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InformIT Visual Tutorial 7: Vampire Bots and Code Improvisation in C#, (Part 2 of 2)

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In the conclusion of their two-part tutorial, Nick and Nancy Flor show you how to create a basic vampire bot — a program that drains content from web sites.
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Important Note

The vampire bot discussed in this article writes files to the user's hard drive. If the bot is implemented incorrectly, damage may result and data may be destroyed. Proceed with caution.

Vampire bot is a term we made up for programs that "drain" content out of web sites. We use vampire bots and the C# programming language as a backdrop for teaching you code improvisation—a semi-structured technique for developing code when you program recreationally.

Level: Advanced Beginning Programmer

Assumes that the reader has written at least one C++ or Java program and is comfortable with the syntax for methods and classes. Also assumes that the reader has successfully installed the Microsoft .NET Framework SDK (see InformIT Visual Tutorial 6). You can find the SDK here.

Introduction

Programming is one of the most enjoyable and rewarding of mental activities. As a programmer, you are an information or "computational" artist (see note)—taking reality or imagination and expressing it on an electronic canvas for others to use or enjoy. And like any artistic endeavor—whether painting, music, or even a martial art such as judo—it takes a long while for a practitioner to become proficient. But people keep at it because, as they're learning (and this is very important), they can see or experience results that are both immediate and significant. This is where programming differs from the other arts. A novice programmer experiences more frustration than results, in the form of compilation errors and execution bugs (to name a few). Moreover, in learning to program, the novice is given programming tasks that are probably not very interesting. So it's not surprising that many people don't become proficient at programming—or even bother learning to program.

NOTE

Some programmers take offense at the notion that what they do is art, instead preferring to view it as engineering. But the two terms are not mutually exclusive when you look at programming in terms of product and process. The product of programming can be viewed as a piece of art—an individual or group's unique expression of an idea or specification. The process that programmers use to create the product can be (software) engineering, such as object-oriented analysis and design, or the process can be more freehand—just sitting down and typing code "off the top of your head."

To alleviate these problems, we take a software archetype approach to teaching programming to beginners. Beginners don't learn by just building programs from scratch; instead, we give them useful working programs and have them modify these programs to suit their specific needs. Now, although we give beginners working programs, these programs typically just implement some basic function in the most straightforward manner possible. Beginners have to modify these archetypes by enhancing functionality, adding error handling, and coding more efficient algorithms, just to name a few. In our experience, by modifying these archetypes to suit specific needs, a beginner internalizes the knowledge needed to create them in their entirety.

Finally, all the practice in the world won't amount to much if your technique is inefficient. When programming recreationally and when modifying archetypes, beginners have a tendency to code kludges—poorly-fitting code pieces that are difficult to debug and understand. So, in addition to the software archetype approach to teaching programming, we also teach beginners a semi-structured methodology known as code improvisation for developing new programs and also for understanding existing ones. For people learning how to program and for those programming recreationally, code improvisation keeps design activity to just the bare minimum and implementation at the forefront, which helps keep programming fun. Now, before the software engineering design purists get upset, note that we aren't advocating using code improvisation for industrial software development—just for recreational software of small and medium complexity.

In this article, the software archetype that we'll discuss is a basic vampire bot—a term we developed for a program that drains content from other web sites. As the vampire bot is an archetype, it only downloads GIF files from a single web page. It's your task after completing this tutorial to modify it to download other image types and to crawl across multiple web pages as well as add the error-handling code to make it robust. The key code blocks (motifs) needed to do so are contained within the archetype, if you understand how it works. Before going over the vampire bot's implementation, let's first discuss code improvisation.

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