Programming with Turing and Object Oriented Turing

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1 Programming with Turing and Object Oriented Turing

2 Peter Grogono Programming with Turing and Object Oriented Turing Springer-Verlag New York Berlin Heidelberg London Paris Tokyo Hong Kong Barcelona Budapest

3 Peter Grogono Department of Computer Science Concordia University Montreal, Quebec H3G 1MB Canada Cover Image Q1995 Michael Schimpf/Panoramic Images, Chicago, All Rights Reserved Windows is a registered trademark of Microsoft Corporation. UNIX is a registered trademark of AT&T. The term "PC" refers to all members of the IBM-PC family and also to compatible clones. The term "Macintosh" refers to all members of the Macintosh family of computers manufactured by Apple. Library of Congress Cataloging-in-Publication Data Grogono, Peter. Programming with Turing and Object Oriented Turing / Peter Grogono p. em. Includes bibliographical references and index. Additional material to this book can be downloaded from ISBN 13: 978 ()' (l 1. Object-oriented programming (Computer science) 2. Turing (Computer program language) 3. Windows (Computer programs) I. Title. QA G '3 --dc20 Printed on acid-free paper. Q 1995 Springer-Verlag New York, Inc. All rights reserved. This work may not be translated or copied in whole or in part without the written pennission of the publisher (Springer-Verlag New York, Inc., 175 Fifth Avenue, New York, NY 10010, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any fonn of infonnation storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use of general descriptive names, trade names, trademarks, etc., in this publication, even if the fonner are not especially identified, is not to be taken as a sign that such names, as under stood by the Trade Marks and Merchandise Marks Act, may accordingly be used freely by anyone. Production managed by Laura Carlson; manufacturing supervised by Joe Quatela. Edited by Sharon H. Nelson, Metonymy Productions. Photocomposed from text prepared by Metonymy Productions using T~ and LATVC. Printed and bound by Hamilton Printing Co., Rensselaer, NY ISBN-1 3: e-isbn- IJ: DOl: /

4 Preface The programming language Thring is Damed for the British mathematician and computer scientist Alan Mathison 'luring ( ). Thring's contributions to computer science began in 1936, when he published a landmark paper on the limits of mechanical computation. The mathematical model introduced in the paper is now known as a unuing machine" and forms the basis of the modern theory of computability. During World War II, Thring played an important role in the design of the Colossus, an electronic machine that deciphered. coded messages. In 1951, he proposed a test, now called the Thring test, to answer the question: Can a machine think? Today, the most distinguished award given by the world's largest association for computing professionals, the Association for Computing Machinery, is called the Thring Award. The programming language Thring was designed by Richard C. Holt and James R. Cordy at the University of Toronto as a first language for computer science courses. Thring is a practical language suited to general-purpose applications. Like the work of the person for whom it is named, the language Thring serves well in both the theoretical and practical domains. Most of the software that supports Thring, including the Turing compiler, is written in Turing. This book includes all the features of Thring and provides an introduction to the object oriented features of the more recent language, Object Oriented Thring (OOT).

vi Preface Thring is particularly appropriate as a first language for learning and teaching. It incorporates many of the advantages while avoiding most of the disadvantages of earlier languages.

5 vi Preface Thring is particularly appropriate as a first language for learning and teaching. It incorporates many of the advantages while avoiding most of the disadvantages of earlier languages. The following four features make Thring particularly suitable as a first language and as a pedagogical tool. Turing is learned in easy stages. As a first step, we can write one-line programs in Turing. We can continue by writing programs of increasing complexity, adding one or two new features at a time. This distinguishes Thring from languages that require knowledge of advanced programming concepts before even simple programs can be written. Turing is defined by simple rules with few exceptions. With a little effort, it is easy to learn the entire language. This distinguishes Thring from languages that breed gurus and wizards who revel in arcane and obscure features. Turing is a standardized language. Most Thring programs written on a PC will run on a Macintosh or a UNIX workstation and give the same results. Only a few features of Thring, such as graphics, do not work in the same way on all systems. This distinguishes Thring from languages that require programs to be adapted for different systems. Thring has a formal definition and semantics. This distinguishes Thring from languages defined by a lengthy, complex, and potentially ambiguous report written in a natural language. Effective programming requires capabilities in four separate but related areas. First, we achieve the capability to write programs in a particular language. This requires knowledge of the syntax, semantics, and style of the language. Second, we learn how to choose control and data structures that are appropriate for each problem and to demonstrate that they do in fact solve the problem correctly. Although the techniques vary from one language paradigm to another, this capability is largely independent of any particular language. Third, because most programming problems can be solved using techniques that are well understood and widely documented, we acquire a repertoire of standard algorithms and data structures. Fourth, because new problems arise, we learn to design new algorithms and data structures. Programming with Turing focuses on the capabilities of writing programs and of choosing appropriate control and data structures. A book that teaches a programming language ideally satisfies two requirements. It provides a narrative that reveals successively more advanced features of the language and a reference source in which particular features of the language can be found quickly. Each section of Programming with Turing is constructed to make use of the material and examples presented in previous sections. Each chapter ends with a collection of exercises intended to develop confidence and

6 Preface vii familiarity with Turing and with general principles of programming. At the same time, Programming with Thring is organized to serve as a reference source: each section covers a specific topic; each chapter includes summaries; and appendices offer quick reference for particular features. Many of the examples and exercises are about hobbies, physics, and other areas of application. They show some of the ways in which the ability to understand and use basic computational skills can enrich our lives. In addition, they offer a sample of programming tasks and of what programming is about. I could not have written Programming with Thring without the Turing software and technical assistance provided by Ric Holt and Chris Stephenson at Holt Software Associates. I am grateful to Sharon H. Nelson at Metonymy Productions for detailed and thorough editing. January 1995 P.G. Montreal How to Install the Software Appendix K, on page 375, explains how to install WinOOT from the disk included with this book. Appendix L, on page 376, explains how to run WinOOT. Before installing WinOOT, you should ensure that at le8bt 2 megabytes of virtual memory are available to Windows

7 Contents Preface 1 First Concepts 1.1 Writing Simple Programs 1.2 Learning to Read Programs introduction to Standard Types Declarations Output and Input 1.6 Comments Summary 1.8 Exercises.. 2 Assignment and Control 2.1 The Assignment Statement 2.2 Sequences Decisions Repetition Scopes and Local Declarations... v

8 x Contents 2.6 The Form and Content of Statements Summary Exercises Standard Types and Expressions The Role of Types in Programs The Types int and real The Type boolean The Type string Type Conversion Summary Exercises Defining New Types Subranges Enumerations Arrays Summary Exercises Procedures and Functions Predefined Procedures and Functions Declaring New Procedures New Functions Recursive Subprograms Rules for Subprograms Preconditions and Postconditions Summary Exercises Input and Output Managing the Keyboard Managing the Screen Text Files

9 Contents x; 6.4 Summary 6.5 Exercises 7 Sound and Graphics 7.1 Sound Graphics Animation. 7.4 Summary 7.5 Exercises 8 Sets, Records, and Unions 8.1 Sets Reco"ls 8.3 Unions. 8.4 The bind Statement 8.5 Summary 8.6 Exercises 9 Collections 9.1 From Arrays to Collections 9.2 Linked Lists The new and free Statements 9.4 Collections and Recursion Designing a Symbolic Calculator 9.6 Summary 9.7 Exercises 10 Organizing Large Programs 10.1 Modules The include Directive Summary 10.4 Exercises

10 xii Contents 11 Additional Features 11.1 Binary Files Subprogram Arguments 11.3 Summary 11.4 Exercises Object Oriented. 'luring 12.1 Classes and Objects 12.2 Inheritance Frameworks Ancestors and Descendants 12.5 Summary 12.6 Exercises Appendixes A B C D E F G H I J K L Index 'luring Keywords Expression Operators Assignment Operators Predefined Functions and Procedures. Codes for the ASCII Graphic Character Set ASCII Codes for Border Characters Values Returned by getch The Procedure play..... The Procedure setscreen Colors for the mm PC and Compatibles. Installing WinOOT. Running WinOOT

11 List of Figures 1.1 Evaluation of Numeric Operators Comparison Operators and Their Meanings Using the get Statement to Read Strings Abbreviated Assignments Tax Rates in Thringia Nested Scopes Operator Precedence Expressions and Their Types Properties of the Exponent Operator Predefined Numeric FUnctions Truth Table for Boolean Operators Using "\ " in Strings Conversion Functions and put Statements A Real Variable, Average, and an Array, Scores Plotting a Random Distribution

12 xiv List of Figures 5.2 Dividing the Line Procedures for Measuring and Displaying Time 5.4 The Odometer of a Car The Coordinate System for Pixel Graphics. 7.2 Coordinate Systems for Scaling Transformation 7.3 Conventions for Angles Using takepic and drawpic Set Operations and Predicates 8.2 Properties of Food Displaying a Bridge Hand A Value of the Type RoseRecord 9.1 Declaring a Pointer Variable Allocating Memory for the String. 9.3 Storing a String in a Collection Two Pointers to the Same Component 9.5 Copying Pointers and Copying Components 9.6 A Linked List The First Two Components Adding a New Component to a Linked List 9.9 A Dangling Pointer A Binary Search Tree Representing a State of the Calculator 9.12 Scanning the Input 11.1 File Position Pumping Numbers and Filtering Primes 12.2 Operations for a Graphics Program Adding a Method to the Graphics Program 12.4 Adding a Class to the Graphics Program A Program Using Components from a Library A Program Using a Framework from a Library 12.7 The Model-View-Controller Framework

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