PASCAL plus data structures, algorithms, and advanced programming

657 Pages·1985·50.93 MB·English

by  Nell B Dale

.
Copyright © 1985 by D. C. Heath and Company.
All rights reserved. No part ofthis publication may be reproduced or
transluitted in any form or by any means, electronic or mechanical, including
photocopy, recording, or any information storage or retrieval system, without
perluission in writing from the publisher.
Published siInultaneously in Canada.
Printed in the United States ofAmerica.
International Standard Book Number: 0-669-07239-7
Library ofCongress Catalog Card Number: 84-82073
To the next generation ofcomputer scientists
N.D.
To my father, Mason M. Lilly
S.L.

Preface
Until recently there has not been much consensus among educators on
what formal education is necessary for a computer professional. It has al
ways beenconsideredessentialtohaveagreatdeal ofmathematicalknowl
edge, as \vell as an understanding ofcomputer hardware. Software educa
tion, however, often consisted ofthe teaching ofa number ofprogramming
languages. The development ofprogramming techniques, it was often as
sumed, was not a subjectofformal education, butratheramatterofexperi
ence. This situation is analagous to an English department teaching only
grammar without freshman cOlnposition, literature, or creative writing.
Today the shared experience ofa generation ofprogrammers has com
bined to form a body of practical and theoretical knowledge that can be
taughtalong with computer languages. Software is now an area ofstudy in
its own right. The evolution of this situation can be clearly seen in the
progression of computer science curricula advocated by the major com
puter professional organizations.
Three main professional organizations represent the spectrum of com
puter educators and professionals: the ACM (Association of Computing
Machinery), the IEEE (Institute of Electronic and Electrical Engineers),
and the DPMA (Data Processing Management Association). Each ofthese
organizations has contributed greatly to computer science education over
the years by publishingcurriculum guidelines that identify whata student
should know upon graduation from a four-year institution ofhigher learn
ing.
The first curriculum guidelines were published in 1968 by the ACM.
Theseguidelines assumedthatonlythose students whohadabroadmathe
matical background could possibly learn computer science. Programming
was considered a skill that the student was to master on his or her own,
perhaps withinalaboratorysetting. In 1976the IEEE issuedguidelines for
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Preface
afour-yearprogram in ComputerEngineering. Againprogrammingwas not
a task to be lllastered in its own right.
In 1978the ACM revised its curriculum. Forthe firsttime, programming
was mentioned as a topic ofstudy. Another major change was that mathe
matics was considered a co-requisite, rather than a prerequisite, of the
study ofcomputing.
Three things happened in 1983-1984 which solidified the trends in
computer-related education: the ACM approved the revision ofCS1 (Cur
riculum '78) and presented a first draft ofCS2, the IEEE revised its entire
curricululn, and the curriculum for an Advanced Placement Exam in Com
puter Sciences was specified by the College Boards. The correlation be
tween the ACM CS1 and (draft) CS2 and the AP curriculum was extraordi
narily high, and this intersection mapped quite closely onto SubjectAreas
1, 2, and 4 ofthe IEEE curricululn.
Aconsensus has evolved concerning what the curriculum should be for
the first yearofacomputerscience education-withinengineeringorelse
where. To computereducators this is an excitingdevelopment. Pascal Plus
Data Structures, Algorithms, and Advanced Programming covers the ad
vanced topics in this consensus. It is designed to follow a one-semester
course that is an introduction, or its equivalent, to top-down design and
structured programming with Pascal.
WHY THIS TEXT IS D~ffIERENT
Our presentation is unique in that we stress the leading edge ofcomputer
science theory and software engineering principles. These principles in
clude modularization, dataencapsulation, informationhiding, dataabstrac
tion, top-down design ofalgorithms and data structures in parallel, testing
strategies, program verification, and proper documentation.
We feel strongly that these principles can be stressed without resolting
to conlplicatedlnathelnaticalnotation. Therefore,this bookassumes nocol
lege-level mathematics. Even algorithln analysis and program verification
areapproached intuitively. Thosestudents with amathematics background
can understand Engish presentations; those students with no mathematics
cannotunderstandformalisms. We intendto reach both groups ofstudents.
ORGANIZATION AND CONTIENT
Chapter 1 reviews the basic principles of designing computer programs.
We assume that the reader has a basic knowledge ofPascal programming.
The goals for writing a good program are enumerated, and a number of
tools for attaining these goals are described in detail. The techniques for
the top-down design of both programs and data structures are reviewed
with an elnphasis on modularization and good documentation. Approaches
for debugging and testillg are also discussed. Detailed sample problems
illustrate these points.
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Preface
Chapter 2 describes how data structures will be studied throughout the
rest ofthe book. One-diInensional arrays, two-dimensional arrays, and rec
ords-three structured datatypes with which the students shouldbe famil
iarfrom theirfirst course-are examinedfrom three perspectives: the logi
cal level, the application or usage level, and the implementation level.
The concept ofan abstract data type is illustrated in an application that
uses the one-dimensional array and the record to create a string data type.
Utility routines to manipulate the string data type are designed, written,
and tested. The string data type defined here is used in some ofthe appli
cations in later chapters, illustrating the point that once a programmer has
created a user-defined data type, subsequent problems may assume this
type to be "built-in."
In Chapter 3 stacks are introduced to demonstrate the concept ofdata
encapsulation in user-defined data structures. We develop, first, an under
standing of the logical properties and operations on the structure (e.g.,
PUSHand POP), andsecond, one ormore implementations ofthe structure
and its operations in the Pascal programming language. Finally, stacks are
used in two complete programs to illustrate the real-world application of
this data structure.
Queues are discussed in a similarfashion in Chapter4. In addition, this
chapterexamines in detail whatdesign considerations mustbe given to the
choice ofa particular in1plementation. The chapter concludes with an ap
plication that illustrates a queueing system in a simulation problem.
Linked lists are presented in Chapters 5 and 6. The implementation
level inChapter5uses an arrayofrecords; in Chapter6the dynamicimple
mentation oflinked lists is discussed. We decided to present first the idea
oflinkingthe elements in a listinterms ofstructures thatare alreadyfamil
iar (an array ofrecords) before the introduction ofa new, language-depen
dentsyntax.Aftertheconceptsandthisgeneralsolutionarefullyunderstood
in Chapter 5, the syntax ofthe Pascal pointertype is presented in detail in
Chapter 6, along with a discussion ofdynamic allocation. To illustrate its
use, the linked list structure is implemented again using pointervariables.
Doubly-linked lists, circular lists, and lists with headers and trailers are
also discussed.
We present recursion in Chapter7 with two goals for the student-first,
to give him or her an intuitive understanding ofthe concept and a belief
that recursion actually works; and second, to convey how recursion can be
used to solve programming problems. Guidelines for writing recursive
functions andprocedures are illustratedwith many examples, anda simple
technique for verifying the correctness ofa recursive routine is presented.
Since many students are wary of recursion (after having been warned to
avoid its unintentional use in their first course), the presentation here is
deliberately intuitive and nonmathematical.
InChapter8the binarysearchtree is introducedas awayto arrange data
that gives the flexibility ofa linked structure withollt the liability ofslow,
sequential access. The insertion and deletion algorithms are developed in
detail and implemented for a tree whose nodes are linked with pointer
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Preface
variables. A nonrecursive tree traversal is presented usinga stack as a sup
plementary data structure. Then recursive tree traversals are presented,
illustrating how recursion can greatly simplify some programming prob
lems.
Chapter9is a collection ofloosely related topics. We discuss expression
trees, and point out the relationship between the different tree traversals
and mathematical notation. The use ofarrays to implement binary trees is
presented as a lead-in to the discussion ofheaps and heapsort. The final
topic in the chapter is an introduction to graphs.
Chapter10is an introductionto programverification. This topic is onthe
leading edge of theoretical computer science. This is written as a stand
alone chapter, and may be omitted without losing continuity. However,
program verification techniques will be employed by the next generation
ofcomputer professionals to produce reliable software. This chapter is in
tended to introduce students to a topic that they will encounter again in
later courses.
Chapter 11 presents a number ofsorting algorithms and asks the ques
tion: Which is best? To answer this question, we introduce the analysis of
algorithms; and we compare the selection sort, bubble sort, quicksort, and
heapsort. Chapter 12 continues the discussion ofalgorithm analysis in the
context ofsearching. Various searching algorithms are presented and ana
lyzed, including sequential and binary searches and hashing techniques.
In both chapters the practical considerations in choosing appropriate sort
ing and searchingtechniques are balanced by the theoretical concepts be
hind the idea ofmeasuring work.
Chapter 13 is a summary chapter that ties together the ideas introduced
in this book in a discussion ofthe "real-world" programmingenvironment.
The concepts and techniques discussed throughout the previous chapters
are developed to create the principles of software engineering practices
thatare in use todayfor solvinglarge and complex programmingproblems.
ADD~l~ONAL fEATURES
ChapterGoals: Atthe beginningofeach chapterthe goals ofthatchap
terare presented. These goals are then tested in the exercises and pretests
at the end ofthe chapter.
ChapterExercises: Attheendofeachchapter(exceptChapter 13),there
is asetofpaper-and-pencilexercises totestwhetherthe chaptergoals have
been attained. The complete exercise answers are in the back ofthe book.
ChapterPretests: Atthe endofeachchapter(exceptChapter13)there is
a test for the student to measure his or her own progress. The answers to
these questions are in the Instructor's Guide.