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Chapter 10 Class Scope, Public and Private Members, p. 565 Default Initialization of Member Variables, p. 587 Separate Interface and Implementation, p. 592 Solution to Practice Program 10.1, p. 611
Chapter 11 const Confusion, p. 639 Arrays of Classes using Dynamic Arrays, p. 671 Overloading = and == for a Class, p. 680 Solution to Programming Project 11.12, p. 701
Chapter 12 Avoiding Multiple Definitions, p. 715 Solution to Practice Program 12.3, p. 736
Chapter 13 Walkthrough of Linked Lists of Classes, p. 762 Solution to Programming Project 13.6, p. 783 Solution to Programming Project 13.9, p. 785
Chapter 14 Recursion and the Stack, p. 801 Solution to Practice Program 14.4, p. 827 Solution to Practice Program 14.4 , p. 828
Chapter 15 Inheritance Example, p. 858 Solution to Practice Program 15.3, p. 882 Solution to Programming Project 15.1, p. 884 Solution to Programming Project 15.10, p. 889
Chapter 16 The STL Exception Class, p. 917 Solution to Practice Program 16.1, p. 920 Solution to Programming Project 16.3, p. 922
Chapter 17 Issues Compiling Programs with Templates, p. 931 Solution to Programming Project 17.7, p. 955
Chapter 18 C++11 and Containers, p. 990 Solution to Practice Program 18.2, p. 1007 Solution to Programming Project 18.6, p. 1010
(Continued from Inside Front Cover)
Problem Solving with C++ ninth edition
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Problem Solving with C++
Walter Savitch University of California, san Diego
Contributor
Kenrick mock University of alaska, anChorage
ninth edition
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Library of Congress Cataloging-in-Publication Data
Savitch, Walter J., 1943- Problem solving with C++ / Walter Savitch ; contributor, Kenrick Mock. -- Ninth edition. pages cm Includes index. ISBN-13: 978-0-13-359174-3 (alkaline paper) ISBN-10: 0-13-359174-3 (alkaline paper) 1. C++ (Computer program language) 2. Problem solving. I. Mock, Kenrick. II. Title. QA76.73.C153S29 2014 005.13'3--dc23 2013048487
10 9 8 7 6 5 4 3 2 1—CW—15 14 13 12 11 ISBN 10: 0-13-359174-3 www.pearsonhighered.com ISBN 13: 978-0-13-359174-3
www.pearsonhighered.com
v
Preface
This book is meant to be used in a first course in programming and computer science using the C++ language. It assumes no previous programming experi- ence and no mathematics beyond high school algebra.
If you have used the previous edition of this book, you should read the following section that explains the changes to this ninth edition and then you can skip the rest of this preface. If you are new to this book, the rest of this preface will give you an overview of the book.
Changes to the Ninth Edition This ninth edition presents the same programming philosophy as the eighth edition. All of the material from the eighth edition remains, but with the fol- lowing enhancements:
■ End-of-chapter programs are now split into Practice Programs and Program- ming Projects. Practice Programs require a direct application of concepts presented in the chapter and solutions are usually short. Practice Programs are appropriate for laboratory exercises. Programming Projects require ad- ditional problem solving and solutions are generally longer than Practice Programs. Programming Projects are appropriate for homework problems.
■ Introduction to C++11 in the context of C++98. Examples of C++11 content includes new integer types, the auto type, raw string literals, strong enumera- tions, nullptr, ranged for loop, conversion between strings and integers, member initializers, and constructor delegation.
■ Additional material on sorting, secure programming (e.g., overflow, array out of bounds), and inheritance.
■ Correction of errata. ■ Twenty-one new Practice Programs and ten new Programming Projects. ■ Ten new VideoNotes for a total of sixty-four VideoNotes. These VideoNotes
walk students through the process of both problem solving and coding to help reinforce key programming concepts. An icon appears in the margin of the book when a VideoNote is available regarding the topic covered in the text.
If you are an instructor already using the eighth edition, you can continue to teach your course almost without change.
Flexibility in Topic Ordering This book was written to allow instructors wide latitude in reordering the material. To illustrate this flexibility, we suggest two alternative ways to order
vi Preface
the topics. There is no loss of continuity when the book is read in either of these ways. To ensure this continuity when you rearrange material, you may need to move sections rather than entire chapters. However, only large sec- tions in convenient locations are moved. To help customize a particular order for any class’s needs, the end of this preface contains a dependency chart, and each chapter has a “Prerequisites” section that explains what material needs to be covered before each section in that chapter.
Reordering 1: Earlier Classes
To effectively design classes, a student needs some basic tools such as control structures and function definitions. This basic material is covered in Chapters 1 through 6. After completing Chapter 6, students can begin to write their own classes. One possible reordering of chapters that allows for such early coverage of classes is the following:
Basics: Chapters 1, 2, 3, 4, 5, and 6. This material covers all control struc- tures, function definitions, and basic file I/O. Chapter 3, which covers ad- ditional control structures, could be deferred if you wish to cover classes as early as possible.
Classes and namespaces: Chapter 10, Sections 11.1 and 11.2 of Chapter 11, and Chapter 12. This material covers defining classes, friends, overloaded operators, and namespaces.
Arrays, strings and vectors: Chapters 7 and 8
Pointers and dynamic arrays: Chapter 9
Arrays in classes: Sections 11.3 and 11.4 of Chapter 11
Inheritance: Chapter 15
Recursion: Chapter 14 (Alternately, recursion may be moved to later in the course.)
Pointers and linked lists: Chapter 13
Any subset of the following chapters may also be used:
Exception handling: Chapter 16
Templates: Chapter 17
Standard Template Library: Chapter 18
Reordering 2: Classes Slightly Later but Still Early
This version covers all control structures and the basic material on arrays be- fore doing classes, but classes are covered later than the previous ordering and slightly earlier than the default ordering.
Basics: Chapters 1, 2, 3, 4, 5, and 6. This material covers all control struc- tures, function definitions, and the basic file I/O.
Preface vii
Arrays and strings: Chapter 7, Sections 8.1 and 8.2 of Chapter 8
Classes and namespaces: Chapter 10, Sections 11.1 and 11.2 of Chapter 11, and Chapter 12. This material covers defining classes, friends, overloaded operators, and namespaces.
Pointers and dynamic arrays: Chapter 9
Arrays in classes: Sections 11.3 and 11.4 of Chapter 11
Inheritance: Chapter 15
Recursion: Chapter 14. (Alternately, recursion may be moved to later in the course.)
Vectors: Chapter 8.3
Pointers and linked lists: Chapter 13
Any subset of the following chapters may also be used:
Exception handling: Chapter 16
Templates: Chapter 17
Standard Template Library: Chapter 18
Accessibility to Students
It is not enough for a book to present the right topics in the right order. It is not even enough for it to be clear and correct when read by an instructor or other experienced programmer. The material needs to be presented in a way that is accessible to beginning students. In this introductory textbook, I have endeav- ored to write in a way that students find clear and friendly. Reports from the many students who have used the earlier editions of this book confirm that this style makes the material clear and often even enjoyable to students.
ANSI/ISO C++ Standard
This edition is fully compatible with compilers that meet the latest ANSI/ISO C++ standard. At the time of this writing the latest standard is C++11.
Advanced Topics
Many “advanced topics” are becoming part of a standard CS1 course. Even if they are not part of a course, it is good to have them available in the text as enrichment material. This book offers a number of advanced topics that can be integrated into a course or left as enrichment topics. It gives thorough cov- erage of C++ templates, inheritance (including virtual functions), exception handling, and the STL (Standard Template Library). Although this book uses libraries and teaches students the importance of libraries, it does not require any nonstandard libraries. This book uses only libraries that are provided with essentially all C++ implementations.
viii Preface
Dependency Chart
The dependency chart on the next page shows possible orderings of chapters and subsections. A line joining two boxes means that the upper box must be covered before the lower box. Any ordering that is consistent with this partial ordering can be read without loss of continuity. If a box contains a section number or numbers, then the box refers only to those sections and not to the entire chapter.
Summary Boxes
Each major point is summarized in a boxed section. These boxed sections are spread throughout each chapter.
Self-Test Exercises
Each chapter contains numerous Self-Test Exercises at strategic points. Com- plete answers for all the Self-Test Exercises are given at the end of each chapter.
VideoNotes
VideoNotes are designed for teaching students key programming concepts and techniques. These short step-by-step videos demonstrate how to solve problems from design through coding. VideoNotes allow for self-paced instruction with easy navigation including the ability to select, play, rewind, fast-forward, and stop within each VideoNote exercise.
Online Practice and Assessment with MyProgrammingLab
MyProgrammingLab helps students fully grasp the logic, semantics, and syn- tax of programming. Through practice exercises and immediate, personalized feedback, MyProgrammingLab improves the programming competence of be- ginning students who often struggle with the basic concepts and paradigms of popular high-level programming languages.
A self-study and homework tool, a MyProgrammingLab course consists of hundreds of small practice problems organized around the structure of this textbook. For students, the system automatically detects errors in the logic and syntax of their code submissions and offers targeted hints that enable students to figure out what went wrong—and why. For instructors, a comprehensive gradebook tracks correct and incorrect answers and stores the code inputted by students for review.
MyProgrammingLab is offered to users of this book in partnership with Turing’s Craft, the makers of the CodeLab interactive programming exer- cise system. For a full demonstration, to see feedback from instructors and students, or to get started using MyProgrammingLab in your course, visit www.myprogramminglab.com.
VideoNote
www.myprogramminglab.com
Preface ix
DISPLAY P.1 Dependency Chart
*Chapter 16 contains occasional references to derived classes, but those references can be omitted
Chapter 1 Introduction
Chapter 2 C++ Basics
Chapter 3 More Flow of Control
Chapter 6 I/O Streams
Chapter 7 Arrays 7.1–7.3
Chapter 14 Recursion
Chapter 10 Classes 1
Chapter 11 Classes 2 11.1–11.2
Chapter 7 7.4 Multi-
Dimensional Arrays
Chapter 15 Inheritance
*Chapter 16 Exception Handling
Chapter 12 Separate
Compilation & Namespaces
Chapter 11 11.3 Classes &
Arrays
Chapter 11 11.4 Classes &
Dynamic Arrays
Chapter 17 Templates
Chapter 18 STL
Chapter 9 Pointers and
Dynamic Arrays
Chapter 8 Strings and
Vectors
Chapter 13 Pointers and Linked Lists
Chapter 4 Functions 1
Chapter 5 Functions 2
x Preface
Support Material
There is support material available to all users of this book and additional material available only to qualified instructors.
Materials Available to All Users of this Book
■ Source Code from the book ■ PowerPoint slides ■ VideoNotes
To access these materials, go to: www.pearsonhighered.com/savitch
Resources Available to Qualified Instructors Only
Visit Pearson Education’s instructor resource center at www.pearsonhighered .com/irc to access the following instructor resources:
■ Instructor’s Resource Guide—including chapter-by-chapter teaching hints, quiz questions with solutions, and solutions to many programming projects
■ Test Bank and Test Generator ■ PowerPoint Lectures—including programs and art from the text ■ Lab Manual
Integrated Development Environment (IDE) Resource Kits
Instructors who adopt this text can order it for students with a kit containing five popular C++ IDEs (Microsoft® Visual Studio 2013 Express Edition, Dev C++, NetBeans, Eclipse, and CodeLite) and access to a Web site containing written and video tutorials for getting started in each IDE. For ordering infor- mation, please contact your campus Pearson Education representative.
Contact Us
Your comments, suggestions, questions, and corrections are always welcome. Please e-mail them to savitch.programming.cpp@gmail.com
Acknowledgments
Numerous individuals and groups have provided me with suggestions, discus- sions, and other help in preparing this textbook. Much of the first edition of this book was written while I was visiting the Computer Science Department at the University of Colorado in Boulder. The remainder of the writing on the first edition and the work on subsequent editions was done in the Computer Science and Engineering Department at the University of California, San Diego (UCSD). I am grateful to these institutions for providing a conducive environ- ment for teaching this material and writing this book.
www.pearsonhighered.com/savitch
www.pearsonhighered.com/irc
www.pearsonhighered.com/irc
Preface xi
I extend a special thanks to all the individuals who have contributed critiques or programming projects for this or earlier editions and drafts of this book. In alphabetical order, they are: Alex Feldman, Amber Settle, Andrew Burt, Andrew Haas, Anne Marchant, Barney MacCabe, Bob Holloway, Bob Matthews, Brian R. King, Bruce Johnston, Carol Roberts, Charles Dowling, Claire Bono, Cynthia Martincic, David Feinstein, David Teague, Dennis Heckman, Donald Needham, Doug Cosman, Dung Nguyen, Edward Carr, Eitan M. Gurari, Ethan Munson, Firooz Khosraviyani, Frank Moore, Gilliean Lee, Huzefa Kagdi, James Stepleton, Jeff Roach, Jeffrey Watson, Jennifer Perkins, Jerry Weltman, Joe Faletti, Joel Cohen, John J. Westman, John Marsaglia, John Russo, Joseph Allen, Joseph D. Oldham, Jerrold Grossman, Jesse Morehouse, Karla Chaveau, Ken Rockwood, Larry Johnson, Len Garrett, Linda F. Wilson, Mal Gunasekera, Marianne Lepp, Matt Johnson, Michael Keenan, Michael Main, Michal Sramka, Naomi Shapiro, Nat Martin, Noah Aydin, Nisar Hundewale, Paul J. Kaiser, Paul Kube, Paulo Franca, Richard Borie, Scot Drysdale, Scott Strong, Sheila Foster, Steve Mahaney, Susanne Sherba, Thomas Judson, Walter A. Manrique, Wei Lian Chen, and Wojciech Komornicki.
I extend a special thanks to the many instructors who used early editions of this book. Their comments provided some of the most helpful reviewing that the book received.
Finally, I thank Kenrick Mock who implemented the changes in this edition. He had the almost impossible task of pleasing me, my editor, and his own sensibilities, and he did a superb job of it.
Walter Savitch
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Through the power of practice and immediate personalized
feedback, MyProgrammingLab improves your performance.
Learn more at www.myprogramminglab.com
get with the programming
To improving results
www.myprogramminglab.com
xiv
Brief Contents
Table of Location of VideoNotes Inside front cover and inside back cover
Chapter 1 Introduction to Computers and C++ Programming 1
Chapter 2 C++ Basics 39
Chapter 3 More Flow of Control 111
Chapter 4 Procedural Abstraction and Functions That Return a Value 181
Chapter 5 Functions for All Subtasks 251
Chapter 6 I/O Streams as an Introduction to Objects and Classes 305
Chapter 7 Arrays 377
Chapter 8 Strings and Vectors 451
Chapter 9 Pointers and Dynamic Arrays 507
Chapter 10 Defining Classes 541
Chapter 11 Friends, Overloaded Operators, and Arrays in Classes 619
Brief contents xv
Chapter 12 Separate Compilation and Namespaces 703
Chapter 13 Pointers and Linked Lists 739
Chapter 14 Recursion 789
Chapter 15 Inheritance 833
Chapter 16 Exception Handling 893
Chapter 17 Templates 925
Chapter 18 Standard Template Library 957
Appendices 1 C++ Keywords 1015 2 Precedence of Operators 1016 3 The ASCII Character Set 1018 4 Some Library Functions 1019 5 Inline Functions 1026 6 Overloading the Array Index
Square Brackets 1027
7 The this Pointer 1029 8 Overloading Operators as Member
Operators 1032
Index 1034
xvi
Contents
Table of Location of VideoNotes Inside front cover and inside back cover
Chapter 1 Introduction to Computers and C++ Programming 1
1.1 COMPuTER SYSTEMS 2
Hardware 2
Software 7
High-Level Languages 8
Compilers 9
History Note 12
1.2 PROgRAMMINg AND PROBLEM-SOLVINg 12
Algorithms 12
Program Design 15
Object-Oriented Programming 16
The Software Life Cycle 17
1.3 INTRODuCTION TO C++ 18
Origins of the C++ Language 18
A Sample C++ Program 19
Pitfall: Using the Wrong Slash in \n 23
Programming Tip: Input and Output Syntax 23
Layout of a Simple C++ Program 24
Pitfall: Putting a Space Before the include File Name 26
Compiling and Running a C++ Program 26
Pitfall: Compiling a C++11 program 27
Programming Tip: Getting Your Program to Run 27
1.4 TESTINg AND DEBuggINg 29
Kinds of Program Errors 30
Pitfall: Assuming Your Program Is Correct 31
contents xvii
Chapter Summary 32
Answers to Self-Test Exercises 33
Practice Programs 35
Programming Projects 36
Chapter 2 C++ Basics 39
2.1 VARIABLES AND ASSIgNMENTS 40
Variables 40
Names: Identifiers 42
Variable Declarations 44
Assignment Statements 45
Pitfall: Uninitialized Variables 47
Programming Tip: Use Meaningful Names 49
2.2 INPuT AND OuTPuT 50
Output Using cout 50
Include Directives and Namespaces 52
Escape Sequences 53
Programming Tip: End Each Program with a \n or endl 55
Formatting for Numbers with a Decimal Point 55
Input Using cin 56
Designing Input and Output 58
Programming Tip: Line Breaks in I/O 58
2.3 DATA TYPES AND ExPRESSIONS 60
The Types int and double 60
Other Number Types 62
C++11 Types 63
The Type char 64
The Type bool 66
Introduction to the Class string 66
Type Compatibilities 68
Arithmetic Operators and Expressions 69
Pitfall: Whole Numbers in Division 72
More Assignment Statements 74
2.4 SIMPLE FLOw OF CONTROL 74
A Simple Branching Mechanism 75
Pitfall: Strings of Inequalities 80
Pitfall: Using = in place of == 81
Compound Statements 82
xviii contents
Simple Loop Mechanisms 84
Increment and Decrement Operators 87
Programming Example: Charge Card Balance 89
Pitfall: Infinite Loops 90
2.5 PROgRAM STYLE 93
Indenting 93
Comments 93
Naming Constants 95
Chapter Summary 98
Answers to Self-Test Exercises 98
Practice Programs 103
Programming Projects 105
Chapter 3 More Flow of Control 111
3.1 uSINg BOOLEAN ExPRESSIONS 112
Evaluating Boolean Expressions 112
Pitfall: Boolean Expressions Convert to int Values 116
Enumeration Types (Optional) 119
3.2 MuLTIwAY BRANCHES 120
Nested Statements 120
Programming Tip: Use Braces in Nested Statements 121
Multiway if-else Statements 123
Programming Example: State Income Tax 125
The switch Statement 128
Pitfall: Forgetting a break in a switch Statement 132
Using switch Statements for Menus 133
Blocks 135
Pitfall: Inadvertent Local Variables 138
3.3 MORE ABOuT C++ LOOP STATEMENTS 139
The while Statements Reviewed 139
Increment and Decrement Operators Revisited 141
The for Statement 144
Pitfall: Extra Semicolon in a for Statement 149
What Kind of Loop to Use 150
Pitfall: Uninitialized Variables and Infinite Loops 152
The break Statement 153
Pitfall: The break Statement in Nested Loops 154
contents xix
3.4 DESIgNINg LOOPS 155
Loops for Sums and Products 155
Ending a Loop 157
Nested Loops 160
Debugging Loops 162
Chapter Summary 165
Answers to Self-Test Exercises 166
Practice Programs 172
Programming Projects 174
Chapter 4 Procedural Abstraction and Functions That Return a Value 181
4.1 TOP-DOwN DESIgN 182
4.2 PREDEFINED FuNCTIONS 183
Using Predefined Functions 183
Random Number Generation 188
Type Casting 190
Older Form of Type Casting 192
Pitfall: Integer Division Drops the Fractional Part 192
4.3 PROgRAMMER-DEFINED FuNCTIONS 193
Function Definitions 193
Functions That Return a Boolean Value 199
Alternate Form for Function Declarations 199
Pitfall: Arguments in the Wrong Order 200
Function Definition–Syntax Summary 201
More About Placement of Function Definitions 202
Programming Tip: Use Function Calls in Branching Statements 203
4.4 PROCEDuRAL ABSTRACTION 204
The Black-Box Analogy 204
Programming Tip: Choosing Formal Parameter Names 207
Programming Tip: Nested Loops 208
Case Study: Buying Pizza 211
Programming Tip: Use Pseudocode 217
4.5 SCOPE AND LOCAL VARIABLES 218
The Small Program Analogy 218
Programming Example: Experimental Pea Patch 221
xx contents
Global Constants and Global Variables 221
Call-by-Value Formal Parameters Are Local Variables 224
Block Scope 226
Namespaces Revisited 227
Programming Example: The Factorial Function 230
4.6 OVERLOADINg FuNCTION NAMES 232
Introduction to Overloading 232
Programming Example: Revised Pizza-Buying Program 235
Automatic Type Conversion 238
Chapter Summary 240
Answers to Self-Test Exercises 240
Practice Programs 245
Programming Projects 247
Chapter 5 Functions for All Subtasks 251
5.1 void FuNCTIONS 252
Definitions of void Functions 252
Programming Example: Converting Temperatures 255
return Statements in void Functions 255
5.2 CALL-BY-REFERENCE PARAMETERS 259
A First View of Call-by-Reference 259
Call-by-Reference in Detail 262
Programming Example: The swap_values Function 267
Mixed Parameter Lists 268
Programming Tip: What Kind of Parameter to Use 269
Pitfall: Inadvertent Local Variables 270
5.3 uSINg PROCEDuRAL ABSTRACTION 273
Functions Calling Functions 273
Preconditions and Postconditions 275
Case Study: Supermarket Pricing 276
5.4 TESTINg AND DEBuggINg FuNCTIONS 281
Stubs and Drivers 282
5.5 gENERAL DEBuggINg TECHNIquES 287
Keep an Open Mind 287
Check Common Errors 287
contents xxi
Localize the Error 288
The assert Macro 290
Chapter Summary 292
Answers to Self-Test Exercises 293
Practice Programs 296
Programming Projects 299
Chapter 6 I/O Streams as an Introduction to Objects and Classes 305
6.1 STREAMS AND BASIC FILE I/O 306
Why Use Files for I/O? 307
File I/O 308
Introduction to Classes and Objects 312
Programming Tip: Check Whether a File Was Opened
Successfully 314
Techniques for File I/O 316
Appending to a File (Optional) 320
File Names as Input (Optional) 321
6.2 TOOLS FOR STREAM I/O 323
Formatting Output with Stream Functions 323
Manipulators 329
Streams as Arguments to Functions 332
Programming Tip: Checking for the End of a File 332
A Note on Namespaces 335
Programming Example: Cleaning Up a File Format 336
6.3 CHARACTER I/O 338
The Member Functions get and put 338
The putback Member Function (Optional) 342
Programming Example: Checking Input 343
Pitfall: Unexpected '\n' in Input 345
Programming Example: Another new_line Function 347
Default Arguments for Functions (Optional) 348
The eof Member Function 353
Programming Example: Editing a Text File 355
Predefined Character Functions 356
Pitfall: toupper and tolower Return Values 358
xxii contents
Chapter Summary 360
Answers to Self-Test Exercises 361
Practice Programs 368
Programming Projects 370
Chapter 7 Arrays 377
7.1 INTRODuCTION TO ARRAYS 378
Declaring and Referencing Arrays 378
Programming Tip: Use for Loops with Arrays 380
Pitfall: Array Indexes Always Start with Zero 380
Programming Tip: Use a Defined Constant for the
Size of an Array 380
Arrays in Memory 382
Pitfall: Array Index Out of Range 383
Initializing Arrays 386
Programming Tip: C++11 Range-Based for Statement 386
7.2 ARRAYS IN FuNCTIONS 389
Indexed Variables as Function Arguments 389
Entire Arrays as Function Arguments 391
The const Parameter Modifier 394
Pitfall: Inconsistent Use of const Parameters 397
Functions That Return an Array 397
Case Study: Production Graph 398
7.3 PROgRAMMINg wITH ARRAYS 411
Partially Filled Arrays 411
Programming Tip: Do Not Skimp on Formal Parameters 414
Programming Example: Searching an Array 414
Programming Example: Sorting an Array 417
Programming Example: Bubble Sort 421
7.4 MuLTIDIMENSIONAL ARRAYS 424
Multidimensional Array Basics 425
Multidimensional Array Parameters 425
Programming Example: Two-Dimensional
Grading Program 427
Pitfall: Using Commas Between Array Indexes 431
contents xxiii
Chapter Summary 432
Answers to Self-Test Exercises 433
Practice Programs 437
Programming Projects 439
Chapter 8 Strings and Vectors 451
8.1 AN ARRAY TYPE FOR STRINgS 453
C-String Values and C-String Variables 453
Pitfall: Using = and == with C Strings 456
Other Functions in
Pitfall: Copying past the end of a C-string using strcpy 461
C-String Input and Output 464
C-String-to-Number Conversions and Robust Input 466
8.2 THE STANDARD string CLASS 472
Introduction to the Standard Class string 472
I/O with the Class string 475
Programming Tip: More Versions of getline 478
Pitfall: Mixing cin >> variable; and getline 479
String Processing with the Class string 480
Programming Example: Palindrome Testing 484
Converting Between string Objects and C Strings 487
Converting Between Strings and Numbers 488
8.3 VECTORS 489
Vector Basics 489
Pitfall: Using Square Brackets Beyond the Vector Size 492
Programming Tip: Vector Assignment Is Well Behaved 493
Efficiency Issues 493
Chapter Summary 495
Answers to Self-Test Exercises 495
Practice Programs 497
Programming Projects 498
Chapter 9 Pointers and Dynamic Arrays 507
9.1 POINTERS 508
Pointer Variables 509
Basic Memory Management 516
xxiv contents
Pitfall: Dangling Pointers 517
Static Variables and Automatic Variables 518
Programming Tip: Define Pointer Types 518
9.2 DYNAMIC ARRAYS 521
Array Variables and Pointer Variables 521
Creating and Using Dynamic Arrays 522
Pointer Arithmetic (Optional) 528
Multidimensional Dynamic Arrays (Optional) 530
Chapter Summary 532
Answers to Self-Test Exercises 532
Practice Programs 533
Programming Projects 534
Chapter 10 Defining Classes 541
10.1 STRuCTuRES 542
Structures for Diverse Data 542
Pitfall: Forgetting a Semicolon in a Structure Definition 547
Structures as Function Arguments 548
Programming Tip: Use Hierarchical Structures 549
Initializing Structures 551
10.2 CLASSES 554
Defining Classes and Member Functions 554
Public and Private Members 559
Programming Tip: Make All Member Variables Private 567
Programming Tip: Define Accessor and Mutator Functions 567
Programming Tip: Use the Assignment Operator
with Objects 569
Programming Example: BankAccount Class—Version 1 570
Summary of Some Properties of Classes 574
Constructors for Initialization 576
Programming Tip: Always Include a Default Constructor 584
Pitfall: Constructors with No Arguments 585
Member Initializers and Constructor Delegation in C++11 587
10.3 ABSTRACT DATA TYPES 588
Classes to Produce Abstract Data Types 589
Programming Example: Alternative Implementation of a Class 593
contents xxv
10.4 INTRODuCTION TO INHERITANCE 598
Derived Classes 599
Defining Derived Classes 600
Chapter Summary 604
Answers to Self-Test Exercises 605
Practice Programs 611
Programming Projects 612
Chapter 11 Friends, Overloaded Operators, and Arrays in Classes 619
11.1 FRIEND FuNCTIONS 620
Programming Example: An Equality Function 620
Friend Functions 624
Programming Tip: Define Both Accessor Functions and Friend
Functions 626
Programming Tip: Use Both Member and Nonmember
Functions 628
Programming Example: Money Class (Version 1) 628
Implementation of digit_to_int (Optional) 635
Pitfall: Leading Zeros in Number Constants 636
The const Parameter Modifier 638
Pitfall: Inconsistent Use of const 639
11.2 OVERLOADINg OPERATORS 643
Overloading Operators 644
Constructors for Automatic Type Conversion 647
Overloading Unary Operators 649
Overloading >> and << 650
11.3 ARRAYS AND CLASSES 660
Arrays of Classes 660
Arrays as Class Members 664
Programming Example: A Class for a Partially Filled Array 665
11.4 CLASSES AND DYNAMIC ARRAYS 667
Programming Example: A String Variable Class 668
Destructors 671
Pitfall: Pointers as Call-by-Value Parameters 674
xxvi contents
Copy Constructors 675
Overloading the Assignment Operator 680
Chapter Summary 683
Answers to Self-Test Exercises 683
Practice Programs 693
Programming Projects 694
Chapter 12 Separate Compilation and Namespaces 703
12.1 SEPARATE COMPILATION 704
ADTs Reviewed 705
Case Study: DigitalTime —A Class Compiled Separately 706
Using #ifndef 715
Programming Tip: Defining Other Libraries 718
12.2 NAMESPACES 719
Namespaces and using Directives 719
Creating a Namespace 721
Qualifying Names 724
A Subtle Point About Namespaces (Optional) 725
Unnamed Namespaces 726
Programming Tip: Choosing a Name for a Namespace 731
Pitfall: Confusing the Global Namespace and the Unnamed
Namespace 732
Chapter Summary 733
Answers to Self-Test Exercises 734
Practice Programs 736
Programming Projects 738
Chapter 13 Pointers and Linked Lists 739
13.1 NODES AND LINKED LISTS 740
Nodes 740
nullptr 745
Linked Lists 746
Inserting a Node at the Head of a List 747
Pitfall: Losing Nodes 750
Searching a Linked List 751
contents xxvii
Pointers as Iterators 755
Inserting and Removing Nodes Inside a List 755
Pitfall: Using the Assignment Operator with Dynamic
Data Structures 757
Variations on Linked Lists 760
Linked Lists of Classes 762
13.2 STACKS AND quEuES 765
Stacks 765
Programming Example: A Stack Class 766
Queues 771
Programming Example: A Queue Class 772
Chapter Summary 776
Answers to Self-Test Exercises 776
Practice Programs 779
Programming Projects 780
Chapter 14 Recursion 789
14.1 RECuRSIVE FuNCTIONS FOR TASKS 791
Case Study: Vertical Numbers 791
A Closer Look at Recursion 797
Pitfall: Infinite Recursion 799
Stacks for Recursion 800
Pitfall: Stack Overflow 802
Recursion Versus Iteration 802
14.2 RECuRSIVE FuNCTIONS FOR VALuES 804
General Form for a Recursive Function That Returns a Value 804
Programming Example: Another Powers Function 804
14.3 THINKINg RECuRSIVELY 809
Recursive Design Techniques 809
Case Study: Binary Search—An Example of Recursive Thinking 810
Programming Example: A Recursive Member Function 818
Chapter Summary 822
Answers to Self-Test Exercises 822
Practice Programs 827
Programming Projects 827
xxviii contents
Chapter 15 Inheritance 833
15.1 INHERITANCE BASICS 834
Derived Classes 837
Constructors in Derived Classes 845
Pitfall: Use of Private Member Variables from the Base Class 848
Pitfall: Private Member Functions Are Effectively Not Inherited 850
The protected Qualifier 850
Redefinition of Member Functions 853
Redefining Versus Overloading 856
Access to a Redefined Base Function 858
15.2 INHERITANCE DETAILS 859
Functions That Are Not Inherited 859
Assignment Operators and Copy Constructors in Derived Classes 860
Destructors in Derived Classes 861
15.3 POLYMORPHISM 862
Late Binding 863
Virtual Functions in C++ 864
Virtual Functions and Extended Type Compatibility 869
Pitfall: The Slicing Problem 873
Pitfall: Not Using Virtual Member Functions 874
Pitfall: Attempting to Compile Class Definitions Without
Definitions for Every Virtual Member Function 875
Programming Tip: Make Destructors Virtual 875
Chapter Summary 877
Answers to Self-Test Exercises 877
Practice Programs 881
Programming Projects 884
Chapter 16 Exception Handling 893
16.1 ExCEPTION-HANDLINg BASICS 895
A Toy Example of Exception Handling 895
Defining Your Own Exception Classes 904
Multiple Throws and Catches 904
Pitfall: Catch the More Specific Exception First 908
Programming Tip: Exception Classes Can Be Trivial 909
Throwing an Exception in a Function 909
contents xxix
Exception Specification 911
Pitfall: Exception Specification in Derived Classes 913
16.2 PROgRAMMINg TECHNIquES FOR ExCEPTION HANDLINg 914
When to Throw an Exception 914
Pitfall: Uncaught Exceptions 916
Pitfall: Nested try-catch Blocks 916
Pitfall: Overuse of Exceptions 916
Exception Class Hierarchies 917
Testing for Available Memory 917
Rethrowing an Exception 918
Chapter Summary 918
Answers to Self-Test Exercises 918
Practice Programs 920
Programming Projects 921
Chapter 17 Templates 925
17.1 TEMPLATES FOR ALgORITHM ABSTRACTION 926
Templates for Functions 927
Pitfall: Compiler Complications 931
Programming Example: A Generic Sorting Function 933
Programming Tip: How to Define Templates 937
Pitfall: Using a Template with an Inappropriate Type 938
17.2 TEMPLATES FOR DATA ABSTRACTION 939
Syntax for Class Templates 939
Programming Example: An Array Class 942
Chapter Summary 949
Answers to Self-Test Exercises 949
Practice Programs 953
Programming Projects 953
Chapter 18 Standard Template Library 957
18.1 ITERATORS 959
using Declarations 959
Iterator Basics 960
xxx contents
Programming Tip: Use auto to Simplify Variable Declarations 964
Pitfall: Compiler Problems 964
Kinds of Iterators 966
Constant and Mutable Iterators 970
Reverse Iterators 971
Other Kinds of Iterators 972
18.2 CONTAINERS 973
Sequential Containers 974
Pitfall: Iterators and Removing Elements 978
Programming Tip: Type Definitions in Containers 979
Container Adapters stack and queue 979
Associative Containers set and map 983
Programming Tip: Use Initialization, Ranged For,
and auto with Containers 990
Efficiency 990
18.3 gENERIC ALgORITHMS 991
Running Times and Big-O Notation 992
Container Access Running Times 995
Nonmodifying Sequence Algorithms 997
Container Modifying Algorithms 1001
Set Algorithms 1003
Sorting Algorithms 1004
Chapter Summary 1005
Answers to Self-Test Exercises 1005
Practice Programs 1007
Programming Projects 1008
APPENDICES
1 C++ Keywords 1015
2 Precedence of Operators 1016
3 The ASCII Character Set 1018
4 Some Library Functions 1019
5 Inline Functions 1026
6 Overloading the Array Index Square Brackets 1027
7 The this Pointer 1029
8 Overloading Operators as Member Operators 1032
INDEx 1034
Introduction to Computers and
C++ Programming
1.1 Computer SyStemS 2 Hardware 2 Software 7 High-Level Languages 8 Compilers 9 History Note 12
1.2 proGrAmmING AND proBLem-SoLVING 12
Algorithms 12 Program Design 15 Object-Oriented Programming 16 The Software Life Cycle 17
1.3 INtroDuCtIoN to C++ 18 Origins of the C++ Language 18 A Sample C++ Program 19
Pitfall: Using the Wrong Slash in \n 23 Programming Tip: Input and Output
Syntax 23 Layout of a Simple C++ Program 24 Pitfall: Putting a Space Before the include
File Name 26 Compiling and Running a C++ Program 26 Pitfall: Compiling a C++11 Program 27 Programming Tip: Getting Your Program
to Run 27
1.4 teStING AND DeBuGGING 29 Kinds of Program Errors 30 Pitfall: Assuming Your Program Is Correct 31
1
Chapter Summary 32 Answers to Self-test exercises 33
practice programs 35 programming projects 36
IntroductIon
In this chapter we describe the basic components of a computer, as well as the basic technique for designing and writing a program. We then show you a sample C++ program and describe how it works.
1.1 computer SyStemS A set of instructions for a computer to follow is called a program. The collection of programs used by a computer is referred to as the software for that computer. The actual physical machines that make up a computer installation are referred to as hardware. As we will see, the hardware for a computer is conceptually very simple. However, computers now come with a large array of software to aid in the task of programming. This software includes editors, translators, and managers of various sorts. The resulting environment is a complicated and powerful system. In this book we are concerned almost exclusively with software, but a brief overview of how the hardware is organized will be useful.
Hardware
There are three main classes of computers: PCs, workstations, and mainframes. A PC (personal computer) is a relatively small computer designed to be used by one person at a time. Most home computers are PCs, but PCs are also widely used in business, industry, and science. A workstation is essentially a larger and more powerful PC. You can think of it as an “industrial-strength” PC. A mainframe is an even larger computer that typically requires some support staff and generally is shared by more than one user. The distinctions between PCs, workstations, and mainframes are not precise, but the terms are commonly used and do convey some very general information about a computer.
A network consists of a number of computers connected so that they may share resources such as printers and may share information. A network might contain a number of workstations and one or more mainframes, as well as shared devices such as printers.
For our purposes in learning programming, it will not matter whether you are working on a PC, a mainframe, or a workstation. The basic configuration of the computer, as we will view it, is the same for all three types of computers.
2
The whole of the development and operation of analysis are now capable of being executed by machinery. . . . As soon as an Analytical Engine exists, it will necessarily guide the future course of science.
CHArles BABBAge (1792–1871)
1.1 Computer Systems 3
The hardware for most computer systems is organized as shown in Display 1.1. The computer can be thought of as having five main components: the input device(s), the output device(s), the processor (also called the CPU, for central processing unit), the main memory, and the secondary memory. The processor, main memory, and secondary memory are normally housed in a single cabinet. The processor and main memory form the heart of a computer and can be thought of as an integrated unit. Other components connect to the main memory and operate under the direction of the processor. The arrows in Display 1.1 indicate the direction of information flow.
An input device is any device that allows a person to communicate information to the computer. Your primary input devices are likely to be a keyboard and a mouse.
An output device is anything that allows the computer to communicate information to you. The most common output device is a display screen, referred to as a monitor. Quite often, there is more than one output device. For example, in addition to the monitor, your computer probably is connected to a printer for producing output on paper. The keyboard and monitor are sometimes thought of as a single unit called a terminal.
Display 1.1 Main Components of a Computer
Main memory
Processor (CPU)
Secondary memory
Input device(s)
Output device(s)
4 CHAPTER 1 / Introduction to Computers and C++ Programming
In order to store input and to have the equivalent of scratch paper for performing calculations, computers are provided with memory. The program that the computer executes is also stored in this memory. A computer has two forms of memory, called main memory and secondary memory. The program that is being executed is kept in main memory, and main memory is, as the name implies, the most important memory. Main memory consists of a long list of numbered locations called memory locations; the number of memory locations varies from one computer to another, ranging from a few thousand to many millions, and sometimes even into the billions. each memory location contains a string of 0s and 1s. The contents of these locations can change. Hence, you can think of each memory location as a tiny blackboard on which the computer can write and erase. In most computers, all memory locations contain the same number of zero/one digits. A digit that can assume only the values 0 or 1 is called a binary digit or a bit. The memory locations in most computers contain eight bits (or some multiple of eight bits). An eight- bit portion of memory is called a byte, so we can refer to these numbered memory locations as bytes. To rephrase the situation, you can think of the computer’s main memory as a long list of numbered memory locations called bytes. The number that identifies a byte is called its address. A data item, such as a number or a letter, can be stored in one of these bytes, and the address of the byte is then used to find the data item when it is needed.
If the computer needs to deal with a data item (such as a large number) that is too large to fit in a single byte, it will use several adjacent bytes to hold the data item. In this case, the entire chunk of memory that holds the data item is still called a memory location. The address of the first of the bytes that make up this memory location is used as the address for this larger memory location. Thus, as a practical matter, you can think of the computer’s main memory as a long list of memory locations of varying sizes. The size of each of these locations is expressed in bytes and the address of the first byte is used as the address (name) of that memory location. Display 1.2 shows a picture of a hypothetical computer’s main memory. The sizes of the memory locations are not fixed, but can change when a new program is run on the computer.
Bytes and Addresses
The fact that the information in a computer’s memory is represented as 0s and 1s need not be of great concern to you when programming in C++
Main memory is divided into numbered locations called bytes. The number associated with a byte is called its address. A group of consecutive bytes is used as the location for a data item, such as a number or letter. The address of the first byte in the group is used as the address of this larger memory location.
1.1 Computer Systems 5
(or in most other programming languages). There is, however, one point about this use of 0s and 1s that will concern us as soon as we start to write programs. The computer needs to interpret these strings of 0s and 1s as numbers, letters, instructions, or other types of information. The computer performs these interpretations automatically according to certain coding schemes. A different code is used for each different type of item that is stored in the computer’s memory: one code for letters, another for whole numbers, another for fractions, another for instructions, and so on. For example, in one commonly used set of codes, 01000001 is the code for the letter A and also for the number 65. In order to know what the string 01000001 in a particular location stands for, the computer must keep track of which code is currently being used for that location. Fortunately, the programmer seldom needs to be concerned with such codes and can safely reason as though the locations actually contained letters, numbers, or whatever is desired.
Display 1.2 Memory locations and Bytes
byte 1 byte 2 byte 3 byte 4 byte 5 byte 6 byte 7 byte 8 byte 9
3 byte location with address 1
2 byte location with address 4
1 byte location with address 6
3 byte location with address 7
Why eight?
A byte is a memory location that can hold eight bits. What is so special about eight? Why not ten bits? There are two reasons why eight is special. First, eight is a power of 2. (8 is 23.) Since computers use bits, which have only two possible values, powers of 2 are more convenient than powers of 10. Second, it turns out that eight bits (one byte) are required to code a single character (such as a letter or other keyboard symbol).
6 CHAPTER 1 / Introduction to Computers and C++ Programming
The memory we have been discussing up until now is the main memory. Without its main memory, a computer can do nothing. However, main memory is only used while the computer is actually following the instructions in a program. The computer also has another form of memory called secondary memory or secondary storage. (The words memory and storage are exact synonyms in this context.) Secondary memory is the memory that is used for keeping a permanent record of information after (and before) the computer is used. some alternative terms that are commonly used to refer to secondary memory are auxiliary memory, auxiliary storage, external memory, and external storage.
Information in secondary storage is kept in units called files, which can be as large or as small as you like. A program, for example, is stored in a file in secondary storage and copied into main memory when the program is run. You can store a program, a letter, an inventory list, or any other unit of information in a file.
several different kinds of secondary memory can be attached to a single computer. The most common forms of secondary memory are hard disks, diskettes, CDs, DVDs, and removable flash memory drives. (Diskettes are also sometimes referred to as floppy disks.) CDs (compact discs) used on computers are basically the same as those used to record and play music, while DVDs (digital video discs) are the same as those used to play videos. CDs and DVDs for computers can be read-only so that your computer can read, but cannot change, the data on the disc; CDs and DVDs for computers can also be read/ write, which can have their data changed by the computer. Hard disks are fixed in place and are normally not removed from the disk drive. Diskettes and CDs can be easily removed from the disk drive and carried to another computer. Diskettes and CDs have the advantages of being inexpensive and portable, but hard disks hold more data and operate faster. Flash drives have largely replaced diskettes today and store data using a type of memory called flash memory. Unlike main memory, flash memory does not require power to maintain the information stored on the device. Other forms of secondary memory are also available, but this list covers most forms that you are likely to encounter.
Main memory is often referred to as RAM or random access memory. It is called random access because the computer can immediately access the data in any memory location. secondary memory often requires sequential access, which means that the computer must look through all (or at least very many) memory locations until it finds the item it needs.
The processor (also known as the central processing unit, or CPU) is the “brain” of the computer. When a computer is advertised, the computer company tells you what chip it contains. The chip is the processor. The processor follows the instructions in a program and performs the calculations specified by the program. The processor is, however, a very simple brain. All it can do is follow a set of simple instructions provided by the programmer. Typical processor instructions say things like “Interpret the 0s and 1s as numbers, and then add the number in memory location 37 to the number in memory location 59, and
1.1 Computer Systems 7
put the answer in location 43,” or “read a letter of input, convert it to its code as a string of 0s and 1s, and place it in memory location 1298.” The processor can add, subtract, multiply, and divide and can move things from one memory location to another. It can interpret strings of 0s and 1s as letters and send the letters to an output device. The processor also has some primitive ability to rearrange the order of instructions. Processor instructions vary somewhat from one computer to another. The processor of a modern computer can have as many as several hundred available instructions. However, these instructions are typically all about as simple as those we have just described.
Software
You do not normally talk directly to the computer, but communicate with it through an operating system. The operating system allocates the computer’s resources to the different tasks that the computer must accomplish. The operating system is actually a program, but it is perhaps better to think of it as your chief servant. It is in charge of all your other servant programs, and it delivers your requests to them. If you want to run a program, you tell the operating system the name of the file that contains it, and the operating system runs the program. If you want to edit a file, you tell the operating system the name of the file and it starts up the editor to work on that file. To most users, the operating system is the computer. Most users never see the computer without its operating system. The names of some common operating systems are UNIX, DOS, Linux, Windows, Mac OS, iOS, and Android.
A program is a set of instructions for a computer to follow. As shown in Display 1.3, the input to a computer can be thought of as consisting of two parts, a program and some data. The computer follows the instructions in the program and in that way performs some process. The data is what we conceptualize as the input to the program. For example, if the program adds two numbers, then the two numbers are the data. In other words, the data is the input to the program, and both the program and the data are input to the computer (usually via the operating system). Whenever we give a computer
Display 1.3 simple View of Running a program
Program
Computer
Data
Output
8 CHAPTER 1 / Introduction to Computers and C++ Programming
both a program to follow and some data for the program, we are said to be running the program on the data, and the computer is said to execute the program on the data. The word data also has a much more general meaning than the one we have just given it. In its most general sense, it means any information available to the computer. The word is commonly used in both the narrow sense and the more general sense.
High-Level Languages
There are many languages for writing programs. In this text we will discuss the C++ programming language and use it to write our programs. C++ is a high-level language, as are most of the other programming languages you are likely to have heard of, such as C, C#, Java, Python, PHP, Pascal, Visual Basic, FOrTrAN, COBOl, lisp, scheme, and Ada. High-level languages resemble human languages in many ways. They are designed to be easy for human beings to write programs in and to be easy for human beings to read. A high-level language, such as C++, contains instructions that are much more complicated than the simple instructions a computer’s processor (CPU) is capable of following.
The kind of language a computer can understand is called a low- level language. The exact details of low-level languages differ from one kind of computer to another. A typical low-level instruction might be the following:
ADD X Y Z
This instruction might mean “Add the number in the memory location called X to the number in the memory location called Y, and place the result in the memory location called Z.” The above sample instruction is written in what is called assembly language. Although assembly language is almost the same as the language understood by the computer, it must undergo one simple translation before the computer can understand it. In order to get a computer to follow an assembly language instruction, the words need to be translated into strings of 0s and 1s. For example, the word ADD might translate to 0110, the X might translate to 1001, the Y to 1010, and the Z to 1011. The version of the instruction above that the computer ultimately follows would then be:
0110 1001 1010 1011
Assembly language instructions and their translation into 0s and 1s differ from machine to machine.
Programs written in the form of 0s and 1s are said to be written in machine language, because that is the version of the program that the computer (the machine) actually reads and follows. Assembly language and machine language are almost the same thing, and the distinction between them will not be important to us. The important distinction is that between
1.1 Computer Systems 9
The complete process of translating and running a C++ program is a bit more complicated than what we show in Display 1.4. Any C++ program you write will use some operations (such as input and output routines) that have already been programmed for you. These items that are already programmed for you (like input and output routines) are already compiled and have their object code waiting to be combined with your program’s object code to produce a complete machine-language program that can be run on the computer. Another program, called a linker, combines the object code for these program pieces with the object code that the compiler produced
machine language and high-level languages like C++: Any high-level language program must be translated into machine language before the computer can understand and follow the program.
Compilers
A program that translates a high-level language like C++ to a machine language is called a compiler. A compiler is thus a somewhat peculiar sort of program, in that its input or data is some other program, and its output is yet another program. To avoid confusion, the input program is usually called the source program or source code, and the translated version produced by the compiler is called the object program or object code. The word code is frequently used to mean a program or a part of a program, and this usage is particularly common when referring to object programs. Now, suppose you want to run a C++ program that you have written. In order to get the computer to follow your C++ instructions, proceed as follows. First, run the compiler using your C++ program as data. Notice that in this case, your C++ program is not being treated as a set of instructions. To the compiler, your C++ program is just a long string of characters. The output will be another long string of characters, which is the machine-language equivalent of your C++ program. Next, run this machine-language program on what we normally think of as the data for the C++ program. The output will be what we normally conceptualize as the output of the C++ program. The basic process is easier to visualize if you have two computers available, as diagrammed in Display 1.4. In reality, the entire process is accomplished by using one computer two times.
Compiler
A compiler is a program that translates a high-level language program, such as a C++ program, into a machine-language program that the computer can directly understand and execute.
10 CHAPTER 1 / Introduction to Computers and C++ Programming
from your C++ program. The interaction of the compiler and the linker are diagrammed in Display 1.5. In routine cases, many systems will do this linking for you automatically. Thus, you may not need to worry about linking in many cases.
Linking
Display 1.4 Compiling and Running a C++ program (Basic Outline)
C++ program Data for C++ program
Compiler
Computer
Machine- language
Computer
Output of C++ program
The object code for your C++ program must be combined with the object code for routines (such as input and output routines) that your program uses. This process of combining object code is called linking and is done by a program called a linker. For simple programs, linking may be done for you automatically.
1.1 Computer Systems 11
SeLf-teSt exerCISeS
1. What are the five main components of a computer?
2. What would be the data for a program to add two numbers?
3. What would be the data for a program that assigns letter grades to students in a class?
4. What is the difference between a machine-language program and a high- level language program?
5. What is the role of a compiler?
6. What is a source program? What is an object program?
7. What is an operating system?
8. What purpose does the operating system serve?
Display 1.5 preparing a C++ program for Running
Complete machine- language code ready to run
Object code for C++ program
Object code for other routines
C++ program
Compiler
Linker
12 CHAPTER 1 / Introduction to Computers and C++ Programming
9. Name the operating system that runs on the computer you use to prepare programs for this course.
10. What is linking?
11. Find out whether linking is done automatically by the compiler you use for this course.
1.2 programmIng and problem-SolvIng The Analytical Engine has no pretensions whatever to originate anything. It can do whatever we know how to order it to perform. It can follow analysis; but it has no power of anticipating any analytical relations or truths. Its prov- ince is to assist us in making available what we are already acquainted with.
ADA AUGUSTA, Countess of Lovelace (1815–1852)
In this section we describe some general principles that you can use to design and write programs. These principles are not particular to C++. They apply no matter what programming language you are using.
Algorithms
When learning your first programming language, it is easy to get the impression that the hard part of solving a problem on a computer is translating your ideas into the specific language that will be fed into the computer. This definitely is not the case. The most difficult part of solving a problem on a computer is discovering the method of solution. After you come up with a method of solution, it is routine to translate your method into the required language, be it C++ or some other programming language. It is therefore helpful to temporarily ignore the programming language and to concentrate instead on for- mulating the steps of the solution and writing them down in plain english, as if the instructions were to be given to a human being rather than a computer. A sequence of instructions expressed in this way is frequently referred to as an algorithm.
A sequence of precise instructions which leads to a solution is called an algorithm. some approximately equivalent words are recipe, method,
HIStory Note Charles Babbage, Ada Augusta
The first truly programmable computer was designed by Charles Babbage, an English mathematician and physical scientist. Babbage began the project sometime before 1822 and worked on it for the rest of his life. Although he never completed the construction of his machine, the design was a conceptual milestone in the history of computing. Much of what we know about Charles Babbage and his computer design comes from the writings of his colleague Ada Augusta, the Countess of Lovelace and the daughter of the poet Byron. Ada Augusta is frequently given the title of the first computer programmer. Her comments, quoted in the opening of the this section, still apply to the process of solving problems on a computer. Computers are not magic and do not, at least as yet, have the ability to formulate sophisticated solutions to all the problems we encounter. Computers simply do what the programmer orders them to do. The solutions to problems are carried out by the computer, but the solutions are formulated by the programmer. Our discussion of computer programming begins with a discussion of how a programmer formulates these solutions.
1.2 Programming and Problem-Solving 13
directions, procedure, and routine. The instructions may be expressed in a programming language or a human language. Our algorithms will be expressed in english and in the programming language C++. A computer program is simply an algorithm expressed in a language that a computer can understand. Thus, the term algorithm is more general than the term program. However, when we say that a sequence of instructions is an algorithm, we usually mean that the instructions are expressed in english, since if they were expressed in a programming language we would use the more specific term program. An example may help to clarify the concept.
Display 1.6 contains an algorithm expressed in english. The algorithm determines the number of times a specified name occurs on a list of names. If the list contains the winners of each of last season’s football games and the name is that of your favorite team, then the algorithm determines how many games your team won. The algorithm is short and simple but is otherwise very typical of the algorithms with which we will be dealing.
Ada Augusta, Countess of Lovelace and the first computer programmer
A model of Babbage’s computer
Charles Babbage
14 CHAPTER 1 / Introduction to Computers and C++ Programming
The instructions numbered 1 through 5 in our sample algorithm are meant to be carried out in the order they are listed. Unless otherwise specified, we will always assume that the instructions of an algorithm are carried out in the order in which they are given (written down). Most interesting algorithms do, however, specify some change of order, usually a repeating of some instruction again and again such as in instruction 4 of our sample algorithm.
The word algorithm has a long history. It derives from the name al- Khowarizmi, a ninth-century Persian mathematician and astronomer. He wrote a famous textbook on the manipulation of numbers and equations. The book was entitled Kitab al-jabr w’almuqabala, which can be translated as Rules for Reuniting and Reducing. The similar-sounding word algebra was derived from the Arabic word al-jabr, which appears in the title of the book and which is often translated as reuniting or restoring. The meanings of the words algebra and algorithm used to be much more intimately related than they are today. Indeed, until modern times, the word algorithm usually referred only to algebraic rules for solving numerical equations. Today, the word algorithm can be applied to a wide variety of kinds of instructions for manipulating symbolic as well as numeric data. The properties that qualify a set of instructions as an algorithm now are determined by the nature of the instructions rather than by the things manipulated by the instructions. To qualify as an algorithm, a set of instructions must completely and unambiguously specify the steps to be taken and the order in which they are taken. The person or machine carrying out the algorithm does exactly what the algorithm says, neither more nor less.
Display 1.6 an algorithm
Algorithm that determines how many times a name occurs in a list of names:
1. Get the list of names. 2. Get the name being checked. 3. Set a counter to zero. 4. Do the following for each name on the list: Compare the name on the list to the name being checked, and if the names are the same, then add one to the counter. 5. Announce that the answer is the number indicated by the counter.
Algorithm
An algorithm is a sequence of precise instructions that leads to a solution.
1.2 Programming and Problem-Solving 15
Program Design
Designing a program is often a difficult task. There is no complete set of rules, no algorithm to tell you how to write programs. Program design is a creative process. still, there is the outline of a plan to follow. The outline is given in diagrammatic form in Display 1.7. As indicated there, the entire program design process can be divided into two phases, the problem-solving phase and the implementation phase. The result of the problem-solving phase is an algorithm, expressed in english, for solving the problem. To produce a program in a programming language such as C++, the algorithm is translated into the programming language. Producing the final program from the algorithm is called the implementation phase.
The first step is to be certain that the task—what you want your program to do—is completely and precisely specified. Do not take this step lightly. If you do not know exactly what you want as the output of your program, you may be surprised at what your program produces. Be certain that you know what the input to the program will be and exactly what information is supposed to be in the output, as well as what form that information should be in. For example, if the program is a bank accounting program, you must know not only the interest rate but also whether interest is to be compounded annually, monthly, daily, or whatever. If the program is supposed to write poetry, you need to determine whether the poems can be in free verse or must be in iambic pentameter or some other meter.
Many novice programmers do not understand the need to design an algorithm before writing a program in a programming language, such as C++, and so they try to short-circuit the process by omitting the problem- solving phase entirely, or by reducing it to just the problem-definition part. This seems reasonable. Why not “go for the mark” and save time? The answer is that it does not save time! experience has shown that the two-phase process will produce a correctly working program faster. The two-phase process simplifies the algorithm design phase by isolating it from the detailed rules of a programming language such as C++. The result is that the algorithm design process becomes much less intricate and much less prone to error. For even a modest-size program, it can represent the difference between a half day of careful work and several frustrating days of looking for mistakes in a poorly understood program.
The implementation phase is not a trivial step. There are details to be concerned about, and occasionally some of these details can be subtle, but it is much simpler than you might at first think. Once you become familiar with C++ or any other programming language, the translation of an algorithm from english into the programming language becomes a routine task.
As indicated in Display 1.7, testing takes place in both phases. Before the program is written, the algorithm is tested, and if the algorithm is found to be deficient, then the algorithm is redesigned. That desktop testing is performed by mentally going through the algorithm and executing the steps yourself.
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For large algorithms this will require a pencil and paper. The C++ program is tested by compiling it and running it on some sample input data. The compiler will give error messages for certain kinds of errors. To find other types of errors, you must somehow check to see whether the output is correct.
The process diagrammed in Display 1.7 is an idealized picture of the program design process. It is the basic picture you should have in mind, but reality is sometimes more complicated. In reality, mistakes and deficiencies are discovered at unexpected times, and you may have to back up and redo an earlier step. For example, as shown in Display 1.7, testing the algorithm might reveal that the definition of the problem was incomplete. In such a case you must back up and reformulate the definition. Occasionally, deficiencies in the definition or algorithm may not be observed until a program is tested. In that case you must back up and modify the problem definition or algorithm and all that follows them in the design process.
Object-Oriented Programming
The program design process that we outlined in the previous section represents a program as an algorithm (set of instructions) for manipulating some data. That is a correct view, but not always the most productive view. Modern programs are usually designed using a method known as object- oriented programming, or OOP. In OOP, a program is viewed as a collection
Display 1.7 program Design process
Translating to C++
Testing
Start
Working program
Desktop testing
Algorithm design
Problem definition
Problem-solving phase
Implementation phase
1.2 Programming and Problem-Solving 17
of interacting objects. The methodology is easiest to understand when the program is a simulation program. For example, for a program to simulate a highway interchange, the objects might represent the automobiles and the lanes of the highway. each object has algorithms that describe how it should behave in different situations. Programming in the OOP style consists of designing the objects and the algorithms they use. When programming in the OOP framework, the term Algorithm design in Display 1.7 would be replaced with the phrase Designing the objects and their algorithms.
The main characteristics of OOP are encapsulation, inheritance, and polymorphism. encapsulation is usually described as a form of information hiding or abstraction. That description is correct, but perhaps an easier- to-understand characterization is to say that encapsulation is a form of simplification of the descriptions of objects. Inheritance has to do with writing reusable program code. Polymorphism refers to a way that a single name can have multiple meanings in the context of inheritance. Having made those statements, we must admit that they hold little meaning for readers who have not heard of OOP before. However, we will describe all these terms in detail later in this book. C++ accommodates OOP by providing classes, a kind of data type combining both data and algorithms.
The Software Life Cycle
Designers of large software systems, such as compilers and operating systems, divide the software development process into six phases collectively known as the software life cycle. The six phases of this life cycle are:
1. Analysis and specification of the task (problem definition)
2. Design of the software (object and algorithm design)
3. Implementation (coding)
4. Testing
5. Maintenance and evolution of the system
6. Obsolescence
We did not mention the last two phases in our discussion of program design because they take place after the program is finished and put into service. However, they should always be kept in mind. You will not be able to add improvements or corrections to your program unless you design it to be easy to read and easy to change. Designing programs so that they can be easily modified is an important topic that we will discuss in detail when we have developed a bit more background and a few more programming techniques. The meaning of obsolescence is obvious, but it is not always easy to accept. When a program is not working as it should and cannot be fixed with a reasonable amount of effort, it should be discarded and replaced with a completely new program.
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SeLf-teSt exerCISeS
12. An algorithm is approximately the same thing as a recipe, but some kinds of steps that would be allowed in a recipe are not allowed in an algorithm. Which steps in the following recipe would be allowed in an algorithm?
Place 2 teaspoons of sugar in mixing bowl. Add 1 egg to mixing bowl. Add 1 cup of milk to mixing bowl. Add 1 ounce of rum, if you are not driving. Add vanilla extract to taste. Beat until smooth. Pour into a pretty glass. Sprinkle with nutmeg.
13. What is the first step you should take when creating a program?
14. The program design process can be divided into two main phases. What are they?
15. explain why the problem-solving phase should not be slighted.
1.3 IntroductIon to c++ Language is the only instrument of science . . .
SAMUEL JOHNSON (1709–1784)
In this section we introduce you to the C++ programming language, which is the programming language used in this book.
Origins of the C++ Language
The first thing that people notice about the C++ language is its unusual name. Is there a C programming language, you might ask? Is there a C– or a C– – language? Are there programming languages named A and B? The answer to most of these questions is no. But the general thrust of the questions is on the mark. There is a B programming language; it was not derived from a language called A, but from a language called BCPl. The C language was derived from the B language, and C++ was derived from the C language. Why are there two pluses in the name C++? As you will see in the next chapter, ++ is an operation in the C and C++ languages, so using ++ produces a nice pun. The languages BCPl and B do not concern us. They are earlier versions of the C programming language. We will start our description of the C++ programming language with a description of the C language.
The C programming language was developed by Dennis ritchie of AT&T Bell laboratories in the 1970s. It was first used for writing and maintaining the
1.3 Introduction to C++ 19
UNIX operating system. (Up until that time UNIX systems programs were written either in assembly language or in B, a language developed by Ken Thompson, who is the originator of UNIX.) C is a general-purpose language that can be used for writing any sort of program, but its success and popularity are closely tied to the UNIX operating system. If you wanted to maintain your UNIX system, you needed to use C. C and UNIX fit together so well that soon not just systems programs, but almost all commercial programs that ran under UNIX were written in the C language. C became so popular that versions of the language were written for other popular operating systems; its use is not limited to computers that use UNIX. However, despite its popularity, C is not without its shortcomings.
The C language is peculiar because it is a high-level language with many of the features of a low-level language. C is somewhere in between the two extremes of a very high level language and a low-level language, and therein lies both its strengths and its weaknesses. like (low-level) assembly language, C language programs can directly manipulate the computer’s memory. On the other hand, C has many features of a high-level language, which makes it easier to read and write than assembly language. This makes C an excellent choice for writing systems programs, but for other programs (and in some sense even for systems programs), C is not as easy to understand as other languages; also, it does not have as many automatic checks as some other high-level languages.
To overcome these and other shortcomings of C, Bjarne stroustrup of AT&T Bell laboratories developed C++ in the early 1980s. stroustrup designed C++ to be a better C. Most of C is a subset of C++, and so most C programs are also C++ programs. (The reverse is not true; many C++ programs are definitely not C programs.) Unlike C, C++ has facilities to do object-oriented programming, which is a very powerful programming technique described earlier in this chapter. The C++ language continues to evolve. Major new features were added in 2011. This version is referred to as C++11. Minor features are expected in 2014 and major features again in 2017.
A Sample C++ Program
Display 1.8 contains a simple C++ program and the screen display that might be generated when a user runs and interacts with this program. The person who runs a program is called the user. The output when the program is run is shown in the sample Dialogue. The text typed in by the user is shown in color to distinguish it from the text output by the program. On the actual screen both texts would look alike. The source code for the program is shown in lines 1–22. The line numbers are shown only for reference. You would not type in the line numbers when entering the program. Keywords with a predefined meaning in C++ are shown in color. These keywords are discussed in Chapter 2. The person who writes the program is called the programmer. Do not confuse the roles of the user and the programmer. The user and the programmer might or might not be the same person. For example, if you write and then run a program, you are both the programmer and the user. With professionally produced programs, the programmer (or programmers) and the user are usually different persons.
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Sample Dialogue
Press return after entering a number.
Enter the number of pods:
10
Enter the number of peas in a pod:
9
If you have 10 pea pods
and 9 peas in each pod, then
you have 90 peas in all the pods.
In the next chapter we will explain in detail all the C++ features you need to write programs like the one in Display 1.8, but to give you a feel for how a C++ program works, we will now provide a brief description of how this particular program works. If some of the details are a bit unclear, do not worry. In this section we just want to give you a feel for what a C++ program is.
The beginning and end of our sample program contain some details that need not concern us yet. The program begins with the following lines:
Display 1.8 a sample C++ program
1 #include
3 int main( ) 4 { 5 int number_of_pods, peas_per_pod, total_peas;
6 cout << "Press return after entering a number.\n"; 7 cout << "Enter the number of pods:\n";
8 cin >> number_of_pods;
9 cout << "Enter the number of peas in a pod:\n"; 10 cin >> peas_per_pod; 11 total_peas = number_of_pods * peas_per_pod; 12 cout << "If you have "; 13 cout << number_of_pods; 14 cout << " pea pods\n"; 15 cout << "and "; 16 cout << peas_per_pod; 17 cout << " peas in each pod, then\n"; 18 cout << "you have "; 19 cout << total_peas; 20 cout << " peas in all the pods.\n";
21 return 0;
22 }
1.3 Introduction to C++ 21
#include
For now we will consider these lines to be a rather complicated way of saying “The program starts here.”
The program ends with the following two lines:
return 0; }
For a simple program, these two lines simply mean “The program ends here.” The lines in between these beginning and ending lines are the heart of
the program. We will briefly describe these lines, starting with the following line:
int number_of_pods, peas_per_pod, total_peas;
This line is called a variable declaration. This variable declaration tells the computer that number_of_pods, peas_per_pod, and total_peas will be used as names for three variables. Variables will be explained more precisely in the next chapter, but it is easy to understand how they are used in this program. In this program the variables are used to name numbers. The word that starts this line, int, is an abbreviation for the word integer and it tells the computer that the numbers named by these variables will be integers. An integer is a whole number, like 1, 2, −1, −7, 0, 205, −103, and so forth.
The remaining lines are all instructions that tell the computer to do something. These instructions are called statements or executable statements. In this program each statement fits on exactly one line. That need not be true, but for very simple programs, statements are usually listed one per line.
Most of the statements begin with either the word cin or cout. These statements are input statements and output statements. The word cin, which is pronounced “see-in,” is used for input. The statements that begin with cin tell the computer what to do when information is entered from the keyboard. The word cout, which is pronounced “see-out,” is used for output, that is, for sending information from the program to the terminal screen. The letter c is there because the language is C++. The arrows, written << or >>, tell you the direction that data is moving. The arrows, << and >>, are called ‘insert’ and ‘extract,’ or ‘put to’ and ‘get from,’ respectively. For example, consider the line:
cout << "Press return after entering a number.\n";
This line may be read, ‘put "Press...number.\n" to cout’ or simply ‘output "Press...number.\n"’. If you think of the word cout as a name for the screen (the output device), then the arrows tell the computer to send the string in quotes to the screen. As shown in the sample dialogue, this causes
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the text contained in the quotes to be written to the screen. The \n at the end of the quoted string tells the computer to start a new line after writing out the text. similarly, the next line of the program also begins with cout, and that program line causes the following line of text to be written to the screen:
Enter the number of pods:
The next program line starts with the word cin, so it is an input statement. let’s look at that line:
cin >> number_of_pods;
This line may be read, ‘get number_of_pods from cin’ or simply ‘input number_of_pods’.
If you think of the word cin as standing for the keyboard (the input device), then the arrows say that input should be sent from the keyboard to the variable number_of_pods. look again at the sample dialogue. The next line shown has a 10 written in bold. We use bold to indicate something typed in at the keyboard. If you type in the number 10, then the 10 appears on the screen. If you then press the return key (which is also sometimes called the Enter key), that makes the 10 available to the program. The statement which begins with cin tells the computer to send that input value of 10 to the variable number_of_pods. From that point on, number_of_pods has the value 10; when we see number_of_pods later in the program, we can think of it as standing for the number 10.
Consider the next two program lines:
cout << "Enter the number of peas in a pod:\n"; cin >> peas_per_pod;
These lines are similar to the previous two lines. The first sends a message to the screen asking for a number. When you type in a number at the keyboard and press the return key, that number becomes the value of the variable peas_ per_pod. In the sample dialogue, we assume that you type in the number 9. After you type in 9 and press the return key, the value of the variable peas_ per_pod becomes 9.
The next nonblank program line, shown below, does all the computation that is done in this simple program:
total_peas = number_of_pods * peas_per_pod;
The asterisk symbol, *, is used for multiplication in C++. so this statement says to multiply number_of_pods and peas_per_pod. In this case, 10 is multiplied by 9 to give a result of 90. The equal sign says that the variable total_peas should be made equal to this result of 90. This is a special use of the equal sign; its meaning here is different than in other mathematical contexts. It gives the variable on the left-hand side a (possibly new) value; in this case it makes 90 the value of total_peas.
1.3 Introduction to C++ 23
The rest of the program is basically more of the same sort of output. Consider the next three nonblank lines:
cout << "If you have "; cout << number_of_pods; cout << " pea pods\n";
These are just three more output statements that work basically the same as the previous statements that begin with cout. The only thing that is new is the second of these three statements, which says to output the variable number_of_pods. When a variable is output, it is the value of the variable that is output. so this statement causes a 10 to be output. (remember that in this sample run of the program, the variable number_of_pods was set to 10 by the user who ran the program.) Thus, the output produced by these three lines is:
If you have 10 pea pods
Notice that the output is all on one line. A new line is not begun until the special instruction \n is sent as output.
The rest of the program contains nothing new, and if you understand what we have discussed so far, you should be able to understand the rest of the program.
pItfALL using the Wrong Slash in \n When you use a \n in a cout statement be sure that you use the backslash, which is written \. If you make a mistake and use /n rather than \n, the compiler will not give you an error message. Your program will run, but the output will look peculiar. ■
■ proGrAmmING tIp Input and output Syntax If you think of cin as a name for the keyboard or input device and think of cout as a name for the screen or the output device, then it is easy to remember the direction of the arrows >> and <<. They point in the direction that data moves. For example, consider the statement:
cin >> number_of_pods;
In the above statement, data moves from the keyboard to the variable number_ of_pods, and so the arrow points from cin to the variable.
On the other hand, consider the output statement:
cout << number_of_pods;
In this statement the data moves from the variable number_of_pods to the screen, so the arrow points from the variable number_of_pods to cout. ■
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Layout of a Simple C++ Program
The general form of a simple C++ program is shown in Display 1.9. As far as the compiler is concerned, the line breaks and spacing need not be as shown there and in our examples. The compiler will accept any reasonable pattern of line breaks and indentation. In fact, the compiler will even accept most unreasonable patterns of line breaks and indentation. However, a program should always be laid out so that it is easy to read. Placing the opening brace, {, on a line by itself and also placing the closing brace, }, on a line by itself will make these punctuations easy to find. Indenting each statement and placing each statement on a separate line makes it easy to see what the program instructions are. later on, some of our statements will be too long to fit on one line and then we will use a slight variant of this pattern for indenting and line breaks. You should follow the pattern set by the examples in this book, or follow the pattern specified by your instructor if you are in a class.
In Display 1.8, the variable declarations are on the line that begins with the word int. As we will see in the next chapter, you need not place all your variable declarations at the beginning of your program, but that is a good default location for them. Unless you have a reason to place them somewhere else, place them at the start of your program as shown in Display 1.9 and in the sample program in Display 1.8. The statements are the instructions that are followed by the computer. In Display 1.8, the statements are the lines that begin with cout or cin and the one line that begins with total_peas followed by an equal sign. statements are often called executable statements. We will use the terms statement and executable statement interchangeably. Notice that each of the statements we have seen ends with a semicolon. The semicolon in statements is used in more or less the same way that the period is used in english sentences; it marks the end of a statement.
Display 1.9 layout of a simple C++ program
1 #include
1.3 Introduction to C++ 25
For now you can view the first few lines as a funny way to say “this is the beginning of the program.” But we can explain them in a bit more detail. The first line
#include
is called an include directive. It tells the compiler where to find information about certain items that are used in your program. In this case iostream is the name of a library that contains the definitions of the routines that handle input from the keyboard and output to the screen; iostream is a file that contains some basic information about this library. The linker program that we discussed earlier in this chapter combines the object code for the library iostream and the object code for the program you write. For the library iostream this will probably happen automatically on your system. You will eventually use other libraries as well, and when you use them, they will have to be named in directives at the start of your program. For other libraries, you may need to do more than just place an include directive in your program, but in order to use any library in your program, you will always need to at least place an include directive for that library in your program. Directives always begin with the symbol #. some compilers require that directives have no spaces around the #, so it is always safest to place the # at the very start of the line and not include any space between the # and the word include.
The following line further explains the include directive that we just explained:
using namespace std;
This line says that the names defined in iostream are to be interpreted in the “standard way” (std is an abbreviation of standard). We will have more to say about this line a bit later in this book.
The third and fourth nonblank lines, shown next, simply say that the main part of the program starts here:
int main() {
The correct term is main function, rather than main part, but the reason for that subtlety will not concern us until Chapter 4. The braces { and } mark the beginning and end of the main part of the program. They need not be on a line by themselves, but that is the way to make them easy to find and we will therefore always place each of them on a line by itself.
The next-to-last line
return 0;
says to “end the program when you get to here.” This line need not be the last thing in the program, but in a very simple program it makes no sense to place it anywhere else. some compilers will allow you to omit this line and will figure out that the program ends when there are no more statements to
26 CHAPTER 1 / Introduction to Computers and C++ Programming
execute. However, other compilers will insist that you include this line, so it is best to get in the habit of including it, even if your compiler is happy without it. This line is called a return statement and is considered to be an executable statement because it tells the computer to do something; specifically, it tells the computer to end the program. The number 0 has no intuitive significance to us yet, but must be there; its meaning will become clear as you learn more about C++. Note that even though the return statement says to end the program, you still must add a closing brace, }, at the end of the main part of your program.
pItfALL putting a Space before the include File name Be certain that you do not have any extra space between the < and the iostream file name (Display 1.9) or between the end of the file name and the closing >. The compiler include directive is not very smart: It will search for a file name that starts or ends with a space! The file name will not be found, producing an error that is quite difficult to locate. You should make this error deliberately in a small program, then compile it. save the message that your compiler produces so you know what the error message means the next time you get that error message. ■
Compiling and Running a C++ Program
In the previous section you learned what would happen if you ran the C++ program shown in Display 1.8. But where is that program and how do you make it run?
You write a C++ program using a text editor in the same way that you write any other document—a term paper, a love letter, a shopping list, or whatever. The program is kept in a file just like any other document you prepare using a text editor. There are different text editors, and the details of how to use them will vary from one to another, so we cannot say too much more about your text editor. You should consult the documentation for your editor.
The way that you compile and run a C++ program also depends on the particular system you are using, so we will discuss these points in only a very general way. You need to learn how to give the commands to compile, link, and run a C++ program on your system. These commands can be found in the manuals for your system and by asking people who are already using C++ on your system. When you give the command to compile your program, this will produce a machine-language translation of your C++ program. This translated version is called the object code for your program. The object code must be linked (that is, combined) with the object code for routines (such as input and output routines) that are already written for you. It is likely that this linking will be done automatically, so you do not need to worry about linking. But on some systems, you may be required to make a separate call to the linker. Again, consult your manuals or a local expert. Finally, you give the command to run your program; how you give
compiling and running a c++ program
VideoNote
1.3 Introduction to C++ 27
that command also depends on the system you are using, so check with the manuals or a local expert.
pItfALL compiling a c++11 program C++11 (formerly known as C++0x) is the most recent version of the standard of the C++ programming language. It was approved on August 12, 2011 by the International Organization for standardization. A C++11 compiler is able to compile and run programs written for older versions of C++. However, the C++11 version includes new language features that are not compatible with older C++ compilers. This means that if you have an older C++ compiler then you may not be able to compile and run C++11 programs.
You may also need to specify whether or not to compile against the C++11 standard. For example, g++ 4.7 requires the compiler flag of –std=c++11 to be added to the command line; otherwise the compiler will assume that the C++ program is written to an older standard. The command line to compile a C++11 program named testing.cpp would look like:
g++ testing.cpp -std=c++11
Check the documentation with your compiler to determine if any special steps are needed to compile C++11 programs and to determine what C++11 language features are supported. ■
■ proGrAmmING tIp getting your program to run Different compilers and different environments might require a slight variation in some details of how you set up a file with your C++ program. Obtain a copy of the program in Display 1.10. It is available for downloading over the Internet. (see the Preface for details.) Alternatively, very carefully type in the program yourself. Do not type in the line numbers. Compile the program. If you get an error message, check your typing, fix any typing mistakes, and recompile the file. Once the program compiles with no error messages, try running the program.
If you get the program to compile and run normally, you are all set. You do not need to do anything different from the examples shown in the book. If this program does not compile or does not run normally, then read on. In what follows we offer some hints for dealing with your C++ setup. Once you get this simple program to run normally, you will know what small changes to make to your C++ program files in order to get them to run on your system.
If your program seems to run, but you do not see the output line
Testing 1, 2, 3
then, in all likelihood, the program probably did give that output, but it disappeared before you could see it. Try adding the following to the end of your program, just before the line return 0; these lines should stop your program to allow you to read the output.
28 CHAPTER 1 / Introduction to Computers and C++ Programming
char letter; cout << "Enter a letter to end the program:\n"; cin >> letter;
The part in braces should then read as follows:
cout << "Testing 1, 2, 3\n"; char letter; cout << "Enter a letter to end the program:\n"; cin >> letter; return 0;
For now you need not understand these added lines, but they will be clear to you by the end of Chapter 2.
If the program does not compile or run at all, then try changing
#include
by adding .h to the end of iostream, so it reads as follows:
#include
If your program requires iostream.h instead of iostream, then you have an old C++ compiler and should obtain a more recent compiler.
If your program still does not compile and run normally, try deleting
using namespace std;
If your program still does not compile and run, then check the documentation for your version of C++ to see if any more “directives” are needed for “console” input/output.
Display 1.10 Testing your C++ setup
1 #include
Sample Dialogue
Testing 1, 2, 3
■
If you cannot compile and run this program, then see the programming tip entitled “Getting Your Program to Run.” It suggests some things to do to get your C++ programs to run on your particular computer setup.
1.4 Testing and Debugging 29
If all this fails, consult your instructor if you are in a course. If you are not in a course or you are not using the course computer, check the documentation for your C++ compiler or check with a friend who has a similar computer setup. The necessary change is undoubtedly very small and, once you find out what it is, very easy.
SeLf-teSt exerCISeS
16. If the following statement were used in a C++ program, what would it cause to be written on the screen?
cout << "C++ is easy to understand.";
17. What is the meaning of \n as used in the following statement (which appears in Display 1.8)?
cout << "Enter the number of peas in a pod:\n";
18. What is the meaning of the following statement (which appears in Display 1.8)?
cin >> peas_per_pod;
19. What is the meaning of the following statement (which appears in Display 1.8)?
total_peas = number_of_pods * peas_per_pod;
20. What is the meaning of this directive?
#include
21. What, if anything, is wrong with the following #include directives?
a. #include
1.4 teStIng and debuggIng “And if you take one from three hundred and sixty-five, what remains?”
“Three hundred and sixty-four, of course.”
Humpty Dumpty looked doubtful. “I’d rather see that done on paper,” he said.
LEWIS CARROLL, Through the Looking-Glass
A mistake in a program is usually called a bug, and the process of eliminating bugs is called debugging. There is colorful history of how this term came into use. It occurred in the early days of computers, when computer hardware was
30 CHAPTER 1 / Introduction to Computers and C++ Programming
extremely sensitive and occupied an entire room. rear Admiral grace Murray Hopper (1906–1992) was “the third programmer on the world’s first large- scale digital computer.” (Denise W. gurer, “Pioneering women in computer science” CACM 38(1):45–54, January 1995.) While Hopper was working on the Harvard Mark I computer under the command of Harvard professor Howard H. Aiken, an unfortunate moth caused a relay to fail. Hopper and the other programmers taped the deceased moth in the logbook with the note “First actual case of bug being found.” The logbook is currently on display at the Naval Museum in Dahlgren, Virginia. This was the first documented computer bug. Professor Aiken would come into the facility during a slack time and inquire if any numbers were being computed. The programmers would reply that they were debugging the computer. For more information about Admiral Hopper and other persons in computing, see robert slater, Portraits in Silicon (MIT Press, 1987). Today, a bug is a mistake in a program. In this section we describe the three main kinds of programming mistakes and give some hints on how to correct them.
Kinds of Program Errors
The compiler will catch certain kinds of mistakes and will write out an error message when it finds a mistake. It will detect what are called syntax errors, because they are, by and large, violation of the syntax (that is, the grammar rules) of the programming language, such as omitting a semicolon.
If the compiler discovers that your program contains a syntax error, it will tell you where the error is likely to be and what kind of error it is likely to be. When the compiler says your program contains a syntax error, you can be confident that it does. However, the compiler may be incorrect about either the location or the nature of the error. It does a better job of determining the location of an error, to within a line or two, than it does of determining the source of the error. This is because the compiler is guessing at what you meant to write down and can easily guess wrong. After all, the compiler cannot read your mind. error messages subsequent to the first one have a higher likelihood of being incorrect with respect to either the location or the nature of the error. Again, this is because the compiler must guess your meaning. If the compiler’s first guess was incorrect, this will affect its analysis of future mistakes, since the analysis will be based on a false assumption.
If your program contains something that is a direct violation of the syntax rules for your programming language, the compiler will give you an error message. However, sometimes the compiler will give you only a warning message, which indicates that you have done something that is not, technically speaking, a violation of the programming language syntax rules, but that is unusual enough to indicate a likely mistake. When you get a warning message, the compiler is saying, “Are you sure you mean this?” At this stage of your development, you should treat every warning as if it were an error until your instructor approves ignoring the warning.
1.4 Testing and Debugging 31
There are certain kinds of errors that the computer system can detect only when a program is run. Appropriately enough, these are called run-time errors. Most computer systems will detect certain run-time errors and output an appropriate error message. Many run-time errors have to do with numeric calculations. For example, if the computer attempts to divide a number by zero, that is normally a run-time error.
If the compiler approved of your program and the program ran once with no run-time error messages, this does not guarantee that your program is correct. remember, the compiler will only tell you if you wrote a syntactically (that is, grammatically) correct C++ program. It will not tell you whether the program does what you want it to do. Mistakes in the underlying algorithm or in translating the algorithm into the C++ language are called logic errors. For example, if you were to mistakenly use the addition sign + instead of the multiplication sign * in the program in Display 1.8, that would be a logic error. The program would compile and run normally but would give the wrong answer. If the compiler approves of your program and there are no run- time errors but the program does not perform properly, then undoubtedly your program contains a logic error. logic errors are the hardest kind to diagnose, because the computer gives you no error messages to help find the error. It cannot reasonably be expected to give any error messages. For all the computer knows, you may have meant what you wrote.
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