preface

书名:C语言科学与艺术,以前交钱下载的

ABOUT THE AUTHOR

I first began teaching introductory computer science more than 20 years
ago while I was still a student at Harvard.  Since receiving my Ph.D. in
1980, I have taught computer science at Harvard, Wellesley, and
Stanford, where I am Associate Chair of the Computer Science Department.
In that capacity, I am responsible for the undergraduate program in
computer science.  Although I have taught advanced courses in computer
science and have also worked in the research industry, my greatest joy
comes from opening up the enormous power of computers to students who
are just beginning to learn about them.  In their excitement, my own
love for computer science is constantly renewed.

In addition to my teaching at Stanford, I have served since 1990 as the
president of Computer Professionals for Social Responsibility, a
public-interest association of computer professionals with 2000 members
in 22 chapters throughout the United States.  Computers affect our
society in many different ways.  Just as it is important to learn about
the technology, it is critical that we also take the responsibility to
ensure that computers are used for the benefit of all. If you have
suggestions as to how I might make the presentation more clear, or you
encounter errors in this text, please let me know. You can reach me by
electronic mail at [e-mail].

Eric S. Roberts
Stanford University


TO THE STUDENT

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 calculations 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 medical technology.

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.  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 necessary
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 have 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.


TO THE INSTRUCTOR

In 1991-92, Stanford decided to restructure its introductory computer
science curriculum to use ANSI C instead of Pascal.  We chose to adopt
ANSI C in our introductory courses for the following reasons:

   o  Students demanded a more practical language.  Future employers
      want students to have more direct experience with the tools
      industry uses, which today are principally C and C++.  With
      few employment opportunities listed for Pascal programmers in
      the newspaper employment section, our students began to
      question the relevance of their education.

   o  Our Pascal-based curriculum taught students to program in a
      language that they would never again use.  We discovered that
      many of those students, when they abandoned Pascal for more
      modern languages, often forgot everything they had learned
      about programming style and the discipline of software
      engineering.  Having now taught these skills in the context of
      a language that the students continue to use, we have found
      that they end up writing much better programs.

   o  Many of our advanced computer science courses, particularly in
      the systems area, require students to program in C.  Working
      with C from the beginning gives students much more experience
      by the time they reach the advanced courses.

   o  Learning C early paves the way to learning C++ and the
      object-oriented paradigm.  Because our students have a strong
      background in C programming after their first year of study,
      we have been able to offer our course on object-oriented
      system design much earlier in the curriculum.

   o  C makes it possible to cover several important topics, such as
      modular development and abstract data types, that are hard to
      teach in a Pascal environment.

   o  In the last five years, C has made significant headway toward
      replacing Fortran as the lingua franca of programming for the
      engineering sciences.

Given our experience over the last two years, I am convinced that the
choice was a good one and that our program is stronger because of the
change.

At the same time, it is important to recognize that teaching C in the
first programming course is not always easy.  C was designed for
programmers, not introductory students.  Many of its features make sense
only when understood in terms of a larger conceptual framework that new
students do not recognize.  In many respects, C is a complex language.
To teach it at the introductory level, we must find a way to control its
complexity.

THE LIBRARY-BASED APPROACH

One of the central goals of this text is to enable teachers to manage
C's inherent complexity.  Managing complexity, however, is precisely
what we do as program- mers.  When we are faced with a problem that is
too complex for immediate solution, we divide it into smaller pieces and
consider each one independently.  Moreover, when the complexity of one
of those pieces crosses a certain threshold, it makes sense to isolate
that complexity by defining a separate abstraction that has a simple
interface.  The interface protects clients from the underlying details
of the abstraction, thereby simplifying the conceptual structure.

The same approach works for teaching programming.  To make the material
easier for students to learn, this text adopts a library-based approach
that emphasizes the principle of abstraction.  The essential character