Introduction to Fortran

Programming

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The IF Statement

Do Loops

Formatted output

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Introduction

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Getting started

Program Structure

Fortran Statements

Declarations

Opening files

Quiz

Home

Introduction

Program Structure

Getting Started

Fortran Statements

DeclarationsOpening

FilesReading

Data

The IF Statement DO Loops

OutputCompilatingRun

Program

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Introduction

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Program Structure

Fortran Statements

Declarations

Opening files

Quiz

Learning Objectives

The goal of this Fortran learning module is to give a quick introduction to the most common features of the Fortran 77 programming language

This includes Declarations Open external files Read input data Loops Format statements Compilating Run program

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Introduction

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Program Structure

Fortran Statements

Declarations

Opening files

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Introduction

Fortran is a general purpose programming language, mainly intended for mathematical computations in e.g. engineering.

Fortran is an acronym for FORmula TRANslation, and was originally capitalized as FORTRAN.

Fortran was the first ever high-level programming languages. The work on Fortran started in the 1950's at IBM and there have been many versions since.

By convention, a Fortran version is denoted by the last two digits of the year the standard was proposed.

We will be using Fortran 77.Why Fortran?

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Program Structure

Fortran Statements

Declarations

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Getting started

Log on a UNIX server, in our case Petra

In the terminal window, start emacs followed by the name you wish to give your program. Fortran files are always denoted by .f

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Fortran Statements

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Structure of a Program

This is the structure of a main program:

program name declarations statements stop end

In the name field, it is customary to use the same name as the Fortranfile has

A program must always end with end

Microsoft Word

Document

Here’s a Fortran Template that contains the most elementary

Arithmetic Operators in Fortran

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Introduction

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Program Structure

Fortran Statements

Declarations

Opening files

Quiz

Fortran Statements

Fortran77 programs are typed in lines of up to 72 characters, with the first six columns of each line reserved for special purposes. As a result, Fortran77 statements ALWAYS BEGIN AT, ALWAYS BEGIN AT, OR AFTER, COLUMN 7. OR AFTER, COLUMN 7.

In emacs, the TAB key will bring you to column 7

If the firstfirst columncolumn contains ”c” or a ”*”, the the entire line would be treated as a comment.

A line can only contain 72 characters, but you will often see yourself in need of more space

A ”*” in the 6th6th columncolumn specifies that this line is a continuation of the previous

Column Position Rules

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Fortran Statements

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Declarations

A Fortran program always starts with declaring which variables you will be using. A variable consists of 1-6 characters chosen from the letters a-z and the digits 0-9.

List of Fortran data types integer list of variables real list of variables character list of variables logical list of variables complex list of variables

See an exampleSee an example

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Program Structure

Fortran Statements

Declarations

Opening files

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Opening External Files

Very often you need a large amount of input data and you wish to use your output data to make a chart or a graph etc

It is then very useful to have external output and input files.

Syntax used can be viewed

It is customary to open the output file together with the input file, even though it may not be written to at once

Example

Here

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Fortran Statements

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Reading Data

Two ways of reading input data:1) From file2) From screen

1) Reading input data from file: First, input file must be open (see opening external files)

Then, the command is:READ(<unit number>, <format>) list of variablesUnit number is the same one as was assigned to the file when opening, format is discussed here, but it is common to use *, which means free format. After the bracket, the variables listed in the input file should be listed, in the proper order.

Read Data from Screen

Example

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Read Data from Screen

2) Read data from screenIn order to read data from screen, you must first make the program ask for input data. Such a command may be:PRINT *, ’<request for input>’

The PRINT command prints to screen, * is still free format followed by a statement

When this has been done, the program must read the inputREAD *, <variable>

The READ command allocates the input data to the pre-declaredvariable <variable>

Confused? This example should clear things up

Example

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Fortran Statements

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Opening files

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The IF Statement

An important part of any programming language are the conditional statements. The most common such statement in Fortran is the if statement, which actually has several forms.

The simplest one is the logical if statement: IF (logical expression) executable statement

It says that if something is true, do something

If you wish to include several statements, the general form is:

IF (logical expression) THEN statements ELSEIF (logical expression) THEN statements : :ELSE statements ENDIF

What is a logical expression?

Click to know more

See an example on the use of the if statement

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Introduction

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Program Structure

Fortran Statements

Declarations

Opening files

Quiz

DO Loops

The repetition of a number of statements a predetermined number of times is so important that Fortran contains a special construction that allows this to be done.

In general, a ”DO loop" may contain any Fortran statements, including another do statement, known as a "nested DO loops".

The syntax is: DO 100 INDEX=int1,int2[,int3] 'statements'

100 CONTINUE

The number 100 is a statement label (More....)INDEX is a variable, and starts at int1 in steps of int3 and ends at int2For example, DO 100 MONTHS=1,N,6 would go through all

N months in steps of six. However, Steps are normally not included as you most of the time wish to run the loop for every step in the interval

DO loop Example

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Fortran Statements

Declarations

Opening files

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Formatted Output

When the program has calculated whatever it was supposed to calculate, it would be of no use if you dont get the results in a readable and understandable manner, and preferably to an external file so you can use your calculations in a graphical presentation etc

For this we will use the WRITE and FORMAT statements

Syntax:

WRITE(*, label) list-of-variables label FORMAT( format-code)

Explanations and Example

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Fortran Statements

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WRITE(*, label) list-of-variables label FORMAT( format-code)

Remember the statement label?

The wildcard * writes the result to screen, whereas a unit number would write to an external file assigned to this number.

A wide variety of format combinations exists.

Formatted Output

The Most Common

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Compilating

When your done writing your program, it’s time to compile your program.

What is a compilator?

We will use the following compilatorxlf -o prog fort.f

Simply write this in the UNIX terminal window. Fort.f is the name of the fortran file, if your file is called simple.f, you should write xlf –o prog simple.f

Hopefully nothing will happen, but most likely a list of errors is going to show

Errors in the Compilation Running your Program

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Run Program

When the compilation is complete it is time to run your program

Type ”prog” in your terminal window, and the program should run

If you made your program write the results to an output file, you may open the file and view the results

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This section includes a quiz on the topics covered by this module.

The quiz is meant as a control to see if you have learned some of the most important features

Hit object to start quiz (Depending on your connection, this may take a few seconds...)

Quiz

Shockwave Flash Object

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General information

Title: Introduction to Fortran

Teacher(s): Professor Jon Kleppe

Assistant(s): Per Jørgen Dahl Svendsen

Abstract: Provide a good background for solving problems within petroleum related topics using numerical methods

4 keywords: Fortran, loops, input/output, statments

Topic discipline: Petroleum Engineering

Level: 1

Prerequisites: None

Learning goals: Introduce the user to Fortran Programming

Size in megabytes: 0.9 MB

Software requirements: MS Power Point 2002 or later, Flash Player 6.0

Estimated time to complete:

Copyright information: The author has copyright to the module and use of the content must be in agreement with the responsible author or in agreement with http://www.learningjournals.net.

About the author

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FAQ

For Questions, try these Computer encyclopedias:

Dataleksikon

Webopedia

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Introduction

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Program Structure

Fortran Statements

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Opening files

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References

Fortran tutorial

Professional Programmer's Guide to Fortran77

Introduction to Fortran Programming

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Reading data

The IF Statement

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Formatted output

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Run Program

Introduction

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Getting started

Program Structure

Fortran Statements

Declarations

Opening files

Quiz

Summary

Subsequent to this module you should...

Have a basic understanding of how fortran is built up and how a FORTRAN program is constructed