IT training teach yourself c in 24 hours (2nd ed ) zhang 2000 02 28

pro-You will profit from reading the book when you start to apply C programs to real lems or move on to learn other programming languages, such as Perl, C++, and Java.. Here is a summary

201 West 103rd St., Indianapolis, Indiana, 46290 USA

Sams Teach Yourself C in 24 Hours, Second Edition

Copyright ©2000 by Sams Publishing

All rights reserved No part of this book shall be reproduced, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photo- copying, recording, or otherwise, without written permission from the pub- lisher No patent liability is assumed with respect to the use of the information contained herein Although every precaution has been taken in the preparation

of this book, the publisher and author assume no responsibility for errors or omissions Nor is any liability assumed for damages resulting from the use of the information contained herein.

International Standard Book Number: 0-672-31861-x Library of Congress Catalog Card Number: 99-067311

Printed in the United States of America

First Printing: February, 2000

05 04 03 6 5 4 3

Trademarks

All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized Sams Publishing cannot attest to the accuracy of this information Use of a term in this book should not be regarded

as affecting the validity of any trademark or service mark.

Warning and Disclaimer

Every effort has been made to make this book as complete and as accurate as possible, but no warranty or fitness is implied The information provided is on

an “as is” basis The author and the publisher shall have neither liability nor responsibility to any person or entity with respect to any loss or damages aris- ing from the information contained in this book.

Contents at a Glance

Part II Operators and Control-flow Statements 89

9 Working with Data Modifiers and Math Functions 141

Part III Pointers and Arrays 173

Part IV Functions and Dynamic Memory Allocation 241

Part V Structure, Union, File I/O, and More 311

Table of Contents

Who Should Read This Book? 1

Special Features of This Book 1

Programming Examples 2

Q&A and Workshop 4

Conventions Used in This Book 4

What You’ll Learn in 24 Hours 4

Part I The Basics of C 9 Hour 1 Taking the First Step 11 What Is C? 12

The ANSI C Standard .15

Assumptions About You 16

Setting Up Your System 16

Hardware 16

Software 16

A Sample C Programming Setup 17

Using Microsoft’s Compiler 18

Using Borland’s Compiler 21

Summary 24

Q&A 25

Workshop 25

Quiz 25

Hour 2 Writing Your First C Program 27 A Simple C Program 28

Comments 29

The #include Directive 31

Header Files 32

Angle Brackets ( < > ) and Double Quotes ( “ “ ) 32

The main() Function 33

The Newline Character ( \n ) 33

The return Statement 34

The exit() Function 34

Compiling and Linking 34

What’s Wrong with My Program? 36

Debugging Your Program 37

Summary 37

Q&A 38

Workshop 38

Quiz 38

Exercises 39

Hour 3 Learning the Structure of a C Program 41 The Basics of a C Program 42

Constants and Variables 42

Expressions 42

Statements 45

Statement Blocks 45

Anatomy of a C Function 46

Determining a Function’s Type 46

Giving a Function a Valid Name 47

Passing Arguments to C Functions 47

The Beginning and End of a Function 48

The Function Body 48

Making Function Calls 49

Summary 51

Q&A 52

Workshop 52

Quiz 52

Exercises 53

Hour 4 Understanding Data Types and Keywords 55 C Keywords 56

The char Data Type 57

Character Variables 58

Character Constants 58

The Escape Character (\) 59

Printing Characters 60

The int Data Type 62

Declaring Integer Variables 62

Showing the Numeric Values of Characters 63

The float Data Type 64

Declaring Floating-Point Variables 64

The Floating-Point Format Specifier ( %f ) 65

The double Data Type 67

Using Scientific Notation 67

Naming a Variable 68

Summary 68

Q&A 68

Workshop 69

Quiz 69

Exercises 70

Hour 5 Handling Standard Input and Output 71 Understanding Standard I/O .72

Getting Input from the User 72

Using the getc() Function 72

Using the getchar() Function 74

Printing Output on the Screen 75

Using the putc() Function 75

Another Function for Writing: putchar() 77

Revisiting the printf() Function 78

Converting to Hex Numbers 79

Specifying the Minimum Field Width 81

Aligning Output 83

Using the Precision Specifier 84

Summary 85

Q&A 86

Workshop 86

Quiz 87

Exercises 87

Part II Operators and Control-flow Statements 89 Hour 6 Manipulating Data 91 Arithmetic Assignment Operators 92

The Assignment Operator ( = ) 92

Combining Arithmetic Operators with = 92

Getting Negations of Numeric Values 95

Incrementing or Decrementing by One 96

Greater Than or Less Than? 98

Using the Cast Operator 101

Summary 102

Q&A 102

Workshop 103

Quiz 103

Exercises 103

Hour 7 Working with Loops 105 The while Loop 106

The do-while Loop 107

Looping Under the Statement 109

Contents vii

The Null Statement 112

Using Complex Expressions in a for Statement 113

Using Nested Loops 116

Summary 118

Q&A 118

Workshop 119

Quiz 119

Exercises 120

Hour 8 Using Conditional Operators 121 Measuring Data Sizes 122

Everything Is Logical 124

The Logical AND Operator ( && ) 124

The Logical OR Operator ( || ) 126

The Logical NEGATION Operator ( ! ) 128

Manipulating Bits 129

Converting Decimal to Hex or Binary 129

Using Bitwise Operators 130

Using Shift Operators 133

What Does x?y:z Mean? 135

Summary 137

Q&A 137

Workshop 138

Quiz 138

Exercises 138

Hour 9 Working with Data Modifiers and Math Functions 141 Enabling or Disabling the Sign Bit 142

The signed Modifier 142

The unsigned Modifier 143

Changing Data Sizes 145

The short Modifier 145

The long Modifier 145

Adding h , l , or L to printf and fprintf Format Specifiers 147

Mathematical Functions in C 148

Calling sin() , cos() , and tan() 149

Calling pow() and sqrt() 150

Summary 152

Q&A 153

Workshop 154

Quiz 154

Exercises 154

Hour 10 Controlling Program Flow 155

Always Saying “ if… ” 156

The if-else Statement 158

Nested if Statements 160

The switch Statement 161

The break Statement 164

Breaking an Infinite Loop 166

The continue Statement 167

The goto Statement 168

Summary 170

Q&A 170

Workshop 171

Quiz 171

Exercises 172

Part III Pointers and Arrays 173 Hour 11 Understanding Pointers 175 What Is a Pointer? 176

Address (Left Value) Versus Content (Right Value) 176

The Address-of Operator ( & ) 177

Declaring Pointers 179

The Dereference Operator ( * ) 182

Null Pointers 183

Updating Variables via Pointers 183

Pointing to the Same Memory Location 184

Summary 186

Q&A 187

Workshop 188

Quiz 188

Exercises 188

Hour 12 Understanding Arrays 189 What Is an Array? 190

Declaring Arrays 190

Indexing Arrays 190

Initializing Arrays 191

The Size of an Array 192

Arrays and Pointers 194

Displaying Arrays of Characters 196

The Null Character ( ‘\0’ ) 198

Multidimensional Arrays 199

Unsized Arrays 201

Summary 203

Q&A 203

Workshop 204

Quiz 204

Exercises 205

Hour 13 Manipulating Strings 207 Declaring Strings 208

What Is a String? 208

Initializing Strings 208

String Constants versus Character Constants 209

How Long Is a String? 212

The strlen() Function 212

Copying Strings with strcpy() 213

Reading and Writing Strings 215

The gets() and puts() Functions 215

Using %s with the printf() Function 217

The scanf() Function 217

Summary 219

Q&A 220

Workshop 221

Quiz 221

Exercises 221

Hour 14 Understanding Scope and Storage Classes 223 Hiding Data 224

Block Scope 224

Nested Block Scope 225

Function Scope 226

Program Scope 227

The Storage Class Specifiers 229

The auto Specifier 229

The static Specifier 230

File Scope and the Hierarchy of Scopes 232

The register Specifier 233

The extern Specifier 233

The Storage Class Modifiers 234

The const Modifier 234

The volatile Modifier 235

Summary 236

Q&A 237

Contents xi

Workshop 238

Quiz 238

Exercises 239

Part IV Functions and Dynamic Memory Allocation 241 Hour 15 Working with Functions 243 Declaring Functions 244

Declaration Versus Definition 244

Specifying Return Types 244

Using Prototypes 245

Making Function Calls 245

Prototyping Functions 247

Functions with No Arguments 248

Using time() , localtime() , and asctime() 249

Functions with a Fixed Number of Arguments 251

Prototyping a Variable Number of Arguments 251

Processing Variable Arguments 252

Learning Structured Programming 255

Summary 255

Q&A 256

Workshop 257

Quiz 257

Exercises 257

Hour 16 Applying Pointers 259 Pointer Arithmetic 259

The Scalar Size of Pointers 260

Pointer Subtraction 263

Pointers and Arrays 264

Accessing Arrays via Pointers 264

Pointers and Functions 266

Passing Arrays to Functions 266

Passing Pointers to Functions 268

Passing Multidimensional Arrays as Arguments 270

Arrays of Pointers 272

Pointing to Functions 274

Summary 276

Q&A 276

Workshop 277

Quiz 277

Exercises 278

Hour 17 Allocating Memory 279

Allocating Memory at Runtime 280

The malloc() Function 280

Releasing Allocated Memory with free() 283

The calloc() Function 286

The realloc() Function 288

Summary 291

Q&A 292

Workshop 293

Quiz 293

Exercises 294

Hour 18 Using Special Data Types and Functions 295 The enum Data Type 296

Declaring the enum Data Type 296

Assigning Values to enum Names 296

Making typedef Definitions 300

Why Use typedef ? 300

Recursive Functions 303

Revisiting the main() Function 305

Command-Line Arguments 305

Receiving Command-Line Arguments 306

Summary 308

Q&A 308

Workshop 309

Quiz 309

Exercises 310

Part V Structure, Union, File I/O, and More 311 Hour 19 Understanding Structures 313 What Is a Structure? 314

Declaring Structures 314

Defining Structure Variables 315

Referencing Structure Members with the Dot Operator 315

Initializing Structures 317

Structures and Function Calls 319

Referencing Structures with Pointers 322

Referencing a Structure Member with -> 324

Arrays of Structures 324

Nested Structures 327

Summary 330

Q&A 330

Workshop 331

Quiz 331

Exercises 332

Hour 20 Understanding Unions 333 What Is a Union? 334

Declaring Unions 334

Defining Union Variables 334

Referencing a Union with or -> 335

Unions versus Structures 337

Initializing a Union 337

The Size of a Union 339

Using Unions 341

Referencing the Same Memory Location Differently 341

Making Structures Flexible 343

Defining Bit Fields with struct 347

Summary 350

Q&A 351

Workshop 352

Quiz 352

Exercises 353

Hour 21 Reading and Writing with Files 355 Files Versus Streams 356

What Is a File? 356

What Is a Stream? 356

Buffered I/O 356

The Basics of Disk File I/O 357

Pointers of FILE 357

Opening a File 357

Closing a File 358

Reading and Writing Disk Files 360

One Character at a Time 360

One Line at a Time 363

One Block at a Time 366

Summary 370

Q&A 370

Workshop 371

Quiz 371

Exercises 372

Contents xiii

Hour 22 Using Special File Functions 373

Random Access to Disk Files 374

The fseek() and ftell() Functions 374

The rewind() Function 378

More Examples of Disk File I/O 378

Reading and Writing Binary Data 378

The fscanf() and fprintf() Functions 381

Redirecting the Standard Streams with freopen() 384

Summary 387

Q&A 387

Workshop 388

Quiz 388

Exercises 389

Hour 23 Compiling Programs: The C Preprocessor 391 What Is the C Preprocessor? 392

The C Preprocessor versus the Compiler 392

The #define and #undef Directives 393

Defining Function-Like Macros with #define 394

Nested Macro Definitions 396

Compiling Your Code Under Conditions 397

The #ifdef and #endif Directives 397

The #ifndef Directive 397

The #if , #elif , and #else Directives 399

Nested Conditional Compilation 402

Summary 405

Q&A 405

Workshop 406

Quiz 406

Exercises 407

Hour 24 Where Do You Go from Here? 409 Creating a Linked List 410

Programming Style 418

Modular Programming 419

Debugging 420

What You Have Learned 420

C Keywords 420

Operators 421

Constants 422

Data Types 423

Expressions and Statements 426

Control Flow Statements 426

Pointers 430

Functions 432

Input and Output (I/O) 433

The C Preprocessor 434

The Road Ahead… 434

Summary 435

Part VI Appendixes 437 Appendix A ANSI Standard Header Files 439 Appendix B Answers to Quiz Questions and Exercises 441 Hour 1, “Taking the First Step” 441

Quiz 441

Hour 2, “Writing Your First C Program” 442

Quiz 442

Exercises 442

Hour 3, “Learning the Structure of a C Program” 443

Quiz 443

Exercises 444

Hour 4, “Understanding Data Types and Keywords” 445

Quiz 445

Exercises 445

Hour 5, “Handling Standard Input and Output” 447

Quiz 447

Exercises 447

Hour 6, “Manipulating Data” 449

Quiz 449

Exercises 449

Hour 7, “Working with Loops” 451

Quiz 451

Exercises 451

Hour 8, “Using Conditional Operators” 453

Quiz 453

Exercises 453

Hour 9, “Working with Data Modifiers and Math Functions” 455

Quiz 455

Exercises 456

Hour 10, “Controlling Program Flow” 458

Quiz 458

Exercises 458

Hour 11, “Understanding Pointers” 460

Quiz 460

Exercises 461

Hour 12, “Understanding Arrays” 462

Quiz 462

Exercises 463

Hour 13, “Manipulating Strings” 465

Quiz 465

Exercises 466

Hour 14, “Understanding Scope and Storage Classes” 467

Quiz 467

Exercises 468

Hour 15, “Working with Functions” 470

Quiz 470

Exercises 470

Hour 16, “Applying Pointers” 473

Quiz 473

Exercises 474

Hour 17, “Allocating Memory” 476

Quiz 476

Exercises 476

Hour 18, “Using Special Data Types and Functions” 480

Quiz 480

Exercises 480

Hour 19, “Understanding Structures” 482

Quiz 482

Exercises 482

Hour 20, “Understanding Unions” 486

Quiz 486

Exercises 486

Hour 21, “Reading and Writing with Files” 490

Quiz 490

Exercises 490

Hour 22, “Using Special File Functions” 494

Quiz 494

Exercises 494

Hour 23, “Compiling Programs: The C Preprocessor” 499

Quiz 499

Exercises 500

About the Author

T ONY Z HANGhas more than 15 years experience in computer programming and prise-wide information system design He is currently working for one of the “big 5”consulting firms focusing on e-business related infrastructure design, development, andimplementation

enter-With a Masters degree in Physics, he has published dozens of research papers on lasersand computer programming Among his broad interests are oil painting and photography,the two things that Tony enjoys most

You can reach Tony through Sams Publishing, or by emailing him at

tyc24h@hotmail.com

About the Contributing Author

J OHN S OUTHMAYDis a Software Design Engineer with experience in areas ranging fromsystems-level programming and device drivers to Windows development and Internettechnologies He currently works as a consultant with Excell Data Corporation and liveswith his wife in Kirkland, Washington

It’s my great pleasure to work with editor Sharon Cox for the second time I’d like tothank editors Carol Ackerman and Gus Miklos, and contributing author John Southmaydfor their excellent work that made the second edition of the book more accessible, andlargely, if not completely, error-free Also, I’d like to express my appreciation to the greatwork of the other editing team members Together, they made the second edition possible.

I greatly appreciate the love and support of my wife, Ellen, who inspires me to look atthe technology world from different perspectives It’s always a great joy to discuss issues

on philosophy and literature with her My parents, whom I can never thank enough, gave

me not only love and affection, but also the opportunity of receiving the best education Icould ever have when I was in China

Tell Us What You Think!

As the reader of this book, you are our most important critic and commentator We value

your opinion and want to know what we’re doing right, what we could do better, whatareas you’d like to see us publish in, and any other words of wisdom you’re willing topass our way

As an Associate Publisher for Sams, I welcome your comments You can fax, email, orwrite me directly to let me know what you did or didn’t like about this book—as well aswhat we can do to make our books stronger

Please note that I cannot help you with technical problems related to the topic of this book, and that due to the high volume of mail I receive, I might not be able to reply to every message.

When you write, please be sure to include this book’s title and author as well as yourname and phone or fax number I will carefully review your comments and share themwith the author and editors who worked on the book

Fax: 317-581-4770Email: michael.stephens@macmillanusa.com

Mail: Michael Stephens

Associate PublisherSams Publishing

201 West 103rd StreetIndianapolis, IN 46290 USA

If one learns from others but does not think, one will be bewildered;

If one thinks but does not learn from others, one will be in peril

—Confucius

Welcome to the second edition of Teach Yourself C in 24 Hours!

Based on the success of the first edition of the book and the feedback from the readers,

we have re-written or modified every single chapter of the book to make the second tion more suitable for beginners like you who want to get started with the C program-ming language as quickly as possible

edi-Of course, it’s very normal to spend more than 24 hours to really understand the cepts and programming skills introduced in the book However, the good news is thatthis book offers many sample programs and exercises with clear explanations andanswers, which makes the concepts of the C language easier to understand

con-In fact, Teach Yourself C in 24 Hours provides a good starting point for you in C

pro-gramming It covers important topics in C programming, and lays a solid foundation for

a serious beginner like you After reading this book, you’ll be able to write basic C grams on your own

pro-You will profit from reading the book when you start to apply C programs to real lems or move on to learn other programming languages, such as Perl, C++, and Java

prob-Who Should Read This Book?

If this is your first time learning C, this book is written for you In fact, in writing thisbook I assume that the readers have no previous programming experience Of course, it’salways a big plus if you have some knowledge of computers

Special Features of This Book

This book contains the following special elements that make it simpler and clearer foryou to digest the rudimentary features and concepts of C as they are introduced:

• Syntax boxes

• Notes

• Cautions

• Tips

Syntax boxes explain some of the more complicated features of C, such as control

struc-tures Each syntax box consists of a formal definition of the feature followed by anexplanation Here is an example of a syntax box:

The syntax for the malloc()function is

#include <stdlib.h>

void *malloc(size_t size);

Here,sizespecifies the number of bytes of storage to allocate The header file,

stdlib.h, has to be included before the malloc()function can be called Because the

malloc()function returns a voidpointer, its type is automatically converted to the type

of pointer on the left side of an assignment operator

(You’ll learn more about the malloc()function later in the book.)

Notes are explanations of interesting properties of a particular C program feature Let’s

have a look at the following example of a note:

at the right end of the value field.

Warnings warn you of programming pitfalls you should avoid Here is a typical warning:

Never use the reserved keywords in C, nor names of the C library functions

as variable names in your program.

Tips are hints on how to write your C programs better The following is an example of

expla-Each example has a listing of the C program; the output generated from that listing willfollow The example also offers an analysis of how the program works Special icons areused to point out each part of the example: Type, Input/Output, and Analysis.

In the example shown in Listing IN.1, there are some special typographic conventions

The input you enter is shown in bold monospace type, and the output generated by theexecutable program of Listing IN.1 is shown in plain monospace type

L ISTING IN.1 Read in a Character Entered by the User

1: /* INL01.c: Read input by calling getc() */

2: #include <stdio.h>

3:

4: main() 5: { 6: int ch;

Please type in one character:

H The character you just entered is: H

In line 2 of Listing IN.1, the header file stdio.his included for both the getc()

and printf()functions used in the program Lines 4–12 give the name and body

of the main()function

In line 6, an integer variable chis declared, which is assigned to the return value fromthe getc()function later in line 9 Line 8 prints out a piece of message that asks the user

to enter one character from the keyboard The printf()function in line 8 uses thedefault standard output stdoutto display messages on the screen

In line 9, the standard input stdinis passed to the getc()function, which indicates thatthe file stream is from the keyboard After the user types in a character, the getc()func-tion returns the numeric value (that is, an integer) of the character Note that in line 9 thenumeric value is assigned to the integer variable ch

Introduction 3

TYPE

In line 10, the character entered is displayed on the screen with the help of printf().Note that the character format specifier %cis used within the printf()function in line 10.

Q&A and Workshop

Each hour (that is, each chapter) ends with a Q&A section that contains answers to mon questions relating to the lesson of the chapter Following the Q&A section there is aWorkshop that consists of quiz questions and programming exercises The answers tothese quiz questions and sample solutions for the exercises are presented in Appendix D,

com-“Answers to Quiz and Exercises.”

To help you solidify your understanding of each lesson, you are encouraged to try toanswer the quiz questions and finish the exercises provided in the workshop

Conventions Used in This Book

This book uses special typefaces to help you differentiate between C code and regularEnglish, and to identify important concepts

• Actual C code is typeset in a special monospacefont You’ll see this font used inlistings, Input/Ouput examples, and code snippets In the explanation of C features,commands, filenames, statements, variables, and any text you see on the screen arealso typeset in this font

• Command input and anything that you are supposed to enter appears in a bold monospacefont You’ll see this mainly in the Input/Output sections of examples

• Placeholders in syntax descriptions appear in an italic monospacefont Replacethe placeholder with the actual filename, parameter, or whatever element it repre-sents

• Italics highlight technical terms when they appear for the first time in the text and

are sometimes used to emphasize important points

What You’ll Learn in 24 Hours

Teach Yourself C in 24 Hours consists of five parts In Part I, “The Basics of C,” you’ll

learn the basics of the C language Here is a summary of what you’re going to learn:

Hour 1, “Taking the First Step,” introduces you to the C language, the ANSI

stan-dard, and the basic software and hardware requirements for C programming

Hour 2, “Your First C Program,” demonstrates the entire procedure of writing,

compiling, linking, and running a C program

Hour 3, “Learning the Structure of a C Program,” teaches you several important

concepts, such as constants, variables, expressions, and statements The anatomy of afunction is introduced in this hour as well

Hour 4, “Understanding Data Types and Keywords,” lists all reserved C keywords.

Four data types,char,int,float, and double, are introduced in detail Also, the rulesfor naming a variable are explained

Hour 5, “Handling Standard Input and Output,” teaches you to receive input from

the keyboard, and print output on the screen with the help of a set of C functions,such as getc(),getchar(),putc(),putchar(), and printf()

Part II, “Operators and Control-flow Statements,” emphasizes operators and control-flowstatements in C The following is a summary of what you’ll learn:

Hour 6, “Manipulating Data,” teaches you how to use arithmetic assignment

opera-tors, the unary minus operator, increment/decrement operaopera-tors, relational operaopera-tors,and the cast operator

Hour 7, “Working with Loops,” introduces looping (that is, iteration) with the for,

while, or do-whilestatements

Hour 8, “Using Conditional Operators,” tells you about more operators, such as

logical operators, bitwise operators, the sizeofoperator, and ?:operator, which arefrequently used in C

Hour 9, “Working with Data Modifiers and Math Functions,” describes how to

use data modifiers to enable or disable the sign bit, or change the size of a data type

Also, several mathematical functions provided by C are introduced

Hour 10, “Controlling Program Flow,” introduces all the control-flow statements

used in C They are the if,if-else,switch,break,continue, and gotostatements

Pointers and arrays are discussed in Part III, “Pointers and Arrays.” The following is asummary of what you’ll learn:

Hour 11, “Understanding Pointers,” teaches you how to reference variables with

pointers Concepts such as left value and right value are also introduced

Hour 12, “Understanding Arrays,” explains how to declare and initialize arrays.

The relationship between the array and the pointer in C is discussed too

Hour 13, “Manipulating Strings” focuses on reading and writing strings Several C

library functions, such as strlen(),strcpy(),gets(),puts(), and scanf(), areintroduced to manipulate strings

Hour 14, “Understanding Scope and Storage Classes,” introduces block scope,

func-tion scope, program scope, and file scope In addifunc-tion, storage class specifiers or fiers, such as auto,static,register,extern,const, and volatileare explained

modi-Introduction 5

Part IV, “Functions and Dynamic Memory Allocation,” focuses on functions anddynamic memory allocations in C The following is a summary of what you’ll learn:

Hour 15, “Working with Functions,” describes the function declaration and

defini-tion in C The funcdefini-tion prototyping is explained, along with the funcdefini-tion return typespecification

Hour 16, “Applying Pointers” teaches you how to perform pointer arithmetic

opera-tions, access elements in arrays with pointers, and how to pass pointers to functions

Hour 17, “Allocating Memory” explains the concept of allocating memory

dynami-cally C functions, such as malloc(),calloc(),realloc(), and free(), are duced with regard to the dynamic memory allocation

intro-Hour 18, “Using Special Data Types and Functions,” introduces the enumdata typeand the use of typedef Function recursion and command-line arguments to the

main()function are also taught in Hour 18

Part V, “Structure, Union, File I/O, and More,” discusses structures, unions, and disk fileI/O in C The following is a summary of what you’ll learn:

Hour 19, “Understanding Structures,” introduces the structuredata type Youlearn to access structure members, and pass structures to functions with the help ofpointers Nested and forward-referencing structures are also discussed in this hour

Hour 20, “Understanding Unions,” describes the uniondata type, and the differencebetween unionand structure The applications of unions are demonstrated in severalexamples

Hour 21, “Reading and Writing with Files,” explains the concepts of the file and

the stream in C The basics of disk file input and output are introduced in this firstpart The following C functions, along with several examples are, introduced in thishour:fopen(),fclose(),fgetc(),fputc(),fgets(),fputs(),fread(),fwrite(),and feof()

Hour 22, “Using Special File Functions,” is the second part of disk file I/O, in

which fseek(),ftell(), and rewind()are introduced to show how they can helpyou to get random access to disk files In addition, the fscanf(),fprintf(), and

freopen()functions are taught and invoked in sample programs

Hour 23, “Compiling Programs: The C Preprocessor,” describes the role played by

the C preprocessor You can learn the preprocessor directives, such as #define,

#undef,#ifdef,#endif,#ifndef,#if,#elis, and #elsethrough the examples given

in this hour

Hour 24, “Where Do You Go from Here?,” summarizes the important concepts and

features introduced in this book In addition, programming style, modular ming, and debugging are explained briefly A list of recommended C books is pro-vided for your further reading

program-Now, you’re ready to start the journey of learning the C language, as the world has movedinto a new millennium Have a fun in reading this book, and enjoy programming in C!

Tony ZhangDowningtown, PennsylvaniaJanuary, 2000

Introduction 7

1 Taking the First Step

2 Your First C Program

3 Learning the Structure of a C program

4 Understanding Data Types and Keywords

5 Handling Standard Input and Output

The Basics of C

H OUR 1

Taking the First Step

A journey of a thousand miles is started by taking the first step.

• Why you need to learn C

• The ANSI standard

• Hardware and software required to write and run C programs

What Is C?

C is a programming language The C language was first developed in 1972 by Dennis

Ritchie at AT&T Bell Labs Ritchie called his newly developed language C simply because there was a B programming language already (As a matter of fact, the B lan-

guage led to the development of C.)

C is a high-level programming language In fact, C is one of the most popular purpose programming languages

general-In the computer world, the further a programming language is from the computer tecture, the higher the language’s level You can imagine that the lowest-level languagesare machine languages that computers understand and execute directly The high-levelprogramming languages, on the other hand, are closer to our human languages (seeFigure 1.1)

archi-F IGURE 1.1

The language

to the Internet;

else, wait

If (line ! = busy) connect (Internet);

else wait (5)

10001111101100 01100111011000 Low

High

High-level programming languages, including C, have the following advantages:

• Readability: Programs are easy to read.

• Maintainability: Programs are easy to maintain.

• Portability: Programs are easy to port across different computer platforms.

The C language’s readability and maintainability benefit directly from its relative ness to human languages, especially English.

close-Each high-level language needs a compiler or an interpreter to translate instructions

written in the high-level programming language into a machine language that a puter can understand and execute Different machines may need different compilers orinterpreters for the same programming language For instance, I use Microsoft’s C com-piler to compile the C programs in this book for my personal computer (PC) If I need torun the C programs on a UNIX-based workstation, I have to use another type of C com-piler to compile these programs Therefore, the portability of programs written in C isrealized by re-compiling the programs with different compilers for different machines(see Figure 1.2)

com-Taking the First Step 13

1

F IGURE 1.2

Porting programs

writ-ten in C into different

types of computers.

The C Program

Compiler A

Compiler B

Compiler C

The Computer’s Brain

You may know that the brain of a computer is the central processing unit (CPU) Some computers may have more than one CPU inside A CPU has millions of transistors that make use of electronic switches The electronic switches have only two states: off and on.

(Symbolically, 0 and 1 are used to represent the two states.) Therefore, a computer can only understand instructions consisting of series of 0 s and 1 s In other words, machine- readable instructions have to be in binary format.

In addition, the C language has other advantages Programs written in C can be reused.You can save parts of your C programs into a library file and invoke them in your nextprogramming project simply by including the library file Many common and useful pro-gramming tasks are already implemented in libraries that come included with compilers.

In addition, libraries allow you to easily unleash the power and functionality of the ating system you are using More details on using C library functions are covered in therest of this book

oper-C is a relatively small programming language, which makes life easier for you You don’thave to remember many C keywords or commands before you start to write programs in

C to solve problems in the real world

For those who seek speed while still keeping the convenience and elegance of a level language, the C language is probably the best choice In fact, C allows you to getcontrol of computer hardware and peripherals That’s why the C language is sometimescalled the lowest high-level programming language

high-Many other high-level languages have been developed based on C For instance, Perl is apopular programming language in World Wide Web (WWW) design across the Internet.Perl actually borrows a lot of features from C If you understand C, learning Perl is asnap Another example is the C++ language, which is simply an expanded version of C,although C++ makes object-oriented programming easier Also, learning Java becomesmuch easier if you already know C

However, a computer program written in a high-level language, such as C, Java, or Perl, is just a text file, consisting of English-like characters and words You have to use special programs, called compilers or interpreters, to translate such a program into a machine- readable code That is, the text format of all instructions written in a high-level language has to be converted into binary format The code obtained after the translation is called

binary code Prior to the translation, a program in text format is called source code The smallest unit of binary code is called a bit (from binary digit), which can have a value

of 0 or 1 Generally, eight bits make up one byte, and half a byte (four bits) is one nibble.

There are generally two types of programming languages: compiled guages and interpreted languages.

lan-A compiler is needed to translate a program written in a compiled language into machine-understandable code (that is, binary code) before you can run the program on your machine When the translation is done, the binary

The ANSI C Standard

For many years, the de facto standard for the C programming language was the book The

C Programming Language, written by Brian Kernighan and Dennis Ritchie in 1978 This

book is commonly known in the programming community as simply K&R (referring tothe initials of the authors) and finds a place on many programmers’ bookshelves to thisday However, the book was written as a tutorial introduction to C, not as a comprehen-sive or official standard for the language As different vendors offered varying implemen-tations of the C language, differences between those implementations began to appear

Fearing that C might lose its portability, a group of compiler vendors and software opers petitioned the American National Standards Institute (ANSI) to build a standard forthe C language in 1983 ANSI approved the application and formed the X3J11 TechnicalCommittee to work on the C standard By the end of 1989, the committee approved theANSI standard for the C programming language

devel-The ANSI standard for C enhances the original K&R standard and defines a group ofcommonly used C functions that known as the ANSI C standard library In most cases, Ccompilers include the standard library, along with other libraries to provide some othercompiler-specific functions

Taking the First Step 15

1

code can be saved into an application file You can keep running the cation file without the compiler unless the program (source code) is updated and you have to recompile it The binary code or application file is also called executable code (or an executable file).

appli-On the other hand, a program written in an interpreted language can be run immediately after you finish writing it — or for that matter, while you are writing it! But such a program always needs an interpreter to translate the high-level instructions into machine-understandable instructions (binary code) at runtime You cannot run the program on a machine unless the right interpreter is available.

You can think of the C language as a compiled language because most C language vendors make only C compilers, as opposed to interpreters, to sup- port programs written in C.

However, there is nothing inherent to a compiled language to prevent someone from providing an interpreter for the language; likewise, people can and often do write compilers for interpreted languages In fact, it is not uncommon to mix the two flavors of languages, where a programmer com- piles source code into a small binary file which is then executed by a runtime interpreter.

This book focuses on the C functions defined in the ANSI standard, which is supported

by all compiler vendors All programs in this book can be compiled by any compilersthat comply with the ANSI standard If you’re interested in a specific compiler, you canlearn the compiler-specific functions from the compiler’s reference manual

Assumptions About You

No previous programming experience is required for you to learn the C language from thisbook, although some knowledge of computers helps Also, it’s up to you to determine howquickly to go through the 24 hours of this book: You could sit up with a big pot of coffeeand power through the book in a sitting or you could take an hour a day for 24 days.After you complete this book, having done all of the exercises along the way, you should

be proficient and comfortable with the syntax and features of the C language In addition,you’ll already have some experience with many of the tasks that are encountered in Cprogramming When you’re ready to undertake your own programming projects, you’ll

be able to use C as a tool in writing the powerful and useful programs you want to ate As you progress, you’ll find that there is always more to learn—not only about Cand how to leverage its power, but also about new technologies and programming ideas

cre-in general With hard work and lots of practice, you can quickly build on the skills andtechnologies that you learn

Setting Up Your System

Basically, all you need is a computer and a C compiler in order to compile and run yourown C programs or the C programs from this book The recommended hardware andsoftware are listed in the following sections

Hardware

Any type of computer that has or can access a C compiler is fine The C compiler should

be ANSI C compliant Most likely, you have a PC on your desktop A 286 PC with a50MB hard drive and 1MB memory (RAM) is probably the minimum requirement to run

a DOS-based C compiler For a Windows-based C compiler, your computer must have abigger hard drive and more memory Check your compiler vendor for more details onhardware requirements

Software

If you’re using a UNIX-based workstation, you might already have a C compiler loaded

on your machine, or at least you might be able to access a C compiler on a servermachine Check with your system administrator to find out how to access an ANSI C

compliant compiler On a UNIX-based machine, you should know how to use a text tor such as vior emacsto write C programs.

edi-If you have a PC running a Microsoft Windows operating system (such as Windows 95),you need to install a C compiler and a text editor on your PC However, most C compil-ers come with a built-in editor You can also use any text editor that may already beinstalled on your machine

Borland International’s Turbo C and Microsoft’s Quick C used to be very popular in the

C compiler market These days, an ANSI-compliant C compiler is usually part of anycommercially available C++ development package, such as Microsoft Visual C++ Inaddition, development packages come with an integrated development environment(IDE), which you can use to edit, compile, run, and debug your C programs all from thesame window

You can pick up any C compiler you like to compile the sample code given in the book,

as long as the compiler is ANSI C compliant You shouldn’t have problems installing a Ccompiler on your computer if you read the manuals that come with the compiler and fol-low the installation instructions correctly Most C and/or C++ compilers provide a quicktutorial that shows you how to install the compiler and set up a working developmentenvironment on your computer

These days, the Linux operating system is becoming more and more popular among PCusers In most cases, the Linux package you get contains a C compiler The C compilercan be installed on your PC when you’re installing the Linux operating system, or can beadded later after you finish the installation of Linux

A Sample C Programming Setup

I have a Pentium 100MHz PC with 32MB memory and with a 2.5GB hard drive (Thehard drive had about 1.5GB free space before I installed a copy of Microsoft Visual C++

5.0.) Also, I have Windows 95 as the operating system on the machine

In this book, all C programs are developed with Microsoft Visual C++ version 5.0 Thereasons I chose Visual C++ are simple: All C programs in this book are written in ANSI

C and can be compiled into console-mode applications (that is, text-based programs ning in a DOS window); the Visual C++ 5.0 package includes a good C compiler that isANSI C compliant

run-I set up my development environment in such a way that all C programs in this book can

be compiled and made into console applications Also, I test and run the applicationsmade from the C programs at a DOS prompt provided by Windows 95

In the following two sections, I’ll briefly show you how to use Microsoft’s and Boralnd’s

C compilers

Taking the First Step 17

1

Using Microsoft’s Compiler

I’m going to show you how to use the C compiler that is bundled with the Microsoft’sVisual C++ package in this section If you need to learn more details on how to installVisual C++, please follow the instructions that come with the compiler

Now I assume you’ve installed a copy of Visual C++ 5.0 on your computer To start thecompiler, you can click the Start button from your Windows 95 (or 98 or NT), andchoose: Programs, Microsoft Visual C++ 5.0, Microsoft Visual C++ 5.0 Or, you cansimply run the application file MSDEV.EXEdirectly from the directory (folder) where youinstalled the Visual C++ package Figure 1.3 shows an example of the integrated devel-opment environment (IDE) from Visual C++ 5.0

F IGURE 1.3

An example of the IDE from Visual C++ ver- sion 5.0.

Then, you can open a new file within the IDE by clicking the New File button on the farleft side of the toolbar, and type the following text in the space of the new file:

#include <stdio.h>

main() { printf (“Howdy, neighbor! This is my first C program.\n”);

return 0;

}

Figure 1.4 shows the IDE with the text you just typed in Don’t worry about the meaning

of the text In the next chapter, “Your First C Program,” will explain it to you

Taking the First Step 19

As dialog box, click the New Folder button and type in a name for your programmingfolder Then double-click that folder to open it, type MyFirstProgram.c in the File Namebox, and click Save Note that the extension .cis used to indicate that the file you justsaved is a C program file

Now, you need to click the Build menu and choose the Compile MyFirstProgram.coption By doing so, you ask the compiler to compile the text you just typed in and saved(see Figure 1.5) At this point, Visual C++ may prompt you to create a new workspace;

just click Yes and this will be done automatically There should be no errors or warnings

in the output window after the compiler is run

Then, click the Build menu again, and this time, choose the Build MyFirstProgram.exeoption which will eventually produce an executable file called MyFirstProgram.exe.Figure 1.6 shows that there are no errors or warnings after MyFirstProgram.exeis built