C++编程入门指南：自教宝典

A.Self-Teaching.Guide

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"C++ Demystified: A Self-Teaching Guide" 是由 Jeff Kent 所著的一本实用教程，专为那些希望深入理解 C++ 编程语言的自学者设计。该书以循序渐进的方式引导读者逐步掌握 C++ 的各个方面，从基础知识到高级特性，帮助读者建立起计算机程序和编程语言工作原理的基础。书中内容包括： 1. **介绍**：对 C++ 编程语言的基本概念进行概述，为后续章节打下基础。 2. **如何编写 C++ 程序**：解释程序结构和执行流程，让读者了解 C++ 应用的基本逻辑。 3. **内存与数据类型**：介绍 C++ 中的不同数据类型，如整型、浮点型和字符型，以及它们在内存中的存储方式。 4. **变量**：详细讲解变量的作用、声明和初始化，以及它们在程序中的动态变化。 5. **算术运算符**：教授基本的数学运算符以及如何在代码中应用它们。 6. **决策结构**：探讨 if 和 switch 语句，展示条件控制的使用方法。 7. **嵌套 if 语句和逻辑运算符**：深入理解复杂条件判断的实现。 8. **循环**：讲解 for、while 和 do-while 循环，演示循环结构在程序中的应用。 9. **函数**：介绍函数的定义、调用和作用，提升代码的可重用性。 10. **数组**：讲解数组的概念，以及如何创建和操作数组。 11. **指针**：剖析内存地址和指针的概念，以及它们在数据传递和动态内存管理中的角色。 12. **字符、C 字符串和 C++ 字符串类**：对比不同字符串类型，展示如何处理文本数据。 13. **持久数据：文件输入和输出**：介绍文件操作，包括读写文件的基本步骤和常见库函数。 14. **未来的道路：结构体和类**：预览面向对象编程的核心概念，为高级主题做准备。最后，本书还包含 **期末考试** 和练习题答案，以及 **索引**、**图表目录** 和 **表格目录**，便于读者查找所需信息。如果你正在寻找一条简洁且系统的 C++ 学习路径，这本书将是你的好帮手，它能帮助你从零开始掌握 C++ 编程语言。

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What Is a Programming Language?

When you enter a darkened room and want to see what is inside, you turn on a light

switch. When you leave the room, you turn the light switch off.

The first computers were not too different than that light switch. These early computers

consisted of wires and switches in which the electrical current followed a path dependent

on which switches were in the on (one) or off (zero) position. Indeed, I built such a simple

computer when I was a kid (which according to my own children was back when

dinosaurs still ruled the earth).

Each switch’s position could be expressed as a number: 1 for the on position, 0 for the off

position. Thus, the instructions given to these first computers, in the form of the switches’

positions, essentially were a series of ones and zeroes.

Today’s computers, of course, are far more powerful and sophisticated than these early

computers. However, the language that computers understand, called machine language,

remains the same, essentially ones and zeroes.

While computers think in ones and zeroes, the humans who write computer programs

usually don’t. Additionally, a complex program may consist of thousands or even millions

of step-by-step machine language instructions, which would require an inordinately long

amount of time to write. This is an important consideration since, due to competitive

market forces, the amount of time within which a program has to be written is becoming

increasingly less and less.

Fortunately, we do not have to write instructions to computers in machine language.

Instead, we can write instructions in a programming language. Programming languages

are far more understandable to programmers than machine language because

programming languages resemble the structure and syntax of human language, not ones

and zeroes. Additionally, code can be written much faster with programming languages

than machine language because programming languages automate instructions; one

programming language instruction can cover many machine language instructions.

C++ is but one of many programming languages. Other popular programming languages

include Java, C#, and Visual Basic. There are many others. Indeed, new languages are

being created all the time. However, all programming languages have essentially the

same purpose, which is to enable a human programmer to give instructions to a computer.

Why learn C++ instead of another programming language? First, it is very widely used,

both in industry and in education. Second, many other programming languages, including

Java and C#, are based on C++. Indeed, the Java programming language was written

using C++. Therefore, knowing C++ makes learning other programming languages easier.

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Anatomy of a C++ Program

It seems to be a tradition in C++ programming books for the first code example to output

to a console window the message “Hello World!” (shown in Figure 1-1).

Figure 1-1: C++ program outputting “Hello World!” to the screen

Note

The term “console” goes back to the days before Windows when the screen did

not have menus and toolbars but just text. If you have typed commands using

DOS or UNIX, you likely did so in a console window. The text “Press any key to

continue” immediately following “Hello World!” is not part of the program, but

instead is a cue for how to close the console window.

Unfortunately, all too often the “Hello World!” example is followed quickly by many other

program examples without the book or teacher first stopping to explain how the “Hello

World!” program works. The result soon is a confused reader or student who’s ready to

say “Goodbye, Cruel World.”

While the “Hello World!” program looks simple, there actually is a lot going on behind the

scenes of this program. Accordingly, we are going to go through the following code for the

“Hello World!” program line by line, though not in top-to-bottom order.

#include <iostream>

using namespace std;

int main(void)

{

cout << "Hello World!";

return 0;

}

Note

The code a programmer writes is referred to as source code, which is saved in a

file that usually has a .cpp extension, standing for C++.

The main Function

As discussed in the “What Is a Programming Language?” section, the purpose of C++, or

any programming language, is to enable a programmer to write instructions for a

computer. Often, a task is too complex for just one instruction. Instead, several related

instructions are required.

A function is a group of related instructions, also called statements, which together

perform a particular task. The name of the function is how you refer to these related

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Anatomy of a C++ Program

statements. In the “Hello World!” program, main is the name of a function. A program may

have many functions, and in Chapter 9 I will show you how to create and use functions.

However, a program must have one main function, and only one main function. The

reason is that the main function is the starting point for every C++ program. If there was

no main function, the computer would not know where to start the program. If there was

more than one main function, the program would not know whether to start at one or the

other.

Note

The main function is preceded by int and followed by void in parentheses. We

will cover the meaning of both in

Chapter 9.

The Function Body

Each of the related instructions, or statements, which belong to the main function are

contained within the body of that function. A function body starts with a left curly brace, {,

and ends with a right curly brace, }.

Each statement usually ends with a semicolon. The main function has two statements:

cout << "Hello World!";

return 0;

Statements are executed in order, from top to bottom. Don’t worry, the term “executed”

doesn’t mean the statement is put to death. Rather, it means that the statement is carried

out, or executed, by the computer.

cout

The first statement is

cout << "Hello World!";

cout is pronounced “C-out.” The “out” refers to the direction in which cout sends a stream

of data.

A data stream may flow in one of two directions. One direction is input—into your program

from an outside source such as a file or user keyboard input. The other direction is output

—out from your program to an outside source such as a monitor, printer, or file.

cout concerns the output stream. It sends information to the standard output device. The

standard output device usually is your monitor, though it can be something else, such as

a printer or a file on your hard drive.

The << following cout is an operator. You likely have used operators before, such as the

arithmetic operators +, –, *, and /, for addition, subtraction, multiplication, and division,

respectively.

The << operator is known as the stream insertion operator. It inserts the information

immediately to its right—in this example, the text “Hello World!” into the data stream. The

cout object then sends that information to the standard output device—in this case, the

monitor.

Note

In Chapter 3, you will learn about the counterparts to the cout object and the <<

operator, the cin object, which concerns the input stream, and the >> operator

used with the cin object.

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Anatomy of a C++ Program

The return 0 Statement

The second and final statement returns a value of zero to the computer’s operating

system, whether Windows, UNIX, or another. This tells the operating system that the

program ended normally. Sometimes programs do not end normally, but instead crash,

such as if you run out of memory during the running of the program. The operating

system may need to handle this abnormal program termination differently than normal

termination. That is why the program tells the operating system that this time it ended

normally.

The #include Directive

Your C++ program “knows” to start at the main function because the main function is part

of the core of the C++ language. We certainly did not write any code that told the C++

program to start at main.

Similarly, your C++ program seems to know that the cout object, in conjunction with the

stream insertion operator <<, outputs information to the monitor. We did not write any

code to have the cout object and the << operator achieve this result.

However, the cout object is not part of the C++ core language. Rather, it is defined

elsewhere, in a standard library file. C++ has a number of standard library files, each

defining commonly used objects. Outputting information to the monitor certainly is a

common task. While you could go to the trouble of writing your own function that outputs

information to the screen, a standard library file’s implementation of cout saves you the

trouble of “reinventing the wheel.”

While C++ already has implemented the cout object for you in a standard library file, you

still have to tell the program to include that standard library file in your application. You do

so with the #include directive, followed by the name of the library file. If the library file is a

standard library file, as opposed to one you wrote (yes, you can create your own), then

the file name is enclosed in angle brackets, < and >.

The cout object is defined in the standard library file iostream. The “io” in iostream refers

to input and output—“stream” to a stream of data. To use the cout object, we need to

include the iostream standard library file in our application. We do so with the following

include directive:

#include <iostream>

The include directive is called a preprocessor directive. The preprocessor, together with

the compiler and linker, are discussed later in this chapter in the section “Translating the

Code for the Computer.” The preprocessor directive, unlike statements, is not ended by a

semicolon.

Namespace

The final statement to be discussed in the Hello World! example is

using namespace std;

C++ uses namespaces to organize different names used in programs. Every name used

in the iostream standard library file is part of a namespace called std. Consequently, the

cout object is really called std::cout. The using namespace std statement avoids the need

for putting std:: before every reference to cout, so we can just use cout in our code.

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