Jim Welsh and John Elder Introduction to Modula-2 PRENTICE HALL INTERNATIONAL SERIES IN COMPUTER SCIENCE C.A.R. HOARE SERIES EDITOR INTRODUCTION TO MODULA-2 Prentice Hall International Series in Computer Science C. A. R. Hoare, Series Editor BACKHOUSE, R. C., Program Construction and Verification BACKHOUSE, R. C., Syntax ofProgramming Languages, Theory and Practice de BAKKER, J. W., Mathematical Theory ofProgram Correctness BJORNER, D., and JONES, C. B., Formal Specification and Software Development BORNAT, R., Programmingfrom First Principles CLARK, K. L., and McCABE, F. G., micro-PROLOG: Programming in Logic DROMEY, R. G., How to Solve it by Computer DUNCAN, F., Microprocessor Programming and Software Development ELDER, J., Construction ofData Processing Software GOLDSCHLAGER, L., and LISTER, A., Computer Science: A Modern Introduction HAYES, I. (Editor), Specification Case Studies HEHNER, E. C. R., The Logic ofProgramming HENDERSON, P., Funct,onal Programming: Application and Implementation HOARE, C. A. R., Communicating Sequential Processes HOARE, C. A. R., and SHEPHERDSON, J. C. (Editors), Mathematical Logic and Programming Languages INMOS LTD, Occam Programming Manual JACKSON, M. A., System Development JOHNSTON, H., Learning to Program JONES, C. B.,Systematic Software Development Using VDM JONES, G., Programming in Occam JOSEPH, M., PRASAD, V. R.,and NATARAJAN, N.,A Multiprocessor Operating System LEW, A., Computer Science: A Mathematical Introduction MacCALLUM, I., Pascalfor the Apple MacCALLUM, I., UCSD Pascalfor the IBM PC MARTIN, J. J., Data Types and Data Structures POMBERGER, G., Software Engineering and Modula-2 REYNOLDS, J. C., The CraftofProgramming SLOMAN, M., and KRAMER, J., Distributed Systems and Computer Networks TENNENT, R. D., Principles ofProgramming Languages WELSH, J., and ELDER, J., Introduction to Modula-2 WELSH, J., and ELDER, J., Introduction to Pascal, 2nd Edition WELSH, J., ELDER, J., and BUSTARD, D., Sequential Program Structures WELSH, J., and HAY, A.,A Model Implementation ofStandard Pascal WELSH, J., and McKEAG, M.. Structured System Programming INTRODUCTION TO MODULA-2 JIM WELSH University of Queensland, Australia JOHN ELDER Queen's University of Belfast, Northern Ireland PRENTICE HALL NewYork London Sydney Tokyo Welsh, Jim, 1943- Introduction to Modula-2. (Prentice Hall International Series in Computer Science) Includes index. 1. Modula-2 (Computer program language) I. Elder, John, 1949— . 11. Title. III. Title: Introduction to Modula-Two. IV. Series. QA76.73.M63W45 1987 005.13'3 87-11521 ISBN 0-13-488610-0 (pbk.) British Library Cataloguing in Publication Data Welsh, Jim Introduction to Modula-2.—(Prentice Hall International Series in Computer Science). 1. Modula-2 (Computer program language) I. Title II. Elder, John, 1949 - 005.13'3 QA76.73.M63 ISBN 0-13-488610-0 © 1987 Prentice Hall International (UK) Ltd All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of Prentice Hall International (UK) Ltd. For permission within the United States of America contact Prentice Hall Inc., Englewood Cliffs, NJ 07632. Prentice Hall is an imprint of the Simon & Schuster International Group. Printed and bound in Great Britain for Simon & Schuster International Group, 66 Wood Lane End, Hemel Hempstead, Hertfordshire, HP2 4RG by A. Wheaton and Company Limited, Exeter 1 2345 91 90 89 88 87 0-l'3-4flflblQ-D Contents PREFACE, XI CHAPTER 1 COMPUTERS AND PROGRAMMESG, 1 • The computer, 1 •Writing a computer program, 3 • Running a computer program, 4 • Language implementations, 6 • Programming objectives, 6 • Correctness, 6 • Clarity, 7 • Efficiency, 8 CHAPTER 2 NOTATIONS AND BASIC CONCEPTS, 9 • Which Modula-2?, 9 • Extended Backus-Naur form, 10 • The vocabulary of Modula-2,12 • Numbers, 13 • Identifiers, 14 • Strings, 16 • Comments, 17 • Basic program structure, 18 • Exercises, 21 CHAPTER 3 DATA TYPES AND DECLARATIONS, 22 • Data types, 22 • The type INTEGER, 23 • The type CARDINAL, 25 •The typeLONGDNT, 25 • The type REAL, 26 • The type CHAR, 27 • The type BOOLEAN, 29 • Enumerated types, 31 • Subrange types, 32 • Data declarations, 34 • Constants and constant declarations, 34 • Type declarations, 35 • Variable declarations, 37 • Uniqueness and order of declarations, 38 • Exercises, 39 CHAPTER 4 STATEMENTS, EXPRESSIONS AND ASSIGNMENTS, 41 • Statements,41 • Expressions, 42 • The assignment statement, 46 • Exercises, 49 CHAPTER 5 INPUT AND OUTPUT OF DATA, 51 • Transferring data to and firom the program, 51 • Output from Modula-2 programs, 52 • Input to Modula-2 programs, 55 • Import-lists, 58 • Case study 1,59 • Alternative input and output streams, 63 • Exercises, 65 CHAPTER 6 BASIC CONTROL STRUCTURES, 66 • Statement sequences, 66 • Conditional statements, 68 • The if-statement, 68 • Case study 2,72 • The case-statement, 74 • Case study 3,77 • Repetitive statements, 80 • The while-statement, 81 • The repeat-statement, 83 • The for-statement, 84 • Nested loops, 88 • Case study 4, 89 • The loop-statement, 93 • Exercises, 97