Simple .NET/ASP.NET PDF document editor web control SDK

The int type (short for integer) represents whole numbers. That s clearly no use for our example, because we re dealing with numbers such as 5.14, and the closest that an int can get to that value is 5. But programs often deal with discrete quantities, such as the number of rows returned by a database query or the number of employees reporting to a particular manager. The principal advantage of an integer type is that it s exact: there s no scope for wondering if the number is really 5, or maybe just a number quite close to 5, such as 5.000001. Table 2-1 lists nine types capable of representing integers. The ninth, BigInteger, is a special case that we ll get to later. The other eight support four different sizes, with a choice between the ability and inability to represent negative numbers. Unsigned numbers may seem less flexible, but they are potentially useful if you need to represent values that should never be negative. However, the unsigned integer types are not widely used some programming languages don t support them at all, and so you ll find that the .NET Framework class library tends to use the signed types even

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Note The properties that can be used when connecting to a database are hostName, databaseName,

Several types of server controls exist: HTML server controls: These classes wrap standard HTML tags but are declared with the runat= server attribute An example is the HtmlAnchor control, which is a server-side representation of the <a>, or anchor, tag Web controls: These classes duplicate the functionality of basic HTML tags but have methods and properties that have been standardized across their entire range, making it easier for developers to use them Many of them are analogous to HTML server controls (for example, the button), but their APIs have been designed to be used by C# and other NET developers, as opposed to being an echo of the API used by the standard HTML controls As such, they are more consistent to use when developing applications, particularly if you don t have much experience hand-coding HTML.

when the unsigned ones might make more sense. For example, the Count property available on most collection types is of type int a signed 32-bit integer even though it does not make sense for a collection to contain a negative number of items.

Unsigned integers can also represent larger numbers than their signed equivalents. They don t need to use up a bit to represent the sign, so they can use that to extend the range instead. However, this is something you should be wary of depending on. If you re so close to the limits of a type s range that one more bit makes a difference, you re probably in danger of overflowing the type s range in any case, and so you should consider a larger type.

Besides the signed/unsigned distinction, the various types offer different sizes, and a correspondingly different range of values. 32 bits is a popular choice because it offers a usefully wide range of values and is efficient for a 32-bit processor to work with. 64bit types are used for the (fairly rare) occasions when you re dealing with large enough quantities that a 32-bit representation s range of a couple of billion is insufficient. 16bit values are rarely used, although they occasionally crop up when having to deal with old programming interfaces, file formats, or network protocols. The 8-bit byte type is important because binary I/O (e.g., working with files or network connections) is mostly byte-oriented. And for reasons of historical convention, bytes buck the trend in that the unsigned type is used more widely than the signed sbyte type. But outside of I/O, a byte is usually too small to be useful. So in practice, int is the most widely used integer type. The fact that C# even offers you all these other choices can seem a little archaic it harks back to the time when computers had so little memory that 32-bit numbers looked like an expensive choice. It gets this from its C-family connections, but it does turn out to be useful to have this control when you need to work directly with Windows APIs, as you ll see in 19. Notice that most of the types in Table 2-1 have two names. C# uses names such as int and long, but the .NET Framework calls these types by longer names such as System.Int32 and System.Int64. The shorter C# names are aliases, and C# is happy to let you use either. You can write this:

Listing 13-1. Connecting to a MySQL server QSqlDatabase db = QSqlDatabase::addDatabase( "QMYSQL" ); db.setHostName( "localhost" ); db.setDatabaseName( "qtbook" ); db.setUserName( "user" ); db.setPassword( "password" ); if( !db.open() ) { qDebug() << db.lastError(); qFatal( "Failed to connect." ); } Listing 13-2 shows how a connection is made to an SQLite database using the QSQLITE driver. The SQLite database is different from the MySQL database because it is not based around a server, so you don t need to log in to the database using a username and password. Instead, you only specify a file name through the databaseName property. The file contains the database and is opened or created when the connection is opened successfully. Listing 13-2. Connecting to an SQLite file QSqlDatabase db = QSqlDatabase::addDatabase( "QSQLITE" ); db.setDatabaseName( "testdatabase.db" ); if( !db.open() ) { qDebug() << db.lastError(); qFatal( "Failed to connect." ); }

int answer = 42;

or this:

System.Int32 answer = 42;