C语言经典入门指南：必读书籍与核心概念

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本资源是一份关于C语言的经典教程书籍概览，旨在为学习C语言的读者提供全面的基础知识。它分为四个主要章节，涵盖了C语言的入门、类型、控制流和函数编程结构。首先，在" Preface"和" Preface to the first edition"中，作者可能介绍了本书的定位、目标读者以及对C语言初学者的适用性。这些部分通常会强调C语言在IT行业的重要性，以及为何选择这本书作为学习资源。第一章是" A Tutorial Introduction"，从实际操作开始，引导读者入门。这部分包括： 1.1 "Getting Started"：介绍如何设置开发环境，理解C语言的基本概念。 1.2 "Variables and Arithmetic Expressions"：讲解变量的定义和使用，以及基本的算术运算。 1.3 "The for statement"：解释循环结构，这是控制程序流程的关键部分。 1.4 "Symbolic Constants"：讨论符号常量的作用，方便代码中的数值表示。 1.5 "Character Input and Output"：涉及字符输入输出，如文件复制、字符计数、行数计数和单词计数等实用功能。 1.6 "Arrays"：介绍数组的概念，以及它们在存储和处理数据时的优势。 1.7 "Functions"：讲解函数的定义与调用，包括参数传递方式（call by value）。 1.8 "Character Arrays"：深入探讨字符数组的应用。 1.9 "External Variables and Scope"：讲解全局变量和局部变量的作用域规则。第二章关注的是类型、运算符和表达式，内容涵盖： 2.1 "Variable Names"：命名规则和最佳实践。 2.2 "Data Types and Sizes"：介绍C语言的数据类型及其内存占用。 2.3 "Constants"：详细说明常量的定义和类型。 2.4 "Declarations"：声明变量的方式和注意事项。 2.5 "Arithmetic Operators"：各种算术运算符的使用。 2.6 "Relational and Logical Operators"：比较和逻辑运算的用法。 2.7 "Type Conversions"：不同类型之间的转换规则。 2.8 "Increment and Decrement Operators"：自增和自减运算符的使用。 2.9 "Bitwise Operators"：位操作符，对于底层编程有重要作用。 2.10 "Assignment Operators and Expressions"：赋值操作符和复合表达式。 2.11 "Conditional Expressions"：条件语句的实现。 2.12 "Precedence and Order of Evaluation"：运算符的优先级和求值顺序。第三章深入探讨控制流程，包括： 3.1 "Statements and Blocks"：语句和块的概念，以及它们在控制程序流程中的作用。 3.2 "If-Else"：条件判断结构。 3.3 "Else-If"：嵌套的条件结构。 3.4 "Switch"：switch-case结构，用于多选项的选择。 3.5 "Loops - While and For"：循环结构，包括while和for循环。 3.6 "Loops - Do-While"：do-while循环，强调先执行后判断。 3.7 "Break and Continue"：控制循环流程的中断和跳过当前迭代。 3.8 "Goto and labels"：虽然在现代C语言中较少使用，但这里也会提及这两种古老的控制结构。最后一章"Functions and Program Structure"，重点在于： - 函数的设计和组织，包括参数传递和返回值。 - 程序结构的构建，如模块化和良好的代码组织原则。通过这些章节，读者可以系统地学习C语言的基础知识，逐步掌握编程技能，为后续的高级主题和技术打下坚实基础。这本书是C语言学习者的宝贵资源，值得投入时间和精力去深入研究和实践。

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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