c语言的艺术.doc

C语言的科学与艺术
　　 Welcome! By picking up this book, you have taken a step into the world of computer science--a field of study that has grown from almost nothing half a century ago to become one of the most vibrant and active disciplines of our time.
　　 Over that time, the computer has opened up extraordinary possibilities in almost every area of human endeavor. Business leaders today are able to manage global enterprises on an unprecedented scale because computers enable them to transfer information anywhere in a fraction of a second. Scientists can now solve problems that were beyond their reach until the computer made the necessary cal-culations possible. Filmmakers use computers to generate dramatic visual effects that are impossible to achieve without them. Doctors can determine much more accurately what is going on inside a patient because computers have enabled a massive transformation in the practice of medicine.
　　 Computers are a profoundly empowering technology. The advances we have seen up to now are small compared to what we will see in the next century. Computers will play a major role in shaping that century, just as they have the last 50 years.
　　Those of you who are students today will soon inherit the responsibility of guiding that progress. As you do so, knowing how to use computers can only help.
　　 Like most skills that are worth knowing, learning how computers work and how to control their enormous power takes time. You will not understand it all at once.But you must start somewhere. Twenty-five centuries ago, the Chinese philosopher Lao-tzu observed that the longest journey begins with a single step. This book can be your beginning.
　　 For many of you, however, the first step can be the hardest to take. Many students find computers overwhelming and imagine that computer science is beyond their reach. Learning the basics of programming, however, does not require advanced mathematics or a detailed understanding of electronics. What matters in programming is whether you can progress from the statement of a problem to its solution. To do so, you must be able to think logically. You must have the neces-
　　sary discipline to express your logic in a form that the computer can understand.Perhaps most importantly, you must be able to see the task through to its completion without getting discouraged by difficulties and setbacks. If you stick with the process, you will discover that reaching the solution is so exhilarating that it more than makes up for any frustrations you encounter along the way.
　　 This book is designed to teach you the fundamentals of programming and the basics of C, which is the dominant programming language in the computing industry today. It treats the whys of programming as well as the hows, to give you a feel for the programming process as a whole. It also includes several features that will help you focus on the essential points and avoid errors that slow you down. The next few pages summarize these features and explain how to use this book effectively as you begin your journey into the exciting world of computer science.

C语言教程前言
A Book on C conveys an appreciation for both the elegant simplicity and the power of this general-purpose programming language. By presenting interactive running programs from many application areas, this book describes the ANSI version of the C language. The complete language is presented in a step-by-step manner, along with many complete working programs.
　　 Where appropriate, we discuss the differences between traditional C and ANSI C.(Traditional C still remains in wide use.) Dozens of example programs are available to illustrate each important language feature, and many tables summarize key information and provide easy access for later reference. Each chapter ends with a summary and exercises. The summary reviews key elements presented in the chapter, and the exercises augment and extend the text.
　　 This book assumes a general-purpose knowledge of the C language. It is intended for use in either a first or second programming course. However, it can be readily used in conjunction with courses on topics such as comparative programming languages, computational linguistics, data structures, database systems, fractal geometry, graphics,numerical analysis, operating systems, programming methodology, and scientific applications. C is suitable for applications from each of these domains, and all features of Cneeded to code such applications are explained. This book is appropriate for a data structures course because advanced data structuring features such as enumeration types, unions, self-referential structures, and ragged arrays are discussed. For operatlng systems courses concerned with UNIX or Windows 95/NT, the book explores the file
　　structure and systems routines that enable the C programmer to add to existing systerns libraries and understand the C code underlying the operating system. For applications programming and soentific programming, there is discussion of how to write sample function libraries. Statistics, root finding, sorting, text manipulation, file handling, and game playing are all represented with working code.
　　 New Java Section. In Chapter 14, "Moving from C to Java," we discuss how the C programmer can very naturally and easily begin programming in Java, a language of interest for work on the Internet. The Java programming language borrows ideas from both C and C++ and is designed to run in a machine-and system-independent manner. This makes it suitable for Internet work, such as writing applets for Web pages that get used by browsers. Because Java is an extension of C and C++, it is readily learned by the C programmer.
　　Complete ANSI C Language. Computer professionals will have access to a complete treatment of the language, including enumeration types, list processing, and the operating system interface. Chapter 1, "An Overview of C," presents an overview of the language. After reading this chapter, the professional will already be able to write C code.
　　Since the chapters are self-contained, the knowledgeable reader can skip to particular sections as needed. Chapter 11, "Input/Output and the Operating System," gives a thorough introduction to the connections to the operating system. This information will benefit the professional systems programmer needing to use C to work within an MSDOS or UNIX environment.
　　Interactive Environment. This book is written entirely with the modern interactive environment in mind. Experimentation is encouraged throughout. Keyboard and screen input/output is taken as the norm, and its attendant concerns are explained. Thus, the book is appropriate for users of small home and business computers as well as to users of large interactive systems. We assume that the reader will have access to an interac tive ANSI C system. During the writing of this book, we used a number of different C systems: various Borland and Microsoft compilers running on IBM-compatible Pentium machines, the GNU gcc compiler and native compilers running on various workstations from DEC, SGI, and Sun, and the C compiler that runs on the Cray supercomputer in San Diego.
　　Working Code. Our approach to describing the language 'is to use examples, explanation, and syntax. Working code is employed throughout. Small but useful examples are provided to describe important technical points. Small because small is comprehensible. Useful because programming is based on a hierarchy of building blocks and ultimately is pragmatic. The programs and functions described in the book can be used in actual systems. The authors' philosophy is that one should experiment and enjoy.
　　Dissections. We use highlighted "dissections" on many programs and functions throughout the book. Dissection is a unique pedagogical tool first developed by the authors in 1984 to illuminate key features of working code. A dissection is similar to a structured walk-through of the code. Its intention is to explain to the reader newly encountered programming elements and idioms found in working code.
　　Flexible Organization. This book is constructed to be very flexible in its use. Chapter 1,
　　"An Overview of C," is in two parts. The first part explains the crucial programming techniques needed for interactive input/output, material that must be understood by all. The second part of Chapter 1 goes on to survey the entire language and will be comprehensible to experienced programmers familiar with comparable features from other languages. This second part can be postponed in a first programming course. Caution:Beginning programmers should postpone the second part of Chapter 1.
　　 Chapter 2, "Lexical Elements, Operators, and the C System," describes the lexical level
　　of the language and syntactic rules, which are selectively employed to illustrate C language constructs. The instructor may decide to teach Backus-Naur-Form (BNF) notation as described in Chapter 2 or may omit it without any loss of continuity. The book uses BNF-style syntactic descriptions so that the student can learn this standard form of programming language description. In addition, language components are thoroughly described by example and ordinary explanation.
　　 Reference Work. This book is designed to be a valuable reference to the C language.Throughout the book, many tables concisely illustrate key areas of the language. The complete ANSI C standard library, along with its associated header files, is described in the Appendix A, "The Standard Library." Sections in the appendix are devoted to explaining each of the standard header files such as ctype, h, stdio, h, and string, h. Where appropriate, example code is given to illustrate the use of a particular construct or function.
　　 In Appendix B, "Language Syntax," we provide the complete syntax of the C language.In Appendix C, "ANSI C Compared to Traditional C," we list the major differences between ANSI C and traditional C. Finally, special care has been taken to make the index easy to use and suitable for a reference work.
　　The Complete ANSI C Language. Chapters 3 through 10 cover the C language feature by feature. Many advanced topics are discussed that may be omitted on first reading without loss of comprehension, if so desired. For example, enumeration types are relatively new to the language, and their use can be omitted in a first course. Machine dependent features such as word size considerations and floating-point representation are emphasized, but many of the details need not concern the beginner.
　　The Preprocessor. Chapter 8, "The Preprocessor," is devoted entirely to the preproeessor, which is used to extend the power and notation of the C language. Macros can be used to generate inline code that takes the place of a function call. Their use can reduce program execution time. The chapter presents a detailed discussion of the preprocessor, including new features added by the ANSI committee. In traditional C, the preprocessor varies considerably from one compiler to another. In ANSI C, the functionality of the preprocessor has been completely specified.
　　Recursion and List Processing. Chapter 5, "Functions," has a careful discussion of recursion, which is often a mystifying topic for the beginner. The use of recursion is illustrated again in Chapter 8, "The Preprocessor," with the quicksort algorithm and in Chapter 10, "Structures and List Processing," with basic list processing techniques. A thorough knowledge of list processing techniques is necessary in advanced programming and data structure courses.
　　Operating System Connection. Chapter 11, "Input/Output and the Operating System,"makes the operating system connection. In this chapter, we explain how to do file processing and discuss at length the various input/output functions in the standard library. We also explain how to execute a system command from within a C program and how to set file permissions and use of environment variables. We give explicit examples showing the use of the profiler, the librarian, and the make facility.
.　　Advanced Applications. We discuss a number of advanced applications in Chapter 12,"Advanced Applications." We present topics such as creating concurrent processes,overlaying a process, interprocess communication, and signals, along with working code. Also, we discuss the dynamic allocation of vectors and matrices for engineers and scientists. These advanced topics can be used selectively according to the needs of the audience: They could form the basis for an excellent second course in programming practice. This book can be used, too, as an auxihary text in advanced computer science courses that employ C as their implementation language.Tables, Summaries, and Exercises. Throughout the book are many tables and lists that succinctly summarize key ideas. These tables aid and test language comprehension. For example, C is very rich in operators and allows almost any useful combination of operator mix. It is essential to understand order of evaluation and association of each of these operators separately and in combination. These points are illustrated in tables throughout the text. As a reference tool, the tables and code are easily looked up.
　　 The exercises test elementary features of the language and discuss advanced and system-dependent features. Many exercises are oriented to problem solving, others test the reader's syntactic or Semantic understanding of C. Some exercises include a tutorial discussion that is tangential to the text but may be of special interest to certain readers.The exercises offer the instructor all levels of question, so as to allow assignments suitable to the audience.