《The Art and Science of C》电子版：一份图书馆基础计算机科学导论

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"《The Art and Science of C》是一本基于图书馆的计算机科学入门书籍，旨在教授C语言的精髓和理论。作者通过清晰的写作方式纪念Grace E. Bloom，并分享了电子版的制作初衷和背后的故事。这本书由ADDISON WESLEY出版社在1994年出版，共704页，价格较高。内容涵盖C语言的深入学习，对初学者来说具有一定的挑战性。电子版的制作目的是让更多人有机会接触到这本书，同时提高其知名度。书中还包含了作者对于教学内容的反思，以及自己在编程学习路径上的选择，如JavaScript、VBScript、MATLAB和Mathematica等技术的比较和学习经历。" 在《The Art and Science of C》中，读者将深入理解C语言的艺术与科学，这不仅包括语法和编程技巧，还涵盖了计算机科学的基础概念。C语言作为一门强大的系统级编程语言，它的学习需要对内存管理、指针、数据结构、函数、预处理器等有深刻的理解。这本书通过实例和理论相结合的方式，帮助读者建立起扎实的C语言基础。书中提到的图书馆背景，暗示了它注重理论与实践的结合，可能包含了一系列的练习题和项目，鼓励读者动手实现以巩固所学知识。此外，作者提及在教学过程中对传统课程的不满，反映出这本书可能强调创新和实用性，鼓励读者超越课本，将所学应用到实际问题中。在作者个人的学习历程中，JavaScript的引入揭示了本书不仅限于C语言，还可能讨论到Web开发的相关技术，如客户端脚本编程。而VBScript、MATLAB和Mathematica的提及，表明书中可能涉及到了多种编程语言和工具的对比，帮助读者根据自己的需求和兴趣做出选择。《The Art and Science of C》不仅仅是一本C语言教程，更是一本引导读者探索计算机科学的综合教材，它结合了理论与实践，传统与创新，旨在培养全面的编程思维和技能。无论是对初学者还是有一定经验的程序员，这本书都能提供有价值的学习资源和启示。

1-2 What is computer science?

Growing up in the modern world has probably given you some idea of what a

computer is. This text, however, is less concerned with computers as physical devices

than with computer science. At first glace, the words computer and science seem an

incongruous pair. In its classical usage, science refers to the study of natural

phenomena; when people talk about biological science or physical science, we

understand and feel comfortable with that usage. Computer science doesn’t seem the

same sort of thing. The fact that computers are human-made artifacts makes us reticent

to classify the study of computers as a science. After all, modern technology has also

produced cars, but we don’t talk about “car science.” Instead, we refer to “automotive

engineering” or “automobile technology.” Why should computers be any different?

To answer this question, it is important to recognize that the computer itself is

only part of the story. The physical machine that you can buy today at your local

computer store is an example of computer hardware. It is tangible. You can pick it up,

take it home, and put it on your desk. If need be, you could use it as a doorstop, albeit a

rather expensive one. But if there were nothing there besides the hardware, if a

machine came to you exactly as it rolled off the assemble line, serving as a doorstop

would be one of the few jobs it could do. A modern computer is a general-purpose

machine, with the potential to perform a wide variety of tasks. To achieve that potential,

however, the computer must be programmed. The act of programming a computer

consists of providing it with a set of instructions—a program—that specifies all the

steps necessary to solve the problem to which it is assigned. These programs are

generically known as software, and it is the software, together with the hardware, that

makes computation possible.

In contrast to hardware, software is an abstract, intangible entity. It is a sequence

of simple steps and operations, stated in a precise language that the hardware can

interpret. When we talk about computer science, we are concerned primarily with the

domain of computer software and, more importantly, with the even more abstract

domain of problem solving. Problem solving turns out to be a highly challenging

activity that requires creativity, skill, and discipline. For the most part, computer

science is best thought of as the science of problem solving in which the solutions

happen to involve a computer.

This is not to say that the computer itself is unimportant. Before computers,

people could solve only relatively simple computational problems. Over the last 50

years, the existence of computers has made it possible to solve increasingly difficult

and sophisticated problems in a timely and cost-effective way. As the problems we

attempt to solve become more complex, so does the task of finding effective solution

techniques. The science of problem solving has thus been forced to advance along with

the technology of computing.

CPU

Secondary

storage

I/O devices

memory

Figure 1-1

1-3 A brief tour of computer hardware

This text focuses almost exclusively on software and the activity of solving

problems by computer that is the essence of computer science. Even so, it is important

to spend some time in this chapter talking about the structure of computer hardware at

a very general level of detail. The reason is simple. Programming is a learn-by-doing

discipline. You will not become a programmer just by reading this book, even if you

solve all the exercises on paper. Learning to program is hands-on work and requires

you to use a computer.

In order to use a computer, you need to become acquainted with its hardware. You

have to know how to turn the computer on, how to use the keyboard to type in a

program, and how to execute that program once you’ve written it. Unfortunately, the

steps you must follow in order to perform these operations differ significantly from one

computer system to another. As someone who is writing a general textbook, I cannot

tell you how your own particular system works and must instead concentrate on

general principles that are common to any computer you might be using. As you read

this section, you should look at the computer you have and see how the general

discussion applies to that machine.

Most computer systems today consist of the components shown in Figure 1-1.

Each of the components in the diagram is connected by a communication channel

called a bus, which allows data to flow between the separate units. The individual

components are described in the sections that follow.

The CPU

The central processing unit or CPU is the “brain” of the computer. It performs

the actual computation and controls the activity of the entire computer. The actions of

the CPU are determined by a program consisting of a sequence of coded instructions

stored in the memory system. One instruction, for example, might direct the computer

to add a pair of numbers. Another might make a character appear on the computer

screen. By executing the appropriate sequence of simple instructions, the computer can

be made to perform complex tasks.

In a modern computer, the CPU consists of an integrated circuit—a tine chip of

silicon that has been imprinted with millions of microscopic transistors connected to

form larger circuits capable of carrying out simple arithmetic and logical operations.

Memory

When a computer executes a program, it must have some way to store both the

program itself and the data involved in the computation. In general, any piece of

computer hardware capable of storing and retrieving information is a storage device.

The storage devices that are used while a program is actively running constitute its

primary storage, which is more often called its memory. Since John von Neumann

first suggested the idea in 1946, computers have used the dame memory to store both

the individual instructions that compose the program and the data used during

computation.

Memory systems are engineered to be very efficient so that they can provide the

CPU with extremely fast access to their contents. In today’s computers, memory is

usually built out of a special integrated-circuit chip called a RAM, which stands for

random-access memory. Random-access memory allows the program to use the

contents of any memory cell at any time. Chapter 11 discusses the structure of the

memory system in more detail.

Secondary storage

Although computers usually keep active data in memory whenever a program is

running, most primary storage devices have the disadvantage that they function only

when the computer is turned on. When you turn off your compute, any information that

was stored in primary memory is lost. To store permanent data, you need to use a

storage device that does not require electrical power to maintain its information. Such

devices constitute secondary storage.

The most common secondary storage devices used in computers today are disks,

which consist of circular spinning platters coated with magnetic material used to record

data. In a modern personal computer, disks come in two forms: hard disks, which are

built into the computer system, and floppy disks, which are removable. When you

compose and edit your program, you will usually do so on a hard disk, if one is

available. When you want to move the program to another computer or make a backup

copy for safekeeping, you will typically transfer the program to a floppy disk.

I/O devices

For the computer to be useful, it must have some way to communicate with users

in the outside world. Computer input usually consists of characters typed on a

keyboard. Output from the computer typically appears on the computer screen or on a

printer. Collectively, hardware devices that perform input and output operations are

called I/O devices, where I/O stands for input/output.

I/O devices vary significantly from machine to machine. Outside of the standard

Alphabetic keys, computer keyboards have different arrangements and even use

different names for some of the important keys. For example, the key used to indicate

the end of a line is labeled Return on some keyboards and Enter on others. On some

computer systems, you make changes to a program by using special function keys on

the top or side of the keyboard that provide simple editing operations. On other systems,

you can accomplish the same task by using a hand-held pointing device called a mouse

to select program text that you wish to change. In either case, the computer keeps track

of the current typing position, which is usually indicated on the screen by flash line or

rectangle called the cursor.

In this text, computer input and output are illustrated using an inset box with

rounded corners. In most cases, the contents of the box indicate what appears on the

screen when you execute your program and is called a sample run. For example, the

following sample run illustrates what will appear on the screen after you execute the

add

Input from the user is shown in color to distinguish it from the out generated by

the program. To make the use actions more clear, the diagram also uses the symbol  to

indicate that the user has pressed the Return or Enter key, signifying the end of the

input line, although this symbol does not actually appear on the screen.

1-4 Algorithms

Now that you have a sense of the basic structure of a computer system, let’s turn

to computer science. Because computer science is the discipline of solving problems

with the assistance of a computer, you need to understand a concept that is fundamental

to both computer science and the abstract discipline of problem solving the concept of

This program adds two numbers.

number? 2

The total is 4.

and algorithm

. Informally, you can think of an algorithm as a strategy for solving a

problem. To appreciate how computer scientists use the term, however, it is necessary

to formalize that intuitive understanding and tighten up the definition.

To be an algorithm, a solution technique must fulfill three basic requirements.

First of all, an algorithm must be presented in a clear, unambiguous form so that it is

possible to understand what steps are involved. Second, the steps within an algorithm

must be effective, in the sense that it is possible to carry them out in practice. A

technique, for example, that includes the operation “multiply r by the exact value of

п” is not effective, since it is not possible to compute the exact value ofп.Third, an

algorithm must not run on forever but must deliver its answer in a finite amount of time.

In summary, an algorithm must be

1. Clearly and unambiguously defined

2. Effective, in the sense that its steps are executable.

3. Finite, in the sense that it terminates after a bounded number of steps.

These properties will turn out to be more important later on when you begin to

work with complex algorithms. For the moment, it is sufficient to think of algorithms

as abstract solution strategies—strategies that will eventually become the core of the

programs you write.

As you will soon discover, algorithms—like the problems they are intended to

solve — vary significantly in complexity. Some problems are so simple that an

appropriate algorithm springs immediately to mind, and you can write the programs to

solve such problems without too much trouble. As the problems become more complex,

however, the algorithms needed to solve them begin to require more thought. In most

cases, several different algorithms are available to solve a particular problem, and you

need to consider a variety of potential solution techniques before writing the final

program. You will have a chance to revisit this topic in Chapter 6, which addresses how

to decide which algorithm is best for a given problem.

1-5 Programming languages and compilation

Solving a problem by computer consists of two conceptually distinct steps. First,

you need to develop an algorithm, or choose an existing one, that solves the problem.

This part of the process is called algorithmic design. The second step is to express that

algorithm as a computer program in a program in a programming language. This

process is called coding.

As you begin to learn about programming, the process of coding—translating

your algorithm into a functioning C program—will seem to be the more difficult phase

of the process. As a new programmer, you will, after all, be starting with simple

problems just as you would when learning any new skill. Simple problems tend to have

simple solutions, and the algorithmic design phase will not seem particularly

challenging. Because the language and its rules are entirely new and unfamiliar,

however, coding may at times seem difficult and arbitrary. I hope it is reassuring to say

that coding will rapidly become easier as you learn more about the programming

process. At the same time, however, algorithmic design will get harder as the problems

you are asked to solve increase in complexity.

When new algorithms are introduced in this text, they will usually be expressed

initially in English. Although it is offer less precise than one would like, English is a

reasonable language in which to express solution strategies as long as the

communication is entirely between people who speak English. Obviously, if you

wanted to resent your algorithm to someone who spoke only Russian, English would

The word algorithm comes to use from the name of the ninth-century Arabic mathematician

Abu Ja’far Mohammed ibn Mûsâ al –Knowârizmî, who wrote a treatise on mathematics entitled

Kitab al jabr w’almuqabala (which itself gave rise to the English word algebra).

no longer be an appropriate choice. English is likewise an inappropriate choice for

presenting an algorithm to a computer. Although computer scientists have been

working on this problem for decades, understanding English or Russian or any other

human language continues to lie beyond the boundaries of current technology. The

computer would be completely unable to interpret your algorithm if it were expressed

in human language. To make an algorithm accessible to the computer, you need to

translate it into a programming language. There are many programming languages in

the world, including Fortran, BASIC, Pascal, Lisp, and a host of others. In this text,

you will learn how to use the programming language C—the language that has become

the de facto standard in the computing industry over the last several years.

The programming languages listed above, including C, are examples of what

computer scientists call higher-level languages. Such languages are designed to be

independent of the particular characteristics that differentiate computers and to work

instead with general algorithmic concepts that can be implemented on any computer

system. Internally, each computer system understands a low-level language that is

specific to that type of hardware. For example, the Apple Macintosh computer and the

IBM PC use different underlying machine languages, even though both of them can

execute programs written in a higher-level language such as C.

To make it possible for a program written in a higher-level language to run on

different computer systems, the program must first be translated into the low-level

machine language appropriate to the computer on which the program will run. For

example, if you are writing C programs for a Macintosh, you will need to run a special

program that translates C into machine language for the Macintosh. If you are using the

IBM PC to run the same program, you need to use a different translator. Programs that

perform the translation between a higher-level language and machine language are

called compilers.

Before you can run a program on most computer systems, it is necessary to enter

the text of the program and store it in a file, which is the generic name for any

collection of information stored in the computer’s secondary storage. Every file must

have a name, which is usually divided into two parts separated by a period, as in

myprog.c. When you create a file, you choose the root name, which is the part of the

name preceding the period, and use it to tell yourself what the file contains. The portion

of the filename following the period indicates what the file is used for and is called the

extension. Certain extensions have preassigned meanings. For example, the

extension .c indicates a program fie written in the C language. A file containing

program text is called a source file.

The general process of entering or changing the contents of a file is called editing

that file. The editing process differs significantly between individual computer systems,

so it is not possible to describe it in a way that works for every type of hardware. When

you work on a particular computer system, you will need to learn how to create new

files and to edit existing ones. You can find this information in the computer manual or

the documentation fro the C compiler you are using.

010001001000100

111000100011010

101010101100100

010001001110001

000110101010101

101101010101010

001100101001000

101001101101010

101010101010110

101101010110101

010101010101111

010101100010010

010110101010110

011011110001001

001011010101010

101010101111000

linker

source files object files

other object

fileggs/librarie

executable files

Figure 1-2

#include <stdio.h>

main()

{

printf(“hello”);

}

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