从零开始学习C语言编程：掌握世界主流语言

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xxi

Preface

This book attempts to teach computer programming to the complete beginner using the C

language. As such, it assumes you have no knowledge whatsoever about programming. And if

you are worried that you are not good at high-school mathematics, don’t be. It is a myth that you

must be good at mathematics to learn programming. In this book, knowledge of primary school

mathematics is all that is required—basic addition, subtraction, multiplication, division, finding

the percentage of some quantity, finding an average or the larger of two quantities.

Some of our most outstanding students over the last thirty years have been people with

little mathematics background from all walks of life—politicians, civil servants, sports people,

housewives, secretaries, clerical assistants, artists, musicians and teachers. On the other hand,

we’ve had mathematical folks who didn’t do as well as might be expected.

What will be an asset is the ability to think logically or to follow a logical argument. If you are

good at presenting convincing arguments, you will probably be a good programmer. Even if you

aren’t, programming is the perfect vehicle for teaching logical thinking skills. You should learn

programming for these skills even if you never intend to become a serious programmer.

The main goal of this book is to teach fundamental programming principles using C, one

of the most widely used programming languages in the world today. C is considered a ‘modern’

language even though its roots date back to the 1970s. Originally, C was designed for writing

‘systems’ programs—things like operating systems, editors, compilers, assemblers and input/

output utility programs. But, today, C is used for writing all kinds of applications programs as

well—word processing programs, spreadsheet programs, database management programs,

accounting programs, games, educational software—the list is endless.

However, this book is more about teaching programming basics than it is about teaching C.

We discuss only those features and statements in C that are necessary to achieve our goal.

Once you learn the principles well, they can be applied to any language.

Chapter 1 gives an overview of the programming process. Chapter 2 describes the basic

building blocks needed to write programs. Chapter 3 explains how to write programs with the

simplest kind of logic—sequence logic. Chapter 4 shows how to write programs which can make

decisions. Chapter 5 explains the notion of ‘looping’ and how to use this powerful programming

idea to solve more interesting problems. Chapter 6 deals with the oft-neglected, but important,

topic of working with characters. Chapter 7 introduces functions—the key concept needed for

writing large programs. Chapter 8 tackles the nemesis of many would-be programmers—array

processing. Chapter 9 explains how lists of items stored in arrays can be searched, sorted and

merged. And Chapter 10 deals with structures—the collection of one or more items, possibly of

different types, grouped together under a single name for convenient handling.

The first step in becoming a good programmer is learning the syntax rules of the

programming language. This is the easy part and many people mistakenly believe that this

makes them a programmer. They get carried away by the cosmetics—they learn the features of a

language without learning how to use them to solve problems.

Chapter 1 ■ elementary programming ConCepts

• To do accounts, we need an accounting program.

• To learn Spanish, we need a program that teaches Spanish.

• To listen to a CD, we need a music-playing program.

• To send a fax, we need a fax-sending program.

• To use the Internet, we need a program called a “Web browser.”

For every task we want to perform, we need an appropriate program. And in order for the

computer to run a program, the program must be stored (we sometimes say loaded) in the

computer’s memory.

But what is the nature of a program? First, we need to know that computers are built to

execute instructions written in what is called machine language. In machine language, everything

is expressed in terms of the binary number system—1s and 0s. Each computer has its own

machine language and the computer can execute instructions written in that language only.

The instructions themselves are very simple: for example, add or subtract two numbers,

compare one number with another, or copy a number from one place to another. How, then, can

the computer perform such a wide variety of tasks, solving such a wide variety of problems, with

such simple instructions?

The answer is that no matter how complex an activity may seem, it can usually be broken

down into a series of simple steps. It is the ability to analyze a complex problem and express

its solution in terms of simple computer instructions that is one of the hallmarks of a good

programmer.

Machine language is considered a low-level programming language. In the early days of

computing (1940s and ‘50s) programmers had to write programs in machine language, that is,

express all their instructions using 1s and 0s.

To make life a little easier for them, assembly language was developed. This was closely

related to machine language but it allowed the programmer to use mnemonic instruction codes

(such as ADD and names for storage locations (such as sum) rather than strings of binary digits

(bits). For instance, a programmer could refer to a number by sum rather than have to remember

that the number was stored in memory location 1000011101101011.

A program called an assembler is used to convert an assembly language program into

machine language. Still, programming this way had several drawbacks:

• It was very tedious and error prone.

• It forced the programmer to think in terms of the machine rather than in

terms of his problem.

• A program written in the machine language of one computer could not

be run on a computer with a different machine language. Changing your

computer could mean having to rewrite all your programs.

To overcome these problems, high-level or problem-oriented languages were developed in

the late 1950s and ‘60s. The most popular of these were FORTRAN (FORmula TRANslation) and

COBOL (COmmon Business-Oriented Language). FORTRAN was designed for solving scientific

and engineering problems that involved a great deal of numerical computation. COBOL was

designed to solve the data-processing problems of the business community.

Chapter 1 ■ elementary programming ConCepts

The idea was to allow the programmer to think about a problem in terms familiar to him

and relevant to the problem rather than have to worry about the machine. So, for instance, if he

wanted to know the larger of two quantities, A and B, he could write

IF A IS GREATER THAN B THEN BIGGER = A ELSE BIGGER = B

rather than have to fiddle with several machine or assembly language instructions to get the same

result. Thus high-level languages enabled the programmer to concentrate on solving the problem

at hand, without the added burden of worrying about the idiosyncrasies of a particular machine.

However, the computer still could only execute instructions written in machine language.

A program called a compiler is used to translate a program written in a high-level language to

machine language.

Thus we speak of a FORTRAN compiler or a COBOL compiler for translating FORTRAN and

COBOL programs, respectively. But that’s not the whole story. Since each computer has its own

machine language, we must have, say, a FORTRAN compiler for a Lenovo ThinkPad computer

and a FORTRAN compiler for a MacBook computer.

1.2 How a Computer Solves a Problem

Solving a problem on a computer involves the following activities:

1. Define the problem.

2. Analyze the problem.

3. Develop an algorithm (a method) for solving the problem.

4. Write the computer program that implements the algorithm.

5. Test and debug (find the errors in) the program.

6. Document the program. (Explain how the program works and

how to use it.)

7. Maintain the program.

There is normally some overlap of these activities. For example, with a large program, a

portion may be written and tested before another portion is written. Also, documentation should

be done at the same time as all the other activities; each activity produces its own items of

documentation that will be part of the final program documentation.

1.2.1 Define the Problem

Suppose we want to help a child work out the areas of squares. This defines a problem to be

solved. However, a brief analysis reveals that the definition is not complete or specific enough

to proceed with developing a program. Talking with the child might reveal that she needs a

program that requests her to enter the length of a side of the square; the program then prints the

area of the square.

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