C编程语言经典教程：从入门到控制流

5星 · 超过95%的资源需积分: 9 174 浏览量更新于2024-07-18 收藏 791KB PDF 举报

《C Programming Language》是一本由C语言创始人Dennis Ritchie编写的经典英文教材，它全面介绍了C语言的基础知识和高级特性。本书的核心内容围绕C语言的核心概念展开，旨在帮助读者掌握这门编程语言的精髓。在第一部分，作者通过一个简明教程来引导读者入门。第1章“Tutorial Introduction”涵盖了关键主题，如如何开始编写程序（1.1 Getting Started），变量和算术表达式（1.2）的理解与使用，以及循环结构（如for statement，1.3）。此外，还讨论了符号常量（1.4）、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操作，1.5）、数组（1.6）的概念和函数的初步介绍（1.7）。1.8章节讲解了参数传递方式——值传递（Call by Value）和字符数组（1.9），以及外部变量的作用域（1.10）。第二章深入探讨了类型、运算符和表达式。变量名的规则（2.1）、数据类型及其大小（2.2）、常量（2.3）、声明（2.4）和各种算术、关系、逻辑运算符（2.5-2.7）的使用方法被详细阐述。此外，位操作符（2.9）、赋值运算符和表达式（2.10）、条件表达式（2.11）以及运算符优先级和求值顺序（2.12）也是这一章的重点。第三章“Control Flow”涉及控制流程的关键元素。这里介绍了语句和块（3.1）、if-else和else-if结构（3.2-3.3）、switch语句（3.4），以及循环结构——while和for（3.5）、do-while（3.6），并讨论了break和continue语句（3.7）以及goto和标签（3.8）的用法，这些对于理解程序流程控制至关重要。第四章聚焦于函数和程序结构。在这里，基本的函数概念（4.1）以及函数定义、调用和参数传递再次被深入讲解。程序的模块化设计和组织原则也在这一章有所体现，这对于编写复杂程序的组织架构具有指导意义。《C Programming Language》不仅是学习C语言的必备指南，而且是理解和实践计算机科学基础理论的重要资源。无论是初学者还是经验丰富的程序员，都能从中获得丰富的实践经验和理论知识。通过阅读这本书，读者将建立起扎实的C语言基础，为后续的编程生涯打下坚实的基础。

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.

%d print as decimal integer

%6d print as decimal integer, at least 6 characters wide

%f 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

of != 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)

剩余237页未读，继续阅读

vivid_encounter

粉丝: 0
资源: 1

C编程语言经典教程：从入门到控制流

The_C_Programming_Language.pdf

c语言程序设计The.C.Programming.Language(中文版).pdf

The C Programming Language(中文完整版) [C程序设计语言]

C程序设计语言（第2版·新版）__The_C_Programming_Language_Second_c.zip

the_c_programming_language

The_C_programming_Language

The_C_Programming_Language_经典c语言学习教材(含课后习题答案)

The_C_Programming_Language_pdf

The_C_Programming_Language_2nd_edition

The_C_Programming_Language(C语言经典三本书)

最新资源