to ensure appropriate grade assignment foreach grade. Test values for each grade should (e entered for the testing.

50


61/179


8. ,xercises


6.5.1 Quiz Questions


14 9ist the si+ relational operatorsN

24 9ist the three (asic logical operatorsN

34 or each of the following, answer .true. or .:a&$e. in the space provided.

boolean :: b1 = .true., b2=.false., b3=.true.integer :: i=5, j=10

( b1 .or. b2 ) ______________

( b1 .or. b3 ) ______________

( b1 .and. b2 ) ______________

( b1 .and. b3 ) ______________

( (b1 .or. b2) .and. b3 ) ______________

( b1 .or. (b2 .and. b3) ) ______________

( .not. ( i < j ) ) ______________

( j < i ) ______________

,.,

51


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63/179


B4 8rite a ortran to program that reads a num(er from the user that represents a television

channel and then uses a :%E construct to determine the call letters for that station.

Channe& Ca&& +etter$ ::i&iation

3 GV>: !>:

5 GVV" =

C G9% :>%

10 G9V /u(lic

13 GT!V >:

The program should displa' an appropriate message if an invalid or unassigned channel is

entered. Test the program on a series of input values that will show each station.

53


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5


65/179

9 Loo"ing

8hen a series of ortran statements need to (e repeated, it is referred to as a loopor do$loop.

ortran do$loopis a special control statement that allows a ortran statement or set of statements to (ee+ecuted multiple times. This repetition can (e (ased on a set num(er of times, referred to as counter

controlled, or (ased on a logical condition, referred to as conditionall' controlled. Each of these

looping methods is e+plained in the following sections.

9.1 Counter Controlled Loo"ing

counter controlled loop is repeats a series of one or more ortran statements a set num(er of times.

The general format of the counting loop is$

do count_variable = start, stop, step

end do

where the count varia(le must (e an integer varia(le, start, stop, and step are integer varia(les or

integer e+pressions. The step value is optional. f it is omitted, the default value is 1. f used, the stepvalue cannot (e @ero. The Zfortran statements4[ is a seAuence of statements and is referred to as the

bod%of the do6loop. #ou can use an' e+ecuta(le statement within a do6loop, including 6THE!6

E9%E6E!; and even another do6loop. >efore the do6loop starts, the values of start, stop, and stepare computed e+actl' once. Iore precisel', during the course of e+ecuting the do6loop, these values

will not (e re6computed.

The count varia(le receives the value of start varia(le or e+pression. f the value of control6var is less

than or eAual to the value of stop6value, the Zfortran statements4[ part is e+ecuted. Then, the value ofstep 1 if omitted4 is added to the value of control6var. t the end, the loop goes (ac) to the top and

compares the values of control6var and stop6value.

f the value of control6var is greater than the value of final6value, the do$loopcompletes and the

statement following end dois e+ecuted.

or e+ample, with the declarations,

integer :: counter, init=1, final=10, sum=0

the following do6loop,

do counter = init, finalsum = sum + counter

end dowrite (*,*) "Sum is: ", sum

will add the num(ers (etween 1 and 10 which will result in 55. %ince the step was not specified, it is

defaulted 1.

55


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:hapter K 9ooping

nother e+ample, with the declarations,

integer :: counter, init=1, final=10, step=2

and the following do6loop,

do counter = init, final, step

write (*,*) counterend do

will displa' the odd num(ers (etween 1 and 10 1, 3, 5, B, 4.

nother e+ample would (e to read some num(ers from the user and compute the sum and average of

those num(ers. The e+ample as)s the user how man' num(ers, reads that man' num(ers, computesthe sum, and the computes the average, and displa's the results.

program averageimplicit noneinteger :: count, number, sum, input

real :: average

write(*,*) "Enter count of numbers to read"read(*,*) count

sum = 0do number = 1, count

read(*,*) inputsum = sum + input

end do

average = real(sum) / real(count)write *(*,*) "Average = ", average

end program average

The use of the function real)*converts the sum and count varia(les from integers to real values asreAuired for the average calculation. 8ithout this conversion, sumcount division would (e interpreted

as dividing an integer (' an integer, 'ielding an integer result.

final e+ample of a counter controlled loop is to compute the factorial of a positive integer. The

factorial of an integer n, written as n\, is defined to (e the product of 1, 2, 3, ..., n61, and n. Ioreprecisel', n\ U 1 Y 2 Y 3 Y ... Y n.

integer :: factorial, n, i

factorial = 1do i = 1, n

factorial = factorial * iend do

the a(ove do6loop iterates ntimes. The first iteration multiplies factorial with 1, the second iterationmultiplies factorial with 2, the third time with 3, ..., the i thtime with iand so on. Thus, the values that

are multiplied with the initial value of factorial are 1, 2, 3, ..., n. t the end of the do6loop, the value of

factorial is 1 Y 2 Y 3 Y ... Y nwhich is n.

5


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:hapter M 9ooping

9. ,IT and C:CL, 'tatements

The e+it and c'cle statements are used to modif' the e+ecution of a do6loop. The exitstatement is used

to e+it a loop. The e+it can (e used alone, (ut it is t'picall' used with a conditional statement to allowe+iting a loop (ased on a specific condition. The exitstatement can (e used in a counter controlled

loop or a conditionall' controlled loop.

or e+ample, given the following declarations,

integer :: i

the following loop,

do i = 1, 10if (i == 5) exit

write(*,*) iend do

will displa' the num(ers from 1 to < s)ipping the remaining iterations. %ince the varia(le iis chec)ed(efore the write statement, the value is not displa'ed with iis 5 and the loop is e+ited without

completing the remaining iterations.

The c%clestatement will s)ip the remaining portion of the do6loop and start (ac) at the top. The c%cle

statement can (e used in a counter controlled loop or a conditionall' controlled loop. f the c'clestatement is used within a counter controlled loop, the ne+t inde+ counter is updated to the ne+t

iteration, which could terminate the loop.

9.! Counter Controlled ,xam"le

n this e+ample we will write a ortran program to find the difference (etween the sum of the sAuares

and the sAuare of the sum of the first&natural num(ers.

:.3.1 8n'erstan' the Problem

n order to find the difference (etween the sum of the sAuares and the sAuare of the sum of the first&

natural num(ers, we will need to find (oth the sum of the sAuares and the sAuare of the sum. or

e+ample, the sum of the sAuares of the first ten natural num(ers is,

12

22

102

= 3C5

The sAuare of the sum of the first ten natural num(ers is,

1 2 102 = 552 = 3025

Hence the difference (etween the sum of the sAuares of the first ten natural num(ers and the sAuare ofthe sum is 3025 6 3C5 U 2


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:hapter K 9ooping

:.3.2 Create the lgorithm

or this pro(lem, first we will need to read the&value. Then, we will loop from 1 to the&value and

find (oth the sum of the sAuares and the sAuare of the sum.

! declare variables! integer -> i, j, n, SumOfSqrs, SqrOfSums! display initial header! prompt for and read the n value! loop from 1 to N! compute sum of squares! compute sums! square the sums! compute difference between sum of squares and square of sums! display results

or convenience, the steps are written a program comments.

:.3.3 Deelop the Program

>ased on the algorithm, the (elow program could (e developed.

program difference

! declare variablesimplicit noneinteger :: i, n, SumOfSqrs=0, SqrOfSums=0, difference

! display initial headerwrite(*,*) "Example Program"

write(*,*) " Difference between sum of squares "write(*,*) " and square of sums"write(*,*)

! prompt for and read the n valuewrite(*,*) "Enter N value: "read(*,*) n

! loop from 1 to N

do i = 1, n! compute sum of squaresSumOfSqrs = SumOfSqrs + i**2

! compute square of sumsSqrOfSums = SqrOfSums + i

end do

! square the sumsSqrOfSums = SqrOfSums**2

! compute difference between sum of squares and square of sumsdifference = SqrOfSums - SumOfSqrs

5C


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:hapter M 9ooping

! display resultswrite(*,*) "Difference: ", difference

end program difference

The spacing and indentation is not reAuired, (ut helps to ma)e the program more easil' reada(le.

:.3.4 0est9Debug the Program

or this pro(lem, the testing would (e to ensure that the results match the e+pected value. %ome

e+pected results can (e determined with a calculator or a spreadsheet. f the program does not provided

the correct result, one or (oth of the intermediate results,!um'f!qrsor!qr'f!ums, ma' (e incorrect.These values can (e displa'ed with a temporar' write statement to determine which might not (e

correct. f the pro(lem is still not found, the intermediate values calculated during the loop can also (e

displa'ed with a write statement. The output can (e reviewed to determine what the program is doing

and what ma' (e wrong4.

9.$ Conditional Controlled Loo"ing

conditional controlled loop repeats a series of one or more ortran statements (ased on a condition.s such, the loop ma' e+ecute a indeterminate num(er of times.

=ne form of the conditional loop is$

do while (logical expression)

end do

n this form, the logical e+pression is re6chec)ed at the top of the loop on each iteration.

more general format of the conditional loop is$

do

end do

s is, this loop will continue forever. /ro(a(l' not so good. selection statement, such as an statement, and an exitstatement would (e used to provide an means to terminate the looping. or

e+ample,

doif (logical expression) exit

end do

8ould stop looping onl' when the logical e+pression evaluates to true. The e+it statement can used

used in multiple times in different locations as needed. n statement, in an' form, can (e used foreither the e+it of c'cle statements.

5


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:hapter K 9ooping

or e+ample, a conditional loop could (e used to reAuest input from the user and )eep re6prompting

until the input is correct.

integer :: month

do write (*,*) "Enter month (1-12): "read (*,*) monthif (month >= 1 .and. month


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:hapter M 9ooping

unless the 'ears is evenl' divisi(le (' month, date, year! display initial header

! loop! request month, date, and year! read month, date, and year! check month (1-12)! check year (1970-2020)! check date! 1,3,5,7,8,10,12 31 days! 4,6,9,11 30 days! 2 if modulo of year/4 is 0 29 days ! 2 if modulo of year/4 is /= 0 28 days ! display results


:.-.3 Deelop the Program


program datecheck

! declare variablesimplicit noneinteger :: month, date, year, datemax

! display initial header

write(*,*) "Date Verification Example"

! loopdo

! request month, date, and yearwrite(*,*) "Date Verification Example"

! read month, date, and yearread (*,*) month, date, year

! check month (1-12)if ( month < 1 .or. month > 12 ) then

write(*,*) "Error, invalid month"

cycleend if

! check year (1970-2020)if ( year < 1970 .or. year > 2020 ) then

write(*,*) "Error, invalid year"cycle

end if

! check date

1


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:hapter K 9ooping

! 1,3,5,7,8,10,12 31 days! 4,6,9,11 30 days! 2 if modulo of year/4 is 0 29 days ! 2 if modulo of year/4 is /= 0 28 days

select case (month)

case (1,3,5,7,8,10,12)datemax = 31case (2)

if (mod(year,4)==0) thendatemax = 29

elsedatemax = 28

end ifcase (4,6,9,11)

datemax = 30end select

if ( date < 1 .or. date > datemax ) then

write (*,*) "Error, invalid date."cycle

end if

exitend do

! display resultswrite(*,*) "Valid Date is:", month, date, year

end program datecheck

The spacing and indentation is not reAuired, (ut helps to ma)e the program more easil' reada(le.

:.-.4 0est9Debug the Program

or this pro(lem, the testing would (e to ensure that the results match the e+pected value. This will

reAuire entering a series of different dates and verif'ing that the displa'ed output is correct for thegiven input data.

9.0 ,xercises


:.&.1 Quiz Questions


14 8hat happen when an exitstatement is e+ecutedN

24 How man' exitstatements can (e included in a loopN

34 8hat happen when an continuestatement is e+ecutedN

2


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74/179

:hapter K 9ooping

34 8rite a program to calculate the range that a (all would travel when it is thrown with an initial

velocit' v)and angle *. >ased on an initial velocit' provided (' the user, calculate the range

ever' 5 degrees for angles (etween 5 and C5 degrees. f we assume negligi(le air friction andignore the curvature of the earth, a (all that is thrown into the air from an' point on the earths

surface will follow a para(olic flight path.

The range distance(etween the initial origin and

final impact4 is determined (' the formula$

range

2v,

2

gco$ * $in*

where v)is the initial velocit' of the (all, ` is the angle of the throw, andgis the acceleration

due to the earth7s gravit'. The value for gravit' should (e defined as a constant and set to 6.C1meters per second.

+ote, the intrinsic trigonometric functions wor) in radians, so the angle in degrees will need to

(e converted to radians for the calculations. To convert degrees to radians$

radians degrees

1*,

Test the program on a series of different input values.

sumsExample Program Difference between sum of squares and square of sums

Enter count of numbers to read:3Difference: 2640

8hen the advance clause is included, with the setting of -no as follows$

! prompt for and read the n valuewrite(*,*, advance="no") "Enter N value: "read(*,*) n

The resulting e+ecution would (e as follows$

c:\mydir> sumsExample Program Difference between sum of squares and square of sums

Enter count of numbers to read: 10Difference: 2640

8hich allows the input to (e entered on the same line as the prompt.

1;.8 ,xam"le

This e+ample will read a date from the user month, date, and 'ear, on the same line4, determine the

da' of wee) for that monthdate'ear4. Then, the program will displa' the original input date numericform4 and the formatted date. The original input date will (e displa'ed include leading 07s i.e.,

010120104.

1;.6.1 8n'erstan' the Problem

or this pro(lem, we will read the three num(ers for the date from the user. The verification of the date

information is left as an e+ercise.


80/179

:hapter 10 K ormatted nput=utput

To calculate the da' on which a particular date falls, the following algorithm ma' (e used the divisions

are integer divisions4$

a = (14 - month) / 12y = year - a

m = month + 12*a - 2

daynum = [ date + y + y/4 - y/100 + y/400 + (31*m/12) ] mod 7

The value of da#numis 0 for a %unda', 1 for a Ionda', 2 for a Tuesda', etc.

1;.6.2 Create the lgorithm

or this pro(lem, first we will need to read the date. The verification of the date entered and error

chec)ing is left as an e+ercise. Then, the original input date can (e displa'ed, in numeric form,formatted appropriatel'. or a date, this would mean two digits for the month, a -, two digits for the

date, a -, and four digits for the 'ear. 8hen the date is onl' one digit, for e+ample 5, it is customar'

to displa' a -05 so the program will ensure this occurs.

! declare variables! integer -> month, date, year! display initial header! prompt for month, date, and year! read month, date, and year! display formatted numeric month/date/year

Then the program can calculate the da' of the wee) (ased on the formula4 and convert the resulting

num(er 064 into a date string and displa' the result.

! calculate day of week

! convert day of week (0-6) to string! convert month (1-12) to string! display formatted string for day, month, and year


1;.6.3 Deelop the Program


program dateformatter

! declare variablesimplicit noneinteger :: month, date, yearinteger :: a, m, y, d,character(9) :: amonth, day_of_week

! ----------! display initial header

write(*,*) "Date Formatting Example"

B0


81/179

:hapter 10 M ormatted nput=utput

! prompt for month, date, and yearwrite(*,*,advance="no") "Enter date (month, date, year):"

! read month, date, and yearread (*,*) month, date, year

! ----------! display formatted numeric month/date/year

write(*,*) "----------------------------------------"write(*,*) "Input Date: "write(*,'(5x, i2.2, a, i2.2, a, i4)', imonth, "/", &idate, "/", iyear

! ----------! calculate day of week

a = (14 - imonth) / 12

y = iyear - am = imonth + 12 * a - 2d = mod ( (idate + y + y/4 - y/100 + y/400 + (31*m/12)), 7)

! ----------! convert day-of-week integer to day-of-week string

select case (d)case (0)

day_of_week = "Sunday "case (1)

day_of_week = "Monday "case (2)

day_of_week = "Tuesday "case (3)

day_of_week = "Wednesday"case (4)

day_of_week = "Thursday "case (5)

day_of_week = "Friday "case (6)

day_of_week = "Saturday "end select

! ----------! convert month (1-12) to string

select case (month)case (1)

amonth = "January "case (2)

amonth = "February "case (3)

amonth = "March "case (4)

amonth = "April "

B1


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case (5)amonth = "May "

case (6)amonth = "June "

case (7)

amonth = "July "case (8)amonth = "August "

case (9)amonth = "September"

case (10)amonth = "October "

case (11)amonth = "November "

case (12)amonth = "December "

end select

! ----------! display formatted string for day, month, and year

write(*,'(/a)') "Formatted Date:"write(*,'(5x, a, a, a, 1x, i2.0, a, i4/)') &

trim(day_of_week), ", ", trim(smonth), &idate, ", ", iyear

end program dateformatter

The spacing and indentation is not reAuired, (ut helps to ma)e the program more easil' reada(le. The

trim)*intrinsic function removes an' trailing spaces from the input string. dditional informationregarding handling character data t'pes in provided in the following section.

1;.6.4 0est9Debug the Program

or this pro(lem, the testing would (e to ensure that the output formatting is correct. %ince there is noerror chec)ing on the input, onl' correct dates should (e entered. Test the program on a series of

different input values and verif' that the output is correct for those input values.

1;.9 ,xercises


1;.:.1 Quiz Questions


14 8hat is the format specifier for each of the following$

a4 integer values

(4 real valuesc4 logical values

d4 hori@ontal spacing i.e., spaces4

B2


83/179

:hapter 10 M ormatted nput=utput

e4 a newline

f4 charactersstrings

24 ;escri(e the output of the following code fragment 1 pts each4$

+ote, show (lan)s with an R underscore4 character.

write (*,'(a5)') "Hello World"write (*,'(a)') "Hello World"

34 ;escri(e the output of the following code fragment 3 pts4$

!ote, show (lan)s with an R underscore4 character.integer :: number = 5

write (*,'(i5.3)') number


84/179


34 8rite a ortran program that displa's an amorti@ation schedule. The program should read the

loan amount, annual interest rate, and the loan term in months from a single line4.

The formula for calculating the monthl' pa'ment is$

pa#ment amount

irate(

1+ irate)

term

( (

1+

irate)

term

1)

+ote, the iratein the formula must (e converted to a monthl' rate divided (' 124 and then

divided (' 100 to convert from percentage4. ;uring the time period term4, some of each

monthl' pa'ment will (e used to pa' the interest and some will (e used to reduce the

outstanding (alance. The monthl' interest amount can (e calculated (' monthl' interest ratetimes outstanding (alance. The amounts must (e lined up with onl' two digits for cents. The

pa'ment num(er must three digits including leading @ero7s if necessar'4. Test the program on a

series of different input values and verif' that the output is correct for those input values.


85/179

11 Characters and 'trings

ortran was originall' developed for scientific and engineering application reAuiring significant

mathematical calculations. However, the ortran 5 language includes e+tensive character and stringhandling capa(ilities.

11.1 Character and 'tring Constants

character is a single character or s'm(ol, t'picall' enclosed in Auotes. or e+ample, letters -6Wand -a 6 -@4, punctuation -\, -,, -N, etc.4 , s'm(ols, -S, -, -[, etc.4, and digits -1, -2 are

characters.

%ome e+amples include$

"X""z""5"

:haracter and string constants are case sensitive. %o, character - upper6case4 is not the same as -+

lower6case4. 8hen a digit is enclosed in Auotes, it is treated as a character and conseAuentl'

arithmetic operations addition, su(traction, etc.4 are not allowed.

string is a series of characters. string consists of an ar(itrar' seAuence of characters also enclosed

in Auotes. %ome e+amples include$

"Hello World.""456"

"1 2 3""456?""Good bye cruel world!!""Have a nice day?"

%ince digits enclosed in Auotes are not numeric values, the strings -1 2 3 and -


86/179

:hapter 11 K :haracters and %trings

This is performed with a t'pe declaration statement in the form of$

::

or character varia(les, the t'pe is -character. or e+ample, to define an character varia(le to hold the

da' of wee) i.e., -8ednesda'4, the following declaration,

character(len=9) :: dayofweek

8ould define the varia(le, da%o("ee-, with a ma+imum length of possi(le characters.


character(len=3) :: symbol1, symbol2character :: symbol3character(1) :: symbol5, symbol5character(30) :: symbol6, symbol7

The declarations can (e entered in an' order, however the' must (e at the (eginning of the program.

The -lenU is optional and can (e omitted. 8hen the length is omitted entirel', the default length is setto 1. This, -character, -characterlenU14, and -character14 are all the same.

8hen multiple varia(les are included in a single declaration, the' must all (e the same length. f

different lengths are reAuired, separate declaration lines are reAuired.

11.! Character 3ariable Initiali(ation

t is possi(le to declare a character varia(le and to set it is initial value at the same time. This

initiali@ation is not reAuired, (ut can sometime (e convenient. or e+ample, to define an charactervaria(le, da%o("ee-, and set it to a da' of wee)$

character(len=9) :: todaysdate="Wednesday"


character(9) :: thismonth="June", lastmonth, nextmonth="July"character :: ltr1="A", ltr2="b"

%paces or no spaces (etween the varia(les, eAual signs, semicolons, and commas are allowed.Varia(les initiali@ed at declaration can (e changed during program e+ecution as needed.

11.$ Character Constants

t is possi(le to declare a character varia(le, set it is initial value, and ensure that the value can not (e

changed. or e+ample, to define an character constant, lang,

character(len=7), parameter :: lang="English"

To save counting the characters, the -Y can (e used. or e+ample,

character(len=*), parameter :: university="UNLV"

This instructs the ortran compiler to count the characters and set the appropriate length.

B


87/179


88/179

:hapter 11 K :haracters and %trings

11.8 Character Com"arisons

The standard relational operators -UU, -[, -[U, etc.4 have some limitations when character data is

used. %imple comparisons, such as,

"A" < "D""ABC" == "ABC"

will wor) as e+pected. That is, (oth will evaluate to true.

However, when comparing, the following characters,

"A" > "a""100" < "20""ABC"


89/179

:hapter 11 M :haracters and %trings

11.1; ,xam"le

This e+ample will scan a string and convert all lower6case letter to upper6case.

11.

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