理解计算机科学家的思考方式：C++版

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"如何像计算机科学家一样思考(C++版)" 是一本由Allen B. Downey编写的书籍，旨在教授编程思维，特别关注C++语言。这本书的原始版本是用LaTeX编写，可以生成设备无关的文本表示，并能转换为其他格式或打印。源代码可以在作者的网站或Google Code的SVN仓库中找到。书中内容涵盖了编程语言的基本概念，包括： 1. **编程语言是什么？** - 编程语言是人与计算机之间交流的一种形式，它允许我们用结构化的方式描述指令，让计算机执行特定任务。 2. **什么是程序？** - 程序是一系列按照特定顺序执行的指令，用于解决特定问题或实现特定功能。它们可以控制硬件、处理数据、提供用户界面等。 3. **什么是调试？** 调试是找出并修复程序错误的过程，它分为几个阶段： - **编译时错误**：在程序编译期间发生的错误，通常是语法错误，如拼写错误、缺少分号或括号不匹配等。编译器会检测并指出这些错误。 - **运行时错误**：程序在执行过程中出现的问题，如除以零、数组越界或无效的操作。这些错误通常会导致程序崩溃或产生意外结果。 - **逻辑错误和语义**：即使程序没有语法错误或运行时错误，也可能因为逻辑错误（即程序员的思维错误）导致程序行为不符合预期。这涉及到程序的语义，即代码实际表达的意义。 - **实验性调试**：通过观察程序运行、使用断点、单步执行、变量跟踪等方式来定位和修复逻辑错误。 4. **形式与自然语言** - 讨论了编程语言与人类自然语言的区别，以及如何将自然语言的思想转化为计算机可理解的形式。该书深入浅出地介绍了编程的基本原理，不仅适合初学者，也对有经验的开发者有启示作用。通过学习，读者将能够培养解决问题的逻辑思维，理解计算机如何处理信息，并掌握有效的调试技巧，从而更高效地编写和维护C++代码。

8 CHAPTER 1. THE WAY OF THE PROGRAM

endl is a special symbol that represents the end of a line. When you send

an endl to cout, i t causes the cursor to move to the next line of the display.

The next time you output something, the new text appears on the next line.

Like all statements, the output statement ends with a semi- colon (;).

There are a few other things you should notice about the sy ntax of this

program. First, C++ uses squ iggly-b r aces ({ and }) to group things together.

In this case, the output statement is enclosed in squiggly-braces, indicating that

it is inside the deﬁnition of main. Also, notice that the statement is indented,

which helps to show visually which lines are inside the deﬁnition.

At this point it would be a good idea to sit down in front of a computer and

compile and run this program. The details of h ow to do that depend on your

programming environment, bu t from now on in this book I wil l assume that you

know how to do it.

As I mentioned, the C++ compiler is a real sti ckler for syntax. If you make

any errors when you type in the program, chances are that it will not compile

successfully. For example, if you misspell iostream, you might get an error

message like the following:

hello.cpp:1: oistream.h: No such file or directory

There is a lot of information on this line, but it is presented in a dense format

that is not easy to interpret. A more friendly compiler might say something

like:

“On line 1 of the source code ﬁle named hello.cpp, you tr ied to

include a header ﬁle named oistream.h. I didn’t ﬁnd anything with

that name, but I did ﬁnd something named iostr eam. Is that what

you meant, by any chance?”

Unfortunately, few compilers are so accomodating. The compiler is not really

very smart, and in most cases the error message you get will be only a hint about

what is wrong. It will take some time to gain facility at interpreting compiler

messages.

Nevertheless, the compiler can be a useful tool for learning the syntax rules

of a language. Starting with a working program (like hello.cpp), modify it

in various ways and see what happens. If you get an error message, try to

remember what the message says and what caused it, so if you see it again in

the future you will know what it means.

1.6 Gloss a ry

problem-solving: The process of formulating a problem, ﬁnding a solution,

and expressing the solution.

high-level language: A programming language like C++ that is designed to

be easy for humans to read and write.

12 CHAPTER 2. VARIABLES AND TYPES

In this case the output appear s on a single line as Goodbye, cruel world!.

Notice that there is a space between the word “Goodbye,” and the second

quotation mark. This space appears in the output, so it aﬀects the be havior of

the program.

Spaces that appear outside of quotation mark s generally do not aﬀect the

behavior of the program. For example, I could have written:

int main ()

{

cout<<"Goodbye, ";

cout<<"cruel world!"<<endl;

return 0;

}

This program would compile and run just as well as the original. The breaks

at the ends of lines (newlines) do not aﬀect the program’s behavior either, so I

could have written:

int main(){cout<<"Goodbye, ";cout<<"cruel world!"<<endl;return 0;}

That would work, too, although you have pr obabl y noticed that the program is

getting harder and harder to read. Newlines and spaces are useful for organizing

your program visually, making it easier to read the program and locate syntax

errors.

2.2 Values

A value is one of the fundamental things—like a letter or a number—that a

program manipulates. The only values we have manipulated so far ar e the string

values we have been outputting, like "Hello, world.". You (and the compiler)

can identify string values because they are enclosed in quotation marks.

There are other kinds of values, including integers and characters. An integer

is a whole number like 1 or 17. You can output integer values the same way you

output strings:

cout << 17 << endl;

A character value is a letter or digit or punct uation mark enclosed in single

quotes, like ’a’ or ’5’. You can output character values the same way:

cout << ’}’ << endl;

This example outputs a single close squiggly-brace on a line by itself.

It is easy to confuse diﬀerent types of values, like "5", ’5’ and 5, b ut if you

pay attention to the punctuation, it should be clear that the ﬁrst is a str ing, the

second is a character and the third is an i nteger. The reason this distinction is

important should become clear soon.

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