Structured Programming Using Turbo BASIC

337 Pages·1988·14.696 MB·English

by  Wade Ellis and Ed Lodi (Auth.)

Structured Programming
Using Turbo BASIC
WADE ELLIS, JR. and ED LODI
West Valley College, Saratoga, California
@
ACADEMIC PRESS, INC.
Harcourt Brace Jovanovich, Publishers
Boston San Diego New York
Berkeley London Sydney
Tokyo Toronto
Copyright © 1988 by Academic Press, Inc.
All rights reserved.
No part of this publication may be reproduced or
transmitted in any form or by any means, electronic
or mechanical, including photocopy, recording, or
any information storage and retrieval system, without
permission in writing from the publisher.
ACADEMIC PRESS, INC.
1250 Sixth Avenue, San Diego, CA 92101
United Kingdom Edition published by
ACADEMIC PRESS INC. (LONDON) LTD.
24-28 Oval Road, London, NW1 7DX
Library of Congress Cataloging-in-Publication Data
Ellis, Wade.
Structured programming using Turbo BASIC/Wade Ellis, Jr., Ed
Lodi.
p. cm.
Includes index.
ISBN 0-12-237459-2 (hardcover)
ISBN 0-12-237460-6 (paperback)
1. BASIC (Computer program language) 2. Turbo BASIC (Computer
program) 3. Structured programming. I. Lodi, Ed. II. Title.
QA76.73.B3E44 1988
005. 13'3-dcl9 87-38268
CIP
88 89 90 91 9 8 7 6 5 4 3 2 1
Printed in the United States of America
PREFACE
Structured Programming Using Turbo BASIC is an introduction to modern
programming methods using the Turbo BASIC language. The book provides a
practical approach to these methods through examples and problems from both
business and mathematics. This approach allows you to learn programming while
also learning about graphics, files, and simulations—topics not always covered in
an introductory course.
The problem-solving strategy developed in this book uses the top-down,
structured programming method. This method consists of two main techniques:
repeatedly breaking a problem into smaller, more manageable tasks and using the
action block, the decision block, and the loop block—the three fundamental pro­
gramming structures—to perform each task. The use of subroutines or procedures
greatly facilitates the process of breaking a problem into smaller parts.
The style used to write programs is also an important part of the top-down
programming method. Correct indentation and spacing improve readability, and
internal descriptions of tasks make programs easier to follow and understand.
These concepts, along with subroutines, are emphasized in the book. They are
all introduced early and used throughout the book so that programs are easy
to read and understand. Some programming constructs are introduced using
graphics so that the tasks in a program can be connected with the resulting
picture to help in understanding how a structure works.
To understand all the fundamental structures of modern programming
methods, you would need to be familiar with the fundamentals of algebra. We
do include several challenging example programs and problems for those who have
xvi Preface
the interest and the necessary mathematical background. However, the only
prerequisites for using this book are a familiarity with arithmetic and a desire to
learn.
The book has an introduction and 12 chapters. The first chapter presents
the Turbo BASIC environment on an IBM PC (and compatible machines). The
next seven chapters cover fundamental programming structures and concepts.
Chapters 9 and 10 present the two data structures, arrays and files. The final
two chapters introduce advanced graphics topics and computer simulations. Each
chapter begins with a set of objectives followed by guided, hands-on computer
exercises in the Exploratory Activities section. A summary and extension of
these ideas is presented in the Concepts and Methods section. Beginning with
Chapter 2, several program examples are carefully developed to illuminate the
ideas studied in the chapter. Chapter 2 through 12 conclude with a variety of
review questions and problems.
To use this book you need the Turbo BASIC software package for the IBM
PC, MS-DOS or PC-DOS 2.0 or later, an IBM PC computer (or compatible),
one double-sided disk drive, a graphics adapter card (CGA, EGA, or equivalent),
and a suitable monitor.
If you have any questions about your equipment, you should consult your
dealer or the computer lab director.
This book can be used as a self-study guide to structured programming.
When you use the book in this way, we encourage you to work through all the
Exploratory Activities and Example Programs with great care.
This book can also be used in an introductory lecture course in business,
mathematics, or computer science. Students are encouraged to complete the
Exploratory Activities using a computer before those activities are discussed in
class. The first three chapters can be covered in one or two days each. The
remaining chapters could be covered in four to seven class meetings each. Certain
topics can be emphasized depending upon whether the course is taught from a
mathematical or business perspective.
Finally, the book can be used in an open-entry/open-exit computer lab­
oratory course. The student could work through the book in consultation with
the laboratory assistants, and several progress exams could be given along with
selected programming problems.
Acknowledgements
The authors would like to express their deep appreciation to several sources. Alice
Peters, editor, and Carolyn Artin, managing editor, at Academic Press, Boston,
gave us encouragement throughout the development, creation, and production of
this book. Deborah Wickenden, copy editor, contributed many suggestions and
corrections. The errors that remain are, of course, our own.
Preface xvii
We would also like to thank Herbert D. Peckham and Arthur Luehrmann
of Computer Literacy Press for giving us the opportunity and encouragement to
begin to write books on BASIC.
Finally, we are deeply grateful to our wives, Jane and Rose Marie, for their
patience and understanding throughout the writing and production of this book.
Wade Ellis, Jr.
Ed Lodi
the Computer Tutors of San Jose
P.O. Box 3709
Saratoga, CA 95070
INTRODUCTION
Computers are a part of our everyday activities—for example, many home ap­
pliances, automobiles, and office machines are controlled by computers. Govern­
ment institutions and banking firms use them to store, retrieve, and manipulate
information while industrial firms use them to solve manufacturing and scien-
tifc problems. Each of us can think of other ways in which computers are used
in our society. Moreover, you will probably be required to use a personal com­
puter or a computer terminal directly in your work. Most of the time you will
be using powerful computer programs that are available commercially. In such
cases, an understanding of programming provides a background that will allow
you to learn quickly how to use these software packages to their maximum poten­
tial. In addition, many of the commercially available packages such as EXCEL ,
dBASE III™, Rbase 5000™, and LOTUS 1-2-3® have programming capabilities
that require a programming background.
You may, at some time in your career, be given the responsibility for choos­
ing a software package to be used by your company. Programming experience,
obtained by working through this book, can give you the tools necessary to assess
the capabilities of competing products and will assist you in choosing the product
most appropriate for your company.
You may be entering a career path in business or science that requires
the regular use of computers at a high level of sophistication. The discipline of
structured programming provides a solid basis for developing the needed skills
for such careers.
2 Introduction
The Development of the Discipline of Structured Programming
The development of computer programming languages and methods began with
the first electronic computers in the early 1940s. As with the early development of
most things, the first programs were very successful but crude in comparison with
current software packages. Early programmers began to experience difficulties
getting their programs to run correctly as the length of the programs grew. The
process of ferreting out errors in these pioneering programs became more and
more difficult and tedious. The need for improved programming languages and
methods became apparent. Computer scientists developed a set of ideas for
systematically structuring programs to cope with difficulties encountered in using
early versions of computer languages.
The Development of Turbo BASIC
Professors Kemeny and Kurtz, working with students at Dartmouth College in
1963 and 1964, created the BASIC language to provide a programming environ­
ment that was easy to learn, had substantial computational power, and would
allow the user to enter information while the program was executing. They suc­
cessfully achieved their goal of bringing the use of computers within the reach of
college students and faculty. In so doing, they created a language that can be
easily used by professionals in business and science. The early versions of BASIC
had the same problems mentioned above. These problems were addressed by the
late 1970s with structured programming enhancements and graphics extensions
to the language. However, Dartmouth BASIC could run on only large mainframe
computers. At about this same time, versions of BASIC developed by Microsoft
Inc. appeared on microcomputers. These versions were necessarily small and
lacked the power of Dartmouth BASIC. In the mid-1980s, the size and speed
of microcomputers had developed to the point where a robust, fully functional
BASIC like Dartmouth BASIC could run effectively on them.
Borland International developed the Turbo BASIC language to take advan­
tage of the original concept of BASIC as a programming language while adding
structured programming concepts and their highly regarded programming en­
vironment. This language is easy to learn and has the structuring capabilities
required to write long programs with few, if any, errors. Turbo BASIC also has
strong graphics and data file handling facilities.
Structured Programming in Turbo BASIC
Turbo BASIC provides the necessary language structures for applying the dis­
cipline of structured programming. This book develops a method of writing
programs that uses the structuring facilities and the word processing capabilities
of Turbo BASIC to write programs that are well-structured, well-documented,
Introduction 3
and easy to understand and modify. You must be willing to think carefully about
problems away from the computer using paper and pencil to take full advantage
of this method. Even after you begin to use the computer to enter your programs,
the first step is to enter the general structure of the program. If you follow the
method presented in this book, you will develop the discipline and techniques
necessary to write long programs that can be easily modified or maintained by
you or others. In addition, you can use this disciplined approach to solve problems
with or without a computer.
How to Use This Book
Objectives are stated at the beginning of each chapter. Following these objectives,
Exploratory Activities are presented as guided exercises for you to complete using
your computer. It is important for you to work carefully through these exercises
to learn basic concepts and gain experience with the language environment. You
should attempt to answer any questions asked in these activities before proceed­
ing. Sometimes, you will be led through errors that can occur when using the
computer with Turbo BASIC. You will find the answers to some of the harder
questions in the text that follows the questions.
In the Concepts and Methods section that follows the Exploratory Activ­
ities, the concepts you worked with in the activities are discussed. Additional
material is presented in this section to enhance your understanding of the lan­
guage features of Turbo BASIC based upon your hands-on experience.
Starting in Chapter 2, the Example Programs section presents solutions to
typical programming problems, illustrating the concepts covered in the chapter.
All the example programs are written using the top-down structured program­
ming method.
At the end of every chapter except Chapter 1, there is a two-part section
called Exercises containing review questions and problems. The review questions
are intended to help you assess your understanding of the major concepts and lan­
guage features covered in the chapter. The answers to these questions appear in
Appendix A. The problems are intended to give you practice in developing solu­
tions that use the top-down structured method. They will focus on the concepts
and language features covered in the chapter. Solutions to the odd-numbered
problems appear in Appendix B.
Program Diskette for The Book
A program disk is available containing all of the Example Programs and many
of the programs in the Exploratory Activities. This disk will allow you to load
these programs from diskette rather than taking the time and effort to type them
in yourself. Each disk costs $5.00. For further information, please contact the
Computer Tutors, P.O. Box 3709, Saratoga, CA 95070.
CHAPTER 1
PROGRAMMING
ENVIRONMENT
A careful reading of the following objectives will give you an overview of the
material in this chapter. Keeping the objectives firmly in mind, you can proceed
through the chapter with confidence.
OBJECTIVES
Making a Work Disk
You will learn how to make a copy of the Turbo BASIC Program Disk to use as
your working diskette.
Booting up Turbo BASIC
You will learn how to enter the Turbo BASIC programming environment.
Using Your Computer
You will learn how to work with the Turbo BASIC programming environment to
enter and run programs.
6 Programming Environment
1—1 EXPLORATORY ACTIVITIES
Making a Working Diskette
You should always make working copies of software packages so that the original
master copy of the software can be used as a backup. If you already have a
working copy of Turbo BASIC, go on to the next section. If you have a hard disk
drive, consult Chapter 2 of the Turbo BASIC Owner's Handbook. If you have a
system with one disk drive, consult the DOS reference manual on formatting and
copying diskettes.
To make a working copy of the Turbo BASIC Program Disk that comes
with the Turbo BASIC package, place the DOS 2.0 (or later) diskette in drive
A and turn on the computer (the switch is at the right rear of the cabinet on
most computers). Turn on the monitor, if necessary. You may not see anything
displayed on the screen for 30 to 60 seconds. If your computer asks for the date
and time, enter them in the form requested or press the key marked [*-'[ twice if
you do not wish to enter them.
An A> should appear on the screen. The blinking underscore (_) next to
the A> is called the cursor. Notice that the slash symbol (/) is located on the
same key with the question mark symbol (?) on it. Now type
format b:/s
Note that the only space is between format and b. Now press I*—1!· The key
marked \+~*\is also referred to as the Enter key. Follow the directions displayed on
the screen by placing a blank diskette in drive B and press I*—1). The formatting
process will take a minute or so. When this process is complete, type N and
replace the DOS diskette in drive A with the Turbo BASIC Program Disk. To
place copies of the files you will need on your working disk, type
copy a:tb.exe b:
and press |*—'[. When this process is complete (in about 30 seconds), type the
following lines. Press I*—1! at the end of the first line and wait for the copy process
to end before typing the second line and pressing I*—1!.
copy a:tbhelp.tbh b:
copy a:hanoi.bas b:
Remove the Turbo BASIC Program Disk and store it in a safe place. Prepare a
label with the title "Turbo BASIC Work Disk." Remove the diskette in drive B
and place this label on it.