Guide to HTML, JavaScript and PHP for Scientists and Engineers [Brooks 2011-05-19].pdf

David R. Brooks

Guide to HTML, JavaScript

and PHP

For Scientists and Engineers

David R. Brooks

Institute for Earth Science Research and Education

2686 Overhill Drive

Eagleville, PA 19403

USA

brooksdr@drexel.edu

ISBN 978-0-85729-448-7

e-ISBN 978-0-85729-449-4

DOI 10.1007/978-0-85729-449-4

Springer London Dordrecht Heidelberg New York

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

Library of Congress Control Number: 2011926229

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as

permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced,

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or in the case of reprographic reproduction in accordance with the terms of licenses issued by the

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a speciic statement, that such names are exempt from the relevant laws and regulations and therefore

free for general use.

The publisher makes no representation, express or implied, with regard to the accuracy of the information

contained in this book and cannot accept any legal responsibility or liability for any errors or omissions

that may be made.

Printed on acid-free paper

Springer is part of Springer Science+Business Media (www.springer.com)

Preface

“The best way to become acquainted with a subject is to write

a book about it.”

—Benjamin Disraeli

“Each problem that I solved became a rule, which served

afterwards to solve other problems.”

—René Descartes

What Is the Purpose of This Book?

There are many students and professionals in science and engineering, other than those spe-

ciically interested in ields such as computer science or computer engineering, who need to

know how to solve computational problems on computers. There are basically two approaches

to meeting the needs of such people. One is to rely on software applications such as spread-

sheets, using built-in functions and perhaps user-deined macros, without requiring any

explicit understanding of the principles on which programming languages are based.

A second approach is to learn a programming language, previously Fortran or Pascal,

and more recently C, C++, or Java. These languages are important for certain kinds of

work, such as computer science or scientiic computing, but they may be viewed, possibly

with good reason, as irrelevant by many students and professionals.

From a student’s point of view, there is no painless solution to this dilemma, but in this

book I assume that learning to solve computational problems in an online environment

using HTML, 1 JavaScript , and PHP will at least appear to be a more relevant approach.

HTML and JavaScript are universally used for developing self-contained online applica-

tions. The use of PHP for accessing externally stored data iles, a capability that is not

available directly through JavaScript, greatly extends the range of science and engineering

problems that can be addressed. A working knowledge of these programming languages is

a valuable skill for any scientist or engineer. The fact that these are Web-based languages

may make such skills more immediately marketable than comparable skills developed

with older text-based languages.

1 See Glossary for definitions of terms appearing in bold font.

Preface

In some ways, the HTML/JavaScript/PHP environment is more dificult to learn than a

traditional text-based programming language such as C. C is a mature (some might prefer

“obsolete”), fairly small language with an unambiguous set of syntax rules and a primitive

text-based input/output interface. You can view the limitations of C as either a blessing or

a curse, depending on your needs. A major advantage of C is that programs written in

ANSI Standard C should work equally well on any computer that has a C compiler, making

the language inherently platform-independent .

HTML, JavaScript, and PHP, on the other hand, are immature and unstable program-

ming languages (if we can agree to call HTML a “language”) that function within a con-

stantly changing Web environment. There are dialects of HTML and JavaScript that will

work only on particular computing platforms and the possibility exists for language “exten-

sions” that may be even more platform-dependent. PHP is more platform-independent, but

it is still an evolving language whose standards are set and maintained by a user group –

essentially by volunteers. While it is true that there are extensions to languages such as C

and other older languages that are platform-dependent, the platform dependence of lan-

guages used in the online environment is a major implementation issue rather than an

occasional minor inconvenience.

As one indication of the teaching and learning challenges these environments provide,

just three popular paperback HTML and JavaScript reference books occupy nearly 6 in. of

space (15 cm in deference to a metric audience) on my ofice bookshelf! A great deal of

the material in those books is devoted to explaining the often subtle differences among

various versions of HTML and JavaScript.

Fortunately, it is possible to work with some core subsets of HTML and JavaScript

which, with PHP, can be used to solve some of the same kinds of computational problems

that would be appropriate for a more traditional language such as C or C++. My initial

motivation for writing this book was to learn how to use HTML, JavaScript, and PHP to

create my own online applications, and I now use this environment for many tasks that I

previously would have undertaken in C. Based on this experience, I have concluded that,

despite the fact that these languages cannot fairly be deined as “scientiic computing”

languages, it is nonetheless entirely reasonable to use them to learn basic programming

skills, and to create useful and robust science and engineering applications.

Although this book is intended for “scientists and engineers,” as suggested by its title,

the content is not technically complex. The examples and exercises do not require exten-

sive science, engineering, or mathematics background and only rarely is mathematics

beyond basic algebra needed. So, I believe this book could serve as a beginning program-

ming text for undergraduates and even for high school students.

Learning by Example

It is well known that people learn new skills in different ways. Personally, I learn best by

having a speciic goal and then studying examples that are related to that goal. Once I

understand those examples, I can incorporate them into my own work. I have used that

Preface

vii

learning model in this book, which contains many complete examples that can serve as

starting points for your work. (See the second quotation at the beginning of this preface.)

This model works particularly well in an online environment. The amount of online

information about HTML, JavaScript, and PHP, including code samples, is so vast that it

is only a slight exaggeration to state that nobody writes original code anymore. If you have

trouble “learning by example,” you will have trouble learning these languages, not just

from this book, but in general because that is how most of the available information is

presented.

It is an inescapable fact that a great deal of the source code behind Web pages involves

nothing more (or less) than creative cutting, pasting, and tweaking of existing code. Aside

from the issues of plagiarism and intellectual dishonesty that must be dealt with in an aca-

demic environment, there is also the practical matter of an effective learning strategy. You

cannot learn to solve your own computational problems just by trying to paste together

someone else’s work. (Believe me, I’ve tried!) Until you develop your own independent

skills, you will constantly be frustrated because you will never ind exactly what you need

to copy and you will be unable to synthesize what you need from what is available.

So, while you should expect to ind yourself constantly recycling your own code based

on what you learn from this book, you need to make sure that you really learn how to use

these languages and don’t just learn to copy !

If you are reading this book, you almost certainly are not and do not aspire to be a pro-

fessional programmer. For a casual programmer from a scientiic or technical background,

it can be very time consuming to cut through the clutter of online information about these

languages when the applications are not directly applicable to the needs of scientists and

engineers. In my own work, what I need over and over again is some sample code that will

jog my memory about how to approach recurring programming problems – how to select

items from a pull-down list, how to extract information from a data ile, how to pass infor-

mation from an HTML document to a PHP application, how to display data-based graph-

ics, etc. Throughout the book, I have tried to give examples that serve this need, including

an entire chapter devoted to PHP graphics.

iii

The Origin and Uses of This Book

In 2007, Springer published An Introduction to HTML and JavaScript for Scientists

and Engineers . This was followed in 2008 by An Introduction to PHP for Scientists and

Engineers: Beyond JavaScript . Those two books followed the sequence in which I learned

to use HTML, JavaScript, and PHP in my own work. (See the irst quotation at the begin-

ning of this preface.) When the time came to consider a second edition of the HTML and

JavaScript book, it seemed a better idea to undertake a rewrite that would combine both

books into a single volume. This book is the result. I have, hopefully, clariied some of the

explanations. There are more examples and exercises and I have added some new material

that my students and I have found useful, including a brief introduction to using “pseudo-

code” as an approach to organizing solutions to computing problems (see Appendix 4).

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