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像堆�U�木一样学习电脑编�E�，scratch来自�ȝ��理工

Mon, 24 Oct 2011 06:54:00 GMT

官网地址�Q�http://scratch.mit.edu

Scratch是一�U�计��机�~�程语言�Q�利用它可轻村֜�创徏自己的互动故事，动画�Q�游戏，音乐和艺�? 和在�|�络上分享你的作品�?当学生创建和�׃�n自己的Scratch动画�Ӟ��他们能学习到重要的数学和计算知识�Q�同时也得到创造性的思考，�pȝ��推理�Q�和协同工作的机会�?br />
��Z��么要用Scratch学习�~�程�Q?br />1、Scratch上手非常�Ҏ��Q�适于8岁以上孩子，成�h也可以玩。积木，我想大多��C�h应该有玩�q�吧�Q�没实际玩过臛_��也听说过吧。用Scratch�~�程��像玩积木一��P��非常��单，把像一个个�U�木一��L��脚本命��o�Q�按照一定的逻辑堆积��h��Q�就可以做出自己的动��L��游戏了。有图才有真相，各位看官请先看图�?br />

2、Scratch��单，但能做很多事。你可以到官�|�看看一些优�U�的作品，��q��道Scratch能做些什么呢�?br />3、Scratch虽然不用你去敲代码，但它同其它计��机语言的编�E�思想是完全一��L��Q�和C�Q�C++�Q�Java的编�E�思想没什么两栗��如果你懂C、C++或Java�Q�那些堆�U��v来的脚本�Q�也是可以翻译成C、C++、Java代码的，�q�且非常��单，�l�对要比��p��译��单很多很多�?br />

4、Scratch是免费的�Q�可以在Mac�Q�Windows和Linux上运行，�q�且软�g的语�a�是可以设�|�，不懂英文也不要怕，可以把��Y件界面语�a�讄��为简体中文。官�|�的站点也有中文的版面�?/div>5、网站的用户参与度非帔R��Q�用户可以上传自��q��作品到该�|�站�Q�可以欣赏其他用��L��作品�Q�看到喜�Ƣ的也可以下载下来研�I�研�IӞ��当然也可以用到自��q��作品中哦�?br />
Scratch的一些统计数据，从其中你��可以看出此软�g有多优秀�Q�看�q�之后是否选择此编�E�语�a�做�ؓ自己的入门语�a��Q�那��q��你的了�?br />�W�一�q�图�Q�scratch�|�站的访问者都来自哪些城市

�W�二�q�图�Q�scratch�|�站的注册用户年龄分布图�Q�蓝色代表男性，�U�色代表��x��）

黄剑�?/a> 2011-10-24 14:54 发表评论

��Z��么学习C

Thu, 20 Oct 2011 09:07:00 GMT

原文地址�Q�http://www.cprogramming.com/whyc.html

��Z��么学习C

Why Learn C?

现在大家在用的计��机语言的数量多得可怕。从高��语言�Q�比如VB�Q�到低��语言�Q�有非常多的选择�Q�Perl�Q�Ruby和Python语言�Q�对于很多�Q务的实现都是不错的选择�Q�。Java已经成�ؓ了一些项目非常受�Ƣ迎的语�a��Q�某�U�程度上也是因�ؓ它拥有大量的API和虚拟机机制提供了比较好的安全性。（内存垃圾攉��器也是一个非�怸�错的功能�Q�可以��得程序员更有效率。）
There are an awful lot of programming languages available right now -- everything from the extremely high level (such as Visual Basic) to the low level power of assembly, and a good variety of specialized options in between (Perl, Ruby, and Python are good choices for many tasks). Java has also become quite the hot programming language for some tasks, in part because of its large API and in part because the virtual machine provides some elements of security. (Garbage collection is another nice feature and can make programmers much more efficient.)
然而，学习c语言�~�程�Q�也有很多很好的理由。第一�Q�历史悠久：C语言已有30多年的历史了�Q�译者注�Q�到现在已有�q?0�q�了�Q�，能找到大量的有效的源代码。这也意味着有很多可以学习的例子�Q�也有很多是可以直接拿来用的代码。而且�Q�语�a�的很多问题都已经说明的很清楚--它可以更好的理解�Q��ƈ且你可以扑ֈ�很多很不错的教程。另外，对于C�Q�你可以获得很多你能理解的看法和见解�?/div>

Nevertheless, there are some good reasons to learn to program in C. First, age has its advantages: C has been around for 30 years, and there is a ton of source code available. This means there's a lot to learn from, and a lot to use. Moreover, many of the issues with the language have been clearly elucidated -- it's well understood, and you can find a lot of tutorials available. Plus, with C, you get lots of strong opinions mixed with insights that you can understand.

�׃��历史的原因，C做�ؓUnix的一个系�l�编�E�语�a��Q�C已经成�ؓ了一门通用的编�E�语�a�。有时候用C语言来表达一些编�E�上的想法，大部分�h都会感觉到比较舒服�?br /> As a result of its age and its use as the language of system programming for Unix, C has become something of the lingua franca of programming. C is a great language for expressing common ideas in programming in a way that most people are comfortable with. Moreover, a lot of the principles used in C -- for instance, argc and argv for command line parameters, as well as loop constructs and variable types -- will show up in a lot of other languages you learn so you'll be able to talk to people even if they don't know C in a way that's common to both of you.

�W�三�Q�C是比较接�q�机器语�a��?br /> Third, C is reasonably close to the machine. When you're working with pointers, bytes, and individual bits, things like optimization techniques start to make a lot more sense. There's also utility in knowing exactly how something works underneath the hood -- this helps a great deal when something you're trying to do in a higher level language seems way slower than expected, or just doesn't work at all. You also tend to get a better picture of advanced topics like exactly how networking works. A higher level language will make it a little bit simpler, but it'll be harder to understand what's going on, and when things stop working, it's much better to know exactly what's going on so you can fix it. Additionally, if you like computer science as a discipline, or just like knowing how things work learning the details of the system is great fun.

实际上，很多有趣的编�E�都可以用C来做--比如�Q�系�l��Y件和数据��理�pȝ��Q�Berkeley DB�Q�。如果你惛_��一个比较复杂的web�E�序�Q�C也是一个很不错的选择。如果你惛_��一个非常好的，快的�Q�C也是很好的选择。你可以用C来写整个操作�pȝ��Q�想用Java来做�q�个事情是非帔R��的，对于脚本语言来说是几乎不可能的。而且C是一门非常简�z�精炼的语言�Q�它使得非常有趣的编�E�看��h��更优雅，你的�~�程之旅��会有一个很好的开始�?br /> In fact, a lot of fun programming is done in C -- for instance, system software and data managers such as Berkeley DB. If you want to be able to do more than write a simple web app, C is a great language. If you want to write a great, fast game, C is again a great choice. You can write an entire OS in C. It'll be much harder to do so in Java, and nearly impossible in a scripting language. And the language, being succinct as C is, will probably make your fun program more elegant looking to boot.

我对于这��文章所谈的话题�Q�想补充几点�?br />

1、学好C�Q�可以帮助理解其他语�a�中的一些概��c�?br />比如Java中的引用的概念，如果理解了C语言中的指针的概念，��p��很好的理�?#8220;引用”�q�个概念了，而不理解指针的概忉|��把引用的概念理解的很透彻�Q�是比较隄��?/div>
2、学会了C语言�Q�再学习其他语言会感觉到更轻松�?br />

Object-C�Q�Java�Q�C++�{�等很多高��语言的语法都与C是相似的。学会了C后，基本上只要花上一周的旉��了解一下其他语�a�的特性，��基本上可以看懂其他语言的源代码了�?/div>
3、从现实角度来考虑�Q�学好C�Q�找��C��份好工作的可能性也是大大增强，特别是对于刚毕业的大学生�Q�或工作�l�验比较��的�E�序员。现在需要有C语言基础�Q�擅长于C语言的，工作岗位也是比较多。比如拿现在非常��行的iPhone�Q�iPad�{�设备的应用�E�序�Q�开发语�a��是Objective-C语言。Objective-C是苹果Mac OS X、iOS�q�_��的开发语�a��Q�Objective-C是基于C语言的，增加面向对象的相关特性。你可以认�ؓObjective-C��是另一个版本的C++�Q�也��是采用了与C++不同的语法，但也实现了面向对象。你有了C语言的基��Q�再学Objective�Q�难度就不大了�?br />你可以到那些招聘�|�站�ȝ��看，查查iPhone相关的开发工�E�师的要求，是不是很多都要求有C/C++的基��和经验�?br />�q�有一些系�l�开发和底层比较相关的，很多都是需要用C语言开发的。拿信息安全行业来讲�Q�很多安全��品都是用C语言来开发的。还有游戏行业很多都是用C或C++�?br />
�q�有一点，很多初学者认为学习C很难。其实我惌��的是隑�ƈ不是计算��a�的问题，隄��是因��Z��用计��机解问题的思维�q�没建立��h��。因��Z��q�入的是一个新的领域，以前没有接触�q�计��机�~�程�Q�对于怎么用计��机来解决现实中的问题的�q�种思维你还没有建立��h��Q�毕竟用计算��题的思维�Q�和用数学解题的思维�q�是有些不一��L��Q�所以你会觉得学习C语言很难�?br />如果你在学习C语言的同�Ӟ��再进行一些程序员的思维训练�Q�我觉得情况��׃��大有改善�?/div>

黄剑�?/a> 2011-10-20 17:07 发表评论

初学者指南：How To Think Like A Programmer

Wed, 19 Oct 2011 15:03:00 GMT

Over the past decade-and-a-half of teaching introductory computer programming I have noticed increasingly that students have difficulty with solving problems. It is common to see learners read a programming problem description and immediately try to write the programming language source code (usually whilst sitting at a PC typing straight into the editing window of the compiler environment). When they ask for help it is often the case that their difficulty lies not with manipulating the programming language syntax (C, Pascal, Java, or whatever) but in understanding what it is they're trying to solve. In fact, many times they confuse their syntax-handling difficulties with their problem-solving difficulties and blame their frustration on programming itself or on the chosen programming language. Some of them then become so downhearted that they decide they cannot do computer programming and transfer to a course that doesn't require them to study it.

�q�个话题挺有意思，我看了他的练习题�Q�还真不错，有时候觉得。算法和计算机的语言的学习应该是有另外一�U�方式�?br />换句话说�Q�在深入学习语言和算法，可以先来一��开胃菜�?br />�|�站地址�Q?div>http://www.howtothinklikeaprogrammer.com/forum/index.php

书名�?《How to Think Like a Programmer: Program Design Solutions for the Bewildered》By Paul Vickers�?/div>

黄剑�?/a> 2011-10-19 23:03 发表评论

Wed, 19 Oct 2011 03:00:00 GMT

原文�Q�http://www.cprogramming.com/tutorial/thinking.html

很多人通过Email问我�Q�怎样开始写一个程序。也许最好的��非常��单，把程序的步骤写下来：一旦你开始把��x��或者代码写下来后，你就会对你的��目有一些感觉了。通常�E�序设计有两�U�通用的做法：从上��C��的方式和从下��C��的方式�?br /> A lot of people email me asking the way to start some program or another. Perhaps the best advice is simply to start writing down a layout for the program: once you start writing down ideas or code you'll start to get a feel for your project. There are two standard methods of program design: the top-down approach and the bottom-up approach. Top-down programming involves writing code that calls functions you haven't defined and working through the general algorithm before writing the functions that do the processing. Top-down programming is, to a good degree, a very abstract way of writing code because it starts out by using functions you haven't designed, and that you perhaps do not know how to design. The bottom-up approach to programming is the opposite: the programmer writes the basic functions she realizes will be necessary at some point in the programming and then work up to the more complex parts of the program.

比较有意思的是，那两�U�方法都是关注程序中要执行的动作或方法，而不是关注程序要处理的数据。很多时候，写程序最好的�Ҏ��是，写出你将要用到或处理的数据，然后再从上到下的��x��么样去处理�q�些数据�Q�最后才能得��C��需要的�l�果。首先定义数据，然后再写出那些要处理�q�些数据的相关的函数。，�q�样你才会得��C��的程序应该怎样写的基本思�\�Q?br />

It's interesting that both of these approaches focus on the actions of the program rather than the objects the program manipulates - variables. Many times, the best way to write a program is to figure out the variables you need to work with and then progress with a top-down approach to the program that manipulates those variables. By defining variables first and then working with functions that work on them, you will always maintain a basic foundation of what your program should be doing. Once you have an idea of what variables you will be using, then you can write functions to perform the operations you need to perform on the variables while maintaining sight of the goal. Finally you can write the code for each individual function.

Another value to defining variables before writing code is that many times you can accomplish an entire program without many functions; this fact is especially true when you are a beginner making simple programs. The variables give you the raw materials you need to begin working with the tools: loops, if statements, library functions, and perhaps user defined functions.

现在让我们来看一个关于怎样开始写一个完整程序的例子。假设你要写的程序是要模拟一个DVD商店的租售系�l�，�q�个�pȝ��需要计��出出租DVD的��L��入。你的程序有可能要求�Q�需要输入一个代码，告诉你这个DVD�U�售的�h格是2元一天还是是3元一天，然后�q�需要它出租了多��天�Q�最后如果这个输入的代码�?�Q�整个程序就�l�束了。你应该要分别计��出�U�金�?�?天和2�?天的DVD的出�U�的��d��数。拿�q�个�E�序来说�Q�思考设计程序的最好的方式是，惌��Z��计算出租金的收入�Q�你需要存储哪些信息：

你需要一个变量用来存储��L��入，当程序结束时;
你需要一个��时变量用来存储代表DVD的租金的代号;
你需要一个��时变量用来存储某个DVD出租的天�?
你需要一个变量来存储�U�金�?�?天的所有DVD出租了多��天的��L��;
最后，你还需要一个变量来存储�U�金�?�?天的所有DVD出租了多��天的��L��;

Let's take a look at an example of how to go about thinking about a program. If you were to write a program to simulate a video store rental system that calculates the gross revenue from rentals, you might be asked to write a program that accepts a code telling you whether a certain video was rented at $2.00 (input as 2) a day or $3.00 (input as 3) a day and then asks for how many days it was rented out for; finally, if the code for the cost of rental is 0 the program should terminate. You should also count the number of days videos were rented at $3.00 per day and $2.00 per day. The best way to think about the design for a program such as this one is to imagine what information you need to store in order to calculate the revenue:

you need a variable to store the total dollar amount at the end of the program;
you need a temporary variable to store the code for the cost of a transaction;
you need a temporary variable to store the number of days a specific video was rented;
you need a variable to store the number of days each video was rented;
you need a variable to count the total number of days $3.00 videos were rented;
finally, you need a variable to count the total number of days $2.00 videos were rented.

一旦你认识��C��需要这些数据，那么你就很容易想出如何处理这些数�?比如�Q�你知道�U�金2�?天的DVD的��L��?所有租金�ؓ2�?天DVD的出�U�天��C��?2�Q�类似的也可以计��出�U�金3�?天的DVD的��L��入。你也会理解�q�个“代表DVD的租金的代号”�Q�这个变量的用处是，当用戯��入某个DVD出租的天数时�Q�决定哪个变量会被操作。在你的�E�序中你需要一个��@环结构�?/p>

Once you realize you need these variables, you can easily imagine how to translate them in terms of each other: for example, you know the total amount of revenue is the number of days videos at $2.00 were rented times $2.00; in similar fashion, you know the relationship for $3.00 a day videos. You should understand that the transaction 'code' determines which variables are manipulated when the user inputs the number of days a specific video was rented (for example, whether to add to the count of days for $2.00 videos or $3.00 videos). You'll probably need a loop in your program (although you can't necessarily infer this from the variables).

�E�序的代码有可能会像下面那样�Q?br />

The code might look as follows:

1
3 int main()
4 {
5   int total_dollars = 0;
6   int total_days_at_3_dollars = 0;
7   int total_days_at_2_dollars = 0;
8   int transaction_code = 0;
9   int days_for_one_video = 0;
10   do
11   {
12     if(transaction_code==2)
13       total_days_at_2_dollars+=days_for_one_video;
14     if(transaction_code==3)
15       total_days_at_3_dollars+=days_for_one_video;
16     cout<<"Please enter a transaction code and number of days a video was rented: ";
17     cin>>transaction_code>>days_for_one_video;
18   }while(transaction_code!=0)
19   return 0�Q?br /> 20 }

我希望，你现在已�l�有了一个基本的思�\�Q�在写代码之前，应该如何安排你的�E�序的结构�?br />

Hopefully, you now have a basic idea of how to lay out your program structure in your mind before you begin to write code.

黄剑�?/a> 2011-10-19 11:00 发表评论