C语言与GUI编程入门

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"《An Introduction to C & GUI Programming (2019)》是一本针对初学者介绍C语言编程及GUI编程的书籍。作者通过这本书引导读者从零开始学习C语言，并逐步掌握如何使用C语言在Raspbian系统上创建基于GTK工具包的桌面应用程序。读者无需任何编程经验，只需一台运行Raspbian的树莓派即可开始学习。" 本书分为两大部分，首先介绍了C语言编程的基础知识，这对于完全没有编程背景的人来说是至关重要的。C语言是一种强大的、通用的编程语言，它诞生于20世纪70年代，至今仍广泛应用于各种场景，包括创建简单的命令行程序和嵌入式系统。学习C语言的基本结构、语法和控制流是理解编程逻辑和进阶技术的基础。第二部分侧重于图形用户界面（GUI）编程，特别是使用GTK工具包。GTK是一种跨平台的GUI库，支持多种操作系统，包括Raspbian所基于的Linux。通过GTK，开发者可以构建具有丰富视觉效果和交互功能的桌面应用。书中将详细讲解如何使用C语言与GTK结合，创建窗口、控件、布局以及处理用户事件等。在学习C语言时，读者将接触到变量、数据类型、函数、循环、条件语句等核心概念。同时，也会了解到内存管理和指针的重要性，这些都是C语言强大但有时也具挑战性的特性。对于GUI编程部分，读者将学习到如何初始化GTK环境，创建窗口，添加按钮、文本框等元素，以及如何响应用户的点击和输入事件。此外，可能还会涉及信号和回调函数的概念，这是GUI编程中的关键机制。通过这本书，读者不仅可以掌握C语言的基本技能，还能深入理解如何利用这些技能开发用户友好的图形界面。作者Simon Long的指导旨在使学习过程既有趣又实用，让初学者能够快速上手并实际操作。同时，由于Raspbian是基于Debian的轻量级操作系统，特别适合在树莓派这样的小型硬件上运行，因此这本书的内容对于那些对物联网和嵌入式系统感兴趣的读者来说尤为有价值。《An Introduction to C & GUI Programming》不仅是一本C语言的入门教材，更是一本实践导向的GUI编程指南，为有志于探索编程世界的新手提供了全面且实用的知识框架。书中的实例和练习将帮助读者建立起坚实的编程基础，为进一步的学习和发展奠定坚实的基础。

AN INTRODUCTION TO C AND GUI PROGRAMMING16

…you have:

float a;

This tells the compiler that a is now a oating-point value, rather than an integer. Compile

and run your program. What happens?

Oops! That doesn’t look right, does it? What has happened is that, while the maths is still

all correct, the printf statement is now wrong; you’re telling it to print a, which is a oating-

point value, as a decimal integer. To x that, change the rst %d in the printf function to %f,

which is the format specier for a oating-point number, like this:

printf ("The sum of adding %f and %d is %d\n", a, b, c);

That should produce something a lot more sensible when you run it. This is an important

lesson about C: it will do exactly what you tell it to, even if it makes no sense. You told it to

show you a oating-point number as if it were a decimal integer, and the compiler assumed

that was what you wanted, even though the result was nonsense.

When you’re working with variables, always keep track of what values you’re putting in what

types, as it’s easy to introduce errors by assuming a variable is of one type when it’s actually

another. One common error is to put the results of a calculation on oating-point values into

an integer.

Try this: make

b a oat as well (not forgetting to change its format specier in the printf),

but leave c as an int, and set the two oats to values with decimal points, like this:

float a;

float b = 3.641;

int c;

a = 2.897;

c = a + b;

printf ("The sum of adding %f and %f is %d\n", a, b, c);

You’ll see a result like:

The sum of adding 2.897000 and 3.641000 is 6

6? That’s not right! But it’s exactly what you’ve asked for. What the compiler did was to add

the two oating-point values together, and got the answer 6.538, but you then told the compiler

to put that into c, an integer variable. So the compiler just threw away everything after the

decimal point! If you change

c to a oat, and change the nal %d to %f, you’ll nd it gives the

correct answer.

AN INTRODUCTION TO C AND GUI PROGRAMMING20

another set of curly brackets; these contain the operations you want to execute if the original

test evaluated as false.

Try compiling the code above, and change the value with which

a is initialised to make sure

it does what you expect.

= or ==

That’s all ne, but what’s this a == 0 all about? Surely if we want to know whether a is equal

to 0, we just put a = 0? Why the two equals signs? Well, try replacing the double equals sign

with a single equals and see what happens.

This is a very important aspect of C syntax, and a common source of bugs. The equals sign

is used for two different things: one is to assign a value to a variable, whereas the other is to

test whether a variable is equal to a value. A single equals sign (=) assigns a variable; a double

equals sign (==) tests a variable.

So the statement…

if (a == 0)

…tests to see if a is equal to 0. If it is, then the test evaluates as true, and the code

immediately after the if is executed.

But the statement…

if (a = 0)

…doesn’t compare a against 0 at all: it just sets a to 0. So how does the compiler decide

what to do next? In this case, it just looks at the value of what’s in the brackets; you’ve set a to

0, so the value inside the brackets is 0.

In C, a value of 0 is equivalent to false, and a non-zero value is equivalent to true. So by

replacing the double equals with a single equals, you’ve changed the value of a, and then you

look to see if the value you’ve set a to is equivalent to true or false; neither of which were what

you wanted to do! If a C program is behaving strangely, check very carefully that all your tests

are actually tests and not assignments: this is a very easy mistake to make.

So == is the test to see if a value is equal to another one. There are other useful

symbols that can be used in a test. The symbol !=, for example, means ‘is not equal to’.

CURLY BRACKETS

Curly brackets are used to group together a set of statements which always execute together.

If your loop or if statement only needs to execute one single statement, you can leave out the

curly brackets after the test, but this can make the code's purpose less obvious to ahuman!

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C语言与GUI编程入门

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