ASP.NET PDF Viewer using C#, VB/NET

When you type letters in the New Article Title text box, autocomplete will kick in and render similar articles in the space beneath. See Figure 7-21 for an example that works if you enter the letters CRE.

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The image data is calculated by converting the red, green, and blue values of each pixel to an average gray scale value The value is then shifted down and masked to three bits, giving the value range 0 7 This value corresponds to the darkness of each pixel and is used to look up a character in the map string The map variable is a char* initialized to :ilNAM (including an initial space) The characters in the map string have been picked so that the lowest value is white, and each character gets darker and darker as the index increases The source image and the resulting ASCII art can be seen in Figure 11-3 The ASCII art is shown in a word processor using a monospace font set to a very small size.

Notice that the namespace is followed by an open brace ({). C# uses braces to denote containment here, everything inside these braces will be in our HelloWorld namespace. Since namespaces contain types, it should come as no great surprise that the next line in the file defines a type. Specifically, it defines a class. The .NET Framework class library isn t the only thing that gets to define classes in fact, if you want to write any code at all in C# you must provide a type to contain that code. Some languages (such as C++) do not impose this constraint, but C# is an objectoriented (OO) programming language. We ll explore OO concepts in the next chapter, but the main impact on our Hello, world example is that every bit of C# code must have a type that it calls home. There are a few different ways to define types in C#, which we ll get to in the next few chapters, but for the present simple example, the distinctions are not yet relevant. So we use the most common, a class:

class Program { ... }

Again, note the braces as with the namespace contents, the class s contents are delineated by a pair of braces. We re still not quite at the code yet code lives inside a class, but more specifically, it must live inside a particular method inside a class. A method is a named block of code, which may optionally return some data. The class in our example defines a method called Main, and once again we use a pair of braces to show where it starts and ends:

static void Main(string[] args) { ... }

When all image data is written to the stream, the stream s good status is ensured before true is returned for a successful write operation Listing 11-7 Writing the image to a device bool TextImageHandler::write( const QImage &image ) { QTextStream stream( device() ); stream << "TEXT\n"; stream << imagewidth() << "x" << imageheight() << "\n"; for( int y=0; y<imageheight(); ++y ) { for( int x=0; x<imagewidth(); ++x ) { QRgb rgb = imagepixel( x, y ); int r = rgb & 0xff; int g = (rgb >> 8) & 0xff; int b = (rgb >> 16) & 0xff; stream << map[ 7 - (((r+g+b)/3)>>5) & 0x7 ]; } stream << "\n"; } if( stream.

The first keyword here, static, tells C# that it s not necessary to create a Program object (Program being the class that contains this method, remember) in order to use this method. As you ll see in the next chapter, a lot of methods require an object, but our simple example doesn t need one.

The next keyword is void This tells the compiler that our method doesn t return any data it just does some work Many methods return information For example, the SystemMath class s Cos method calculates the cosine of its input, and since it doesn t know what you want to do with that result, it provides it as a return value the output of the method But the code in this example is rather more proactive than that it decides to show a message on the screen, so there s nothing for it to return On methods that return data, you d write the type of data being returned here, but since there s nothing to return in this case, the nothingness is denoted by the void keyword The next part, Main, is the name of the method.