C语言之父经典：《C Programming Language》英文版解读

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"C语言程序设计语言（英文版）是由C语言之父丹尼斯·里奇与布莱恩·柯林汉合著的经典教程，首次出版于1988年，对于学习C语言的读者来说是一本极具价值的参考书。书中涵盖了C语言的基础知识和编程实践，旨在引导读者逐步掌握这一强大的编程工具。" 正文: 这本书分为多个章节，逐步深入地介绍了C语言的核心概念和语法。首先，"Chapter1: A Tutorial Introduction"作为入门章节，讲解了如何开始编写C程序，包括变量、算术表达式、for循环、符号常量以及基本的输入输出操作。通过几个简单的示例程序，如文件复制、字符计数、行计数和词计数，帮助初学者理解C语言的基本结构和功能。接着，"Chapter2: Types, Operators and Expressions"深入探讨了C语言中的类型系统、运算符和表达式。这一章详细阐述了变量命名规则、数据类型及其大小、常量定义、声明语法、算术运算符（如加减乘除）、关系和逻辑运算符、类型转换、增量和减量运算符、位运算符、赋值运算符、条件表达式以及运算符的优先级和求值顺序。这些都是编程时处理数据和控制程序流程的基础。在"Chapter3: Control Flow"中，作者介绍了程序控制流的关键元素，如语句和结构，包括条件语句（if-else）、开关语句（switch）、循环结构（while和do-while）、跳转语句（break和continue），以及如何使用嵌套结构来构建复杂的逻辑流程。这些内容是编写控制程序执行路径的关键。后续章节会继续涵盖函数、数组、指针、结构体、联合、枚举、预处理器、内存管理、错误处理等更高级的主题，这些都是C语言强大且灵活特性的体现。通过这些章节的学习，读者将能够编写出高效、灵活的C程序，并对程序的底层工作有更深入的理解。《C语言程序设计语言》是一本全面而权威的教程，适合初学者和有经验的程序员作为参考。丹尼斯·里奇和布莱恩·柯林汉的清晰表述和精心设计的实例使得复杂概念易于理解和应用，为读者提供了扎实的C语言基础。

Chapter 1 - A Tutorial Introduction

to print this sequence of characters

} \n represents the newline character

The first C program

The statements of a function are enclosed in braces { }. The function main contains only one statement,

printf("hello, world\n");

A function is called by naming it, followed by a parenthesized list of arguments, so this calls the function printf

with the argument "hello, world\n". printf is a library function that prints output, in this case the string

of characters between the quotes.

A sequence of characters in double quotes, like "hello, world\n", is called a character string or string

constant. For the moment our only use of character strings will be as arguments for printf and other functions.

The sequence \n in the string is C notation for the newline character, which when printed advances the output to

the left margin on the next line. If you leave out the \n (a worthwhile experiment), you will find that there is no

line advance after the output is printed. You must use \n to include a newline character in the printf argument;

if you try something like

printf("hello, world

");

the C compiler will produce an error message.

printf never supplies a newline character automatically, so several calls may be used to build up an output line

in stages. Our first program could just as well have been written

#include <stdio.h>

main()

{

printf("hello, ");

printf("world");

printf("\n");

}

to produce identical output.

Notice that \n represents only a single character. An escape sequence like \n provides a general and extensible

mechanism for representing hard-to-type or invisible characters. Among the others that C provides are \t for tab,

\b for backspace, \" for the double quote and \\ for the backslash itself. There is a complete list in

Section 2.3.

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Chapter 1 - A Tutorial Introduction

which set the variables to their initial values. Individual statements are terminated by semicolons.

Each line of the table is computed the same way, so we use a loop that repeats once per output line; this is the

purpose of the while loop

while (fahr <= upper) {

...

}

The while loop operates as follows: The condition in parentheses is tested. If it is true (fahr is less than or equal

to upper), the body of the loop (the three statements enclosed in braces) is executed. Then the condition is re-

tested, and if true, the body is executed again. When the test becomes false (fahr exceeds upper) the loop ends,

and execution continues at the statement that follows the loop. There are no further statements in this program, so

it terminates.

The body of a while can be one or more statements enclosed in braces, as in the temperature converter, or a

single statement without braces, as in

while (i < j)

i = 2 * i;

In either case, we will always indent the statements controlled by the while by one tab stop (which we have

shown as four spaces) so you can see at a glance which statements are inside the loop. The indentation emphasizes

the logical structure of the program. Although C compilers do not care about how a program looks, proper

indentation and spacing are critical in making programs easy for people to read. We recommend writing only one

statement per line, and using blanks around operators to clarify grouping. The position of braces is less important,

although people hold passionate beliefs. We have chosen one of several popular styles. Pick a style that suits you,

then use it consistently.

Most of the work gets done in the body of the loop. The Celsius temperature is computed and assigned to the

variable celsius by the statement

celsius = 5 * (fahr-32) / 9;

The reason for multiplying by 5 and dividing by 9 instead of just multiplying by 5/9 is that in C, as in many other

languages, integer division truncates: any fractional part is discarded. Since 5 and 9 are integers. 5/9 would be

truncated to zero and so all the Celsius temperatures would be reported as zero.

This example also shows a bit more of how printf works. printf is a general-purpose output formatting

function, which we will describe in detail in

Chapter 7. Its first argument is a string of characters to be printed,

with each % indicating where one of the other (second, third, ...) arguments is to be substituted, and in what form it

is to be printed. For instance, %d specifies an integer argument, so the statement

printf("%d\t%d\n", fahr, celsius);

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Chapter 1 - A Tutorial Introduction

causes the values of the two integers fahr and celsius to be printed, with a tab (\t) between them.

Each % construction in the first argument of printf is paired with the corresponding second argument, third

argument, etc.; they must match up properly by number and type, or you will get wrong answers.

By the way, printf is not part of the C language; there is no input or output defined in C itself. printf is just a

useful function from the standard library of functions that are normally accessible to C programs. The behaviour of

printf is defined in the ANSI standard, however, so its properties should be the same with any compiler and

library that conforms to the standard.

In order to concentrate on C itself, we don't talk much about input and output until

chapter 7. In particular, we will

defer formatted input until then. If you have to input numbers, read the discussion of the function scanf in

Section 7.4. scanf is like printf, except that it reads input instead of writing output.

There are a couple of problems with the temperature conversion program. The simpler one is that the output isn't

very pretty because the numbers are not right-justified. That's easy to fix; if we augment each %d in the printf

statement with a width, the numbers printed will be right-justified in their fields. For instance, we might say

printf("%3d %6d\n", fahr, celsius);

to print the first number of each line in a field three digits wide, and the second in a field six digits wide, like this:

0 -17

20 -6

40 4

60 15

80 26

100 37

...

The more serious problem is that because we have used integer arithmetic, the Celsius temperatures are not very

accurate; for instance, 0

F is actually about -17.8

C, not -17. To get more accurate answers, we should use floating-

point arithmetic instead of integer. This requires some changes in the program. Here is the second version:

#include <stdio.h>

/* print Fahrenheit-Celsius table

for fahr = 0, 20, ..., 300; floating-point version */

main()

{

float fahr, celsius;

float lower, upper, step;

lower = 0; /* lower limit of temperatuire scale */

upper = 300; /* upper limit */

step = 20; /* step size */

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