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FORTRAN 77 Programming.

Lecture 1 : January 2001

Dr. Andrew Paul Myers

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Course Methods.

Lectures. Handout notes. Supervised practical work. Daily submission of exercises. Daily feedback on exercises. Model Answers. Final project. Weekly clinic for final Project.

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Introduction.

A course in FORTRAN 77. Why FORTRAN? Objectives :

• General education in computing.• Introduction to programming.• First write a simple program, then…• Write complex program.

Course Benefits :• I.T. is a part of all our lives and getting more

so!• FORTRAN and computing skills for other

courses.• Future employment.

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Tools For The Job.

Programming Environment :

CFS system and Exceed 6.2. Unix system (SG IRIX 6.5). Silicon Graphics Desktop Windows Text Editor (emacs). FORTRAN 77 Compiler (Mips 7.2.1). Workshop Debugger (cvd).

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Programming Languages. You are users! How computers work. Machine code. High level languages. Fortran : FORMula TRANslation. Other languages :

• Basic• C/C++• Pascal

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Programming Cycle.

Analyse the task. Plan the program, a structured

approach! Flowcharts & Dry running. Edit your source code. Compile and link program. Execute and debug program. Edit and recompile as necessary.

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IRIX f77 Compiler.

Edit source program (*.f) with “emacs” editor. Save file.

Compile and run on Unix command line in a shell window :/disk/n/gps> f77 –o test test.f

/disk/n/gps> test

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Simple Structure of A FORTRAN Program.

Program name. Declare variables and structures. Assign values to variables. Process data. Print results. End program.

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Flow of a Program.

Linear sequence. One command per line. Position on line : Very Important! Comments Statements (ignored). Repetition : Loops. Selections : Conditional statements. Always finish with an END statement.

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Position on a line.

The layout of FORTRAN program dates back to old 80 column punched cards, which were used for program input.

1 2-5 6 7-72 73-80

Total=x_value+y_value

& +z_value

C Comment line.

9 9999 FORMAT(‘Answer =‘,I4)

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Variable Declarations.

Variable names : Must be at least one alphabetic

character long, up to a maximum of 31 alphanumeric characters.

Must start with an alphabetic character. Case insensitive.

Alphanumeric characters are : a-z, 0-9 and the underscore ( _ ).

Implicit variables. I to N integers!

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Examples.

Valid names :• X

• THEDAY

• Min_cur

• Time28

Invalid names :• X*Z

• THE TIME

• 7YEARS

• _no_way$

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Basic Data Types.

REAL x=5.0 INTEGER i=20 COMPLEX z=(1.4,3.2) LOGICAL test=.TRUE. CHARACTER char=‘Hello’

More advanced data types can be made from these basic types.

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Declarations.

<Data Type> <variable> [,<variable(s)>]

e.g.

REAL x

REAL radius,volume

INTEGER loop,temp

CHARACTER string*10,name*30

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Parameters.

Parameters are constants, their value, once defined, can not be changed.

REAL g,pi

INTEGER days

PARAMETER (days=365)

PARAMETER (g=9.81,pi=3.142)

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Assignments.

<variable> = <value> | <variable> | <expression>

radius=2.5y=ztest=value+loop-tempvolume=(4.0*pi*radius**3.0)/3.0

Expressions follow the BODMAS precedence rule. Operators +, -, *, / and **

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Control Structures.

Basic building blocks of programs.

They control the flow of the program.

There are 3 different types :

Linear Sequence. Selection. Iteration or Loop.

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Other Statements.

PROGRAM [ program name ] END

C or * A comment.

PRINT*,’Hello’ PRINT*,’Value of X = ‘,x

This is free format output.

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Data Input.

Programs are useless without data! Use the READ statement to allow

users to input data. Prompt user for the data too!

e.g.

PRINT*,’Enter values for x & y :’

READ*,x,y

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Character Input.

A normal read statement can not be used to enter character variables. Use the following:

PRINT*,’Continue (y/n) : ‘

READ ‘(A1)’,yes_or_no

‘(A<n>)’ – <n> is the number of characters.

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Good Programming Style.

Comment your program! FORTRAN keywords in upper case. Variables in lower case. Use descriptive variable names. Blanks may be used to improve

readability. Indent code with “tabs”.

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General Program Layout.

PROGRAM [ program name ]

[ comments ]

[ declaration statements ]

[ executable statements ]

STOP

END

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References.

A Crash Course in FORTRAN 77.Donald M. Monro.(Edward Arnold).

Irix Insight On-line Help.SGI Developer Section.MIPSpro FORTRAN 77 Programmer’s guide.