从入门到精通：《第5版C语言教程》详述

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"《 Beginning C, 5th Edition》是一本专为初学者编写的C语言教材，由业内权威作者倾力打造，适合想要掌握这门广泛使用的编程语言的人群。本书从基础原理出发，通过一步步的实例引导，帮助读者逐步成长为一名熟练的C语言程序员。读者只需备好这本书以及常见的免费或商业C/C++编译器，便能迅速进入实践阶段，编写出自己的C程序。书中详细介绍了C语言的关键概念和技能，包括但不限于： 1. 编程入门 - 章节一引导读者了解编程的基本概念，为后续学习打下坚实的基础。 2. 基础步骤 - 第二章从基础操作开始，如变量声明、数据类型和基本运算，让学习者逐步熟悉编程环境。 3. 决策与控制 - 章节三讨论条件语句（如if-else）和循环结构，使读者能够编写具有逻辑判断的程序。 4. 循环控制 - 第四章深入讲解循环结构，如for和while循环，帮助构建复杂的重复性任务。 5. 数组 - 在第五章中，读者会学习到如何组织和处理数组，这是数据结构的基础。 6. 字符串与文本处理 - 第六章涵盖了字符串操作，这对于处理文本数据至关重要。 7. 指针 - 章节七介绍指针，这是理解C语言内存管理和高级数据操作的关键概念。 8. 程序结构 - 第八章探讨函数和模块化编程，提高代码的复用性和可维护性。 9. 函数深化 - 第九章继续扩展对函数的理解，包括参数传递和返回值。 10. 输入与输出 - 第十章讲解如何接收用户输入并显示结果，涉及格式化输出和标准输入输出流。 11. 数据结构 - 第十一章介绍更复杂的数据结构，如结构体，有助于处理更复杂的数据。 12. 文件操作 - 章节十二涉及文件读写，让程序能够持久存储和交互数据。 13. 预处理器和调试 - 第十三章涵盖了预处理器指令和调试技术，提升程序的质量。 14. 高级主题 - 最后一章探讨了进阶内容，如内存管理、内存泄漏预防等，以及一些特殊用途的编程技巧。此外，书后的附录还提供了额外的技术支持，如计算机算术原理、ASCII字符编码、C语言保留字列表、输入输出格式规范等，帮助读者进一步巩固理论知识并解决实际问题。《 Beginning C, 5th Edition》是一本全面而实用的C语言学习指南，无论是初学者还是有一定基础的开发者，都能从中受益匪浅。"

CHAPTER 1 ■ PROGRAMMING IN C

Comments

Look at the first line of code in the preceding example:

/* Program 1.3 Another Simple C Program - Displaying a Quotation */

This isn’t actually part of the program code, in that it isn’t telling the computer to do anything. It’s simply a

comment, and it’s there to remind you, or someone else reading your code, what the program does. Anything between

/* and */ is treated as a comment. As soon as your compiler finds /* in your source file, it will simply ignore anything

that follows (even if the text looks like program code) until it finds a matching */ that marks the end of the comment.

This may be on the same line or it can be several lines further on. If you forget to include the matching */, everything

following /* will be ignored. Here’s how you could use a single comment to identify the author of the code and to

assert your copyright:

* Written by Ivor Horton

You can also embellish comments to make them stand out:

/*******************************************

* This is a very important comment *

* so please read this. *

*******************************************/

You can add a comment at the end of a line of code using a different notation, like this:

printf("Beware the Ides of March!"); // This line displays a quotation

Everything following two forward slashes on a line is ignored by the compiler. This form of comment is less

cluttered than the previous notation, especially when the comment is on a single line.

You should try to get into the habit of documenting your programs, using comments as you go along. Your

programs will, of course, work without comments, but when you write longer programs, you may not remember

what they do or how they work. Put in enough comments to ensure that a month from now you (and any other

programmer) can understand the aim of the program and how it works.

Let’s add some more comments to the program:

/* Program 1.3 Another Simple C Program - Displaying a Quotation */

#include <stdio.h> // This is a preprocessor directive

int main(void) // This identifies the function main()

{ // This marks the beginning of main()

printf("Beware the Ides of March!"); // This line outputs a quotation

return 0; // This returns control to the operating system

} // This marks the end of main()

You can see that using comments can be a very useful way of explaining what’s going on in the program. You can

place comments wherever you want in your program, and you can use them to explain the general objectives of the

code as well as the specifics of how the code works.

CHAPTER 1 ■ PROGRAMMING IN C

Preprocessing Directives

Look at the following line of code:

#include <stdio.h> // This is a preprocessor directive

This is not strictly part of the executable program, but it is essential in this case—in fact, the program won’t work

without it. The symbol # indicates this is a preprocessing directive, which is an instruction to your compiler to do

something before compiling the source code. The compiler handles these directives during an initial preprocessing

phase before the compilation process starts. There are quite a few preprocessing directives, and there are usually

some at the beginning of the program source file, but they can be anywhere.

In this case, the compiler is instructed to “include” in your program the contents of the file with the name

stdio.h. This file is called a header file, because it’s usually included at the head of a program source file. In this case

the header file defines information about some of the functions that are provided by the standard C library but, in

general, header files specify information that the compiler uses to integrate any predefined functions or other global

objects within a program. You’ll be creating your own header files for use with your programs. In this case, because

you’re using the printf() function from the standard library, you have to include the stdio.h header file. This is

because stdio.h contains the information that the compiler needs to understand what printf() means, as well as

other functions that deal with input and output. As such, its name, stdio, is short for standard input/output.

All header files in C have file names with the extension .h. You’ll use other standard header files later in the book.

Note ■ Header file names are case sensitive on some systems, so you should always write them in lowercase

in #include directives.

Every C compiler that conforms to the C11 standard will have a set of standard header files supplied with it.

These header files primarily contain declarations relating to standard library functions and macros that are available

with C. Although all C compilers that conform with the standard will support the same basic set of capabilities and

will have the same set of mandatory standard header files available, there are standard header files that are optional,

and in some cases extra library functions can be provided with a particular compiler that may not be available with

other compilers that will typically provide functionality specific to the type of computer on which the compiler runs.

Note ■ All the standard header files are listed in Appendix E.

Defining the main() Function

The next five statements define the function main():

int main(void) // This identifies the function main()

{ // This marks the beginning of main()

printf("Beware the Ides of March!"); // This line outputs a quotation

return 0; // This returns control to the operating system

} // This marks the end of main()

A function is just a named block of code between braces that carries out some specific set of operations. Every C

program consists of one or more functions, and every C program must contain a function called main()—the reason

being that a program always starts execution from the beginning of this function. So imagine that you’ve created,

CHAPTER 1 ■ PROGRAMMING IN C

compiled, and linked a file called progname.exe. When you execute this program, the operating system executes the

function main() for the program.

The first line of the definition for the function main() is as follows:

int main(void) // This identifies the function main()

This defines the start of main(). Notice that there is no semicolon at the end of the line. The first line identifying

this as the function main() has the word int at the beginning. What appears here defines the type of value to be

returned by the function, and the word int signifies that main() returns an integer value. The integer value that is

returned when the execution of main() ends represents a code that is returned to the operating system that indicates

the program state. You end execution of main() and specify the value to be returned in this statement:

return 0; // This returns control to the operating system

This is a return statement that ends execution of main() and returns the value 0 to the operating system. You

return a zero value from main() to indicate that the program terminated normally; a nonzero value would indicate an

abnormal return, which means things did not proceed as they should have when the program ended.

The parentheses that immediately follow the name of the function main enclose a definition of what information

is to be transferred to main() when it starts executing. In this example, there’s the word void between the parentheses,

and this signifies that no data can be transferred to main(). Later, you’ll see how data are transferred to main() and to

other functions in a program.

The main() function can call other functions, which in turn may call further functions, and so on. For every

function that’s called, you have the opportunity to pass some information to it within the parentheses that follow its

name. A function will stop execution when a return statement in the body of the function is reached, and control will

then transfer to the calling function (or the operating system in the case of the function main()). In general, you define

a function so that either it does return a value or it does not. When a function does return a value, the value is always

of a specific type. In the case of main(), the value that is returned is of type int, which is an integer.

Keywords

In C, a keyword is a word with special significance, so you must not use keywords for any other purpose in your

program. For this reason, keywords are also referred to as reserved words. In the preceding example, int is a keyword

and void and return are also keywords. C has several keywords, and you’ll become familiar with more of them as you

learn more of the language. You’ll find a complete list of C keywords in Appendix C.

The Body of a Function

The general structure of the function main() is illustrated in Figure 1-2.

CHAPTER 1 ■ PROGRAMMING IN C

Note ■ You can see that I’ve aligned the braces one below the other in Program 1.3 and indented the statements

between them. I’ve done this to make it clear where the block of statements that the braces enclose starts and finishes.

Statements between braces are usually indented by a fixed amount—usually two or more spaces—so that the braces

stand out. This is good programming style, because it allows the statements within a block to be readily identified.

There are other styles for arranging braces in code. For example:

int main(void) {

printf("Beware the Ides of March!"); // This line outputs a quotation

return 0;

}

Tip ■ With whatever style you use to arrange your source code, the most important thing is to apply it consistently.

Outputting Information

The body of the main() function in the example includes a statement that calls the printf() function:

printf("Beware the Ides of March!"); // This line outputs a quotation

As I’ve said, printf() is a standard library function, and it outputs information to the command line (actually the

standard output stream, which is the command line by default) based on what appears between the parentheses that

immediately follow the function name. In this case, the call to the function displays the simple piece of Shakespearean

advice that appears between the double quotes; a string of characters between double quotes like this is called a string

literal. Notice that this line does end with a semicolon.

Function Arguments

Items enclosed between the parentheses following a function name, as with the printf() function in the previous

statement, are called arguments, and they specify data that are to be passed to the function. When there is more than

one argument to a function, they must be separated by commas.

In the previous example the argument to the function is the text string between double quotes. If you don’t like

the quotation that is specified here, you could display something else by simply including your own choice of words

enclosed within double quotes inside the parentheses. For instance, you might prefer a line from Macbeth:

printf("Out, damned Spot! Out I say!");

Try using this in the example. When you’ve modified the source code, you need to compile and link the program

again before executing it.

Note ■ As with all executable statements in C (as opposed to defining or directive statements) the printf() line must

have a semicolon at the end. A very common error when you first start programming in C is to forget the semicolon.

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