C编程语言(英文第2版)教程

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"C程序设计语言(英文第2版)" 是一本经典的编程教材，由Prentice Hall出版，作者深入浅出地介绍了C语言的基础知识。本书的第二版提供了对C语言更全面和深入的讲解。在书中，作者首先通过一个简短的前言介绍了第一版的背景，并正式开启教程介绍。第一章“ATutorialIntroduction”旨在引导初学者入门，从以下几个方面展开： 1.1 Getting Started：这部分教读者如何开始编写和运行C程序，包括环境设置和基本的编程步骤。 1.2 Variables and Arithmetic Expressions：讲解变量的概念和算术表达式的用法，这是所有编程语言的基础。 1.3 The for statement：介绍C语言中的for循环，这是控制程序流程的重要工具。 1.4 Symbolic Constants：讲解符号常量的使用，提高代码的可读性。 1.5 Character Input and Output：涵盖了字符输入输出，包括文件复制、字符计数、行计数和单词计数等实用示例。 1.6 Arrays：讨论数组，让读者理解如何存储和处理一组数据。 1.7 Functions：介绍函数的定义与调用，函数是组织代码和复用逻辑的关键。 1.8 Arguments - Call by Value：解释参数传递机制，即按值传递。 1.9 Character Arrays：进一步探讨字符数组，特别是字符串的处理。 1.10 External Variables and Scope：讨论外部变量和作用域，这对于管理全局变量和理解代码结构至关重要。第二章“Types, Operators and Expressions”详细介绍了C语言的数据类型、运算符和表达式： 2.1 Variable Names：规定了变量命名的规则。 2.2 Data Types and Sizes：讲解各种数据类型（如int、float、char等）及其内存占用。 2.3 Constants：介绍了常量的定义和使用。 2.4 Declarations：讨论声明语句，用于定义变量和数据类型。 2.5 Arithmetic Operators：涵盖了加减乘除等基本算术运算符。 2.6 Relational and Logical Operators：讲解关系和逻辑运算符，用于比较和逻辑判断。 2.7 Type Conversions：讨论类型转换，允许不同类型的值相互操作。 2.8 Increment and Decrement Operators：介绍了递增和递减运算符，它们在循环和计算中非常常见。 2.9 Bitwise Operators：讲解位运算符，用于处理二进制数据。 2.10 Assignment Operators and Expressions：涵盖了赋值运算符以及使用它们的表达式。 2.11 Conditional Expressions：介绍条件运算符，实现三元逻辑。 2.12 Precedence and Order of Evaluation：讨论运算符的优先级和求值顺序，这对于正确理解表达式的结果至关重要。第三章“Control Flow”讲解了控制程序执行流程的语句： 3.1 Statements and Blocks：介绍语句和代码块的概念，使程序结构更清晰。 3.2 If-Else：讲解if和else语句，实现条件分支。 3.3 Else-If：引入else-if，扩展了条件判断的灵活性。 3.4 Switch：介绍了switch语句，提供了一种多分支选择的结构。 3.5 Loops - While and For：讨论while和for循环，实现重复执行的逻辑。 3.6 Loops - Do-While：介绍了do-while循环，确保至少执行一次循环体。 3.7 Break and Continue：讲解break和continue语句，用于提前结束循环或跳过循环体的一部分。 3.8 Goto and labels：虽然不推荐，但仍然提到了goto语句和标签，作为控制流程的手段。第四章“Functions and Program Structure”继续深入，讲述函数和程序结构，帮助读者构建更复杂的程序。这本经典教材不仅适合初学者，也对有经验的程序员有价值，因为它深入剖析了C语言的细节，有助于读者理解和掌握这一强大而灵活的编程语言。

Width and precision may be omitted from a specification: %6f says that the number is to be at

least six characters wide; %.2f specifies two characters after the decimal point, but the width

is not constrained; and %f merely says to print the number as floating point.

print as decimal integer

%6d

print as decimal integer, at least 6 characters wide

print as floating point

%6f

print as floating point, at least 6 characters wide

%.2f

print as floating point, 2 characters after decimal point

%6.2f

print as floating point, at least 6 wide and 2 after decimal point

Among others, printf also recognizes %o for octal, %x for hexadecimal, %c for character, %s

for character string and %% for itself.

Exercise 1-3. Modify the temperature conversion program to print a heading above the table.

Exercise 1-4. Write a program to print the corresponding Celsius to Fahrenheit table.

1.3 The for statement

There are plenty of different ways to write a program for a particular task. Let's try a variation

on the temperature converter.

#include <stdio.h>

/* print Fahrenheit-Celsius table */

main()

{

int fahr;

for (fahr = 0; fahr <= 300; fahr = fahr + 20)

printf("%3d %6.1f\n", fahr, (5.0/9.0)*(fahr-32));

}

This produces the same answers, but it certainly looks different. One major change is the

elimination of most of the variables; only fahr remains, and we have made it an int. The

lower and upper limits and the step size appear only as constants in the for statement, itself a

new construction, and the expression that computes the Celsius temperature now appears as

the third argument of

printf instead of a separate assignment statement.

This last change is an instance of a general rule - in any context where it is permissible to use

the value of some type, you can use a more complicated expression of that type. Since the

third argument of

printf must be a floating-point value to match the %6.1f, any floating-

point expression can occur here.

The for statement is a loop, a generalization of the while. If you compare it to the earlier

while, its operation should be clear. Within the parentheses, there are three parts, separated

by semicolons. The first part, the initialization

fahr = 0

is done once, before the loop proper is entered. The second part is the

test or condition that controls the loop:

fahr <= 300

This condition is evaluated; if it is true, the body of the loop (here a single ptintf) is

executed. Then the increment step

fahr = fahr + 20

is executed, and the condition re-evaluated. The loop terminates if the condition has become

false. As with the while, the body of the loop can be a single statement or a group of

statements enclosed in braces. The initialization, condition and increment can be any

expressions.

The choice between

while and for is arbitrary, based on which seems clearer. The for is

usually appropriate for loops in which the initialization and increment are single statements

and logically related, since it is more compact than while and it keeps the loop control

statements together in one place.

Exercise 1-5. Modify the temperature conversion program to print the table in reverse order,

that is, from 300 degrees to 0.

1.4 Symbolic Constants

A final observation before we leave temperature conversion forever. It's bad practice to bury

``magic numbers'' like 300 and 20 in a program; they convey little information to someone

who might have to read the program later, and they are hard to change in a systematic way.

One way to deal with magic numbers is to give them meaningful names. A #define line

defines a symbolic name or symbolic constant to be a particular string of characters:

#define name replacement list

Thereafter, any occurrence of name (not in quotes and not part of another name) will be

replaced by the corresponding replacement text. The name has the same form as a variable

name: a sequence of letters and digits that begins with a letter. The replacement text can be

any sequence of characters; it is not limited to numbers.

#include <stdio.h>

#define LOWER 0 /* lower limit of table */

#define UPPER 300 /* upper limit */

#define STEP 20 /* step size */

/* print Fahrenheit-Celsius table */

main()

{

int fahr;

for (fahr = LOWER; fahr <= UPPER; fahr = fahr + STEP)

printf("%3d %6.1f\n", fahr, (5.0/9.0)*(fahr-32));

}

The quantities LOWER, UPPER and STEP are symbolic constants, not variables, so they do not

appear in declarations. Symbolic constant names are conventionally written in upper case so

they can ber readily distinguished from lower case variable names. Notice that there is no

semicolon at the end of a #define line.

1.5 Character Input and Output

We are going to consider a family of related programs for processing character data. You will

find that many programs are just expanded versions of the prototypes that we discuss here.

The model of input and output supported by the standard library is very simple. Text input or

output, regardless of where it originates or where it goes to, is dealt with as streams of

characters. A text stream is a sequence of characters divided into lines; each line consists of

zero or more characters followed by a newline character. It is the responsibility of the library

to make each input or output stream confirm this model; the C programmer using the library

need not worry about how lines are represented outside the program.

The standard library provides several functions for reading or writing one character at a time,

of which

getchar and putchar are the simplest. Each time it is called, getchar reads the

next input character from a text stream and returns that as its value. That is, after

c = getchar();

the variable c contains the next character of input. The characters normally come from the

keyboard; input from files is discussed in Chapter 7.

The function

putchar prints a character each time it is called:

putchar(c);

prints the contents of the integer variable c as a character, usually on the screen. Calls to

putchar and printf may be interleaved; the output will appear in the order in which the calls

are made.

1.5.1 File Copying

Given getchar and putchar, you can write a surprising amount of useful code without

knowing anything more about input and output. The simplest example is a program that

copies its input to its output one character at a time:

read a character

while (charater is not end-of-file indicator)

output the character just read

read a character

Converting this into C gives:

#include <stdio.h>

/* copy input to output; 1st version */

main()

{

int c;

c = getchar();

while (c != EOF) {

putchar(c);

c = getchar();

}

The relational operator != means ``not equal to''.

What appears to be a character on the keyboard or screen is of course, like everything else,

stored internally just as a bit pattern. The type

char is specifically meant for storing such

character data, but any integer type can be used. We used int for a subtle but important

reason.

The problem is distinguishing the end of input from valid data. The solution is that getchar

returns a distinctive value when there is no more input, a value that cannot be confused with

any real character. This value is called EOF, for ``end of file''. We must declare c to be a type

big enough to hold any value that getchar returns. We can't use char since c must be big

enough to hold EOF in addition to any possible char. Therefore we use int.

EOF is an integer defined in <stdio.h>, but the specific numeric value doesn't matter as long as

it is not the same as any char value. By using the symbolic constant, we are assured that

nothing in the program depends on the specific numeric value.

The program for copying would be written more concisely by experienced C programmers. In

C, any assignment, such as

c = getchar();

is an expression and has a value, which is the value of the left hand side after the assignment.

This means that a assignment can appear as part of a larger expression. If the assignment of a

character to c is put inside the test part of a while loop, the copy program can be written this

way:

#include <stdio.h>

/* copy input to output; 2nd version */

main()

{

int c;

while ((c = getchar()) != EOF)

putchar(c);

}

The while gets a character, assigns it to c, and then tests whether the character was the end-

of-file signal. If it was not, the body of the

while is executed, printing the character. The

while then repeats. When the end of the input is finally reached, the while terminates and so

does

main.

This version centralizes the input - there is now only one reference to getchar - and shrinks

the program. The resulting program is more compact, and, once the idiom is mastered, easier

to read. You'll see this style often. (It's possible to get carried away and create impenetrable

code, however, a tendency that we will try to curb.)

The parentheses around the assignment, within the condition are necessary. The precedence

!= is higher than that of =, which means that in the absence of parentheses the relational

test != would be done before the assignment =. So the statement

c = getchar() != EOF

is equivalent to

c = (getchar() != EOF)

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