6: Data and Data Types in Visual Basic .NET

Creator QR-Code in Visual Basic .NET 6: Data and Data Types

6: Data and Data Types
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MsgBox("The board is " & _ (ticTacToeBoard.GetUpperBound(0) + 1) & _ " by " & (ticTacToeBoard.GetUpperBound(1) + 1))
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Initializing Arrays
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Once you ve declared your array elements, you can store and retrieve elements whenever you need. It s also possible to store elements in your array right at declaration time. The list of new array elements appears in a set of curly braces.
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Dim squares( ) As Integer = {0, 1, 4, 9, 16, 25}
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You must leave out the lower and upper bound specifications when creating an array in this way. The squares array shown here will have elements numbered 0 to 5.
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Nullable Types
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Value types are hard-working variables, maintaining their data values throughout their lives. Reference types work hard, too, but they can be filled with Nothing and get a little rest time. This difference has long been a thorn in the side of value types. Is it too much to ask to give these working-class variables a little down time Well, Microsoft has heard this plea, and starting with Visual Basic 2008, value types can now be assigned with Nothing. These new nullable types are essential when you want to have an undefined state for a standard value type (especially useful when working with database fields). Consider this class that manages employee information:
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Public Class Employee Public Name As String Public HireDate As Date Public FireDate As Date Public Sub New(ByVal employeeName As String, _ ByVal dateHired As Date) Me.Name = employeeName Me.HireDate = dateHired End Sub End Class
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This class works well, except that FireDate is not really correct. By default, FireDate will be set to January 1, 1, at midnight, and you can use that date as your never fired date. But what happens if your company really did fire someone just at that moment, two thousand years ago To resolve this issue, nullable types let you assign and retrieve Nothing from value type variables. These vitamin-enriched value types are declared using a special questionmark syntax.
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' ----- Either of these two statements will work. Public FireDate As Date Public FireDate2 As Date
Nullable Types |
I prefer the first syntax, with the question mark added to the data type. But either statement will work. Once it s declared, a value type can take either standard data or Nothing.
FireDate = Nothing FireDate = #7/18/2008# If (FireDate Is Nothing) Then...
There is a special syntax when defining your own custom value types as nullable, but since it uses the generics Visual Basic feature, I ll wait to introduce it until 16.
Common Visual Basic Functions
This final section includes a brief listing of the functions built into the Visual Basic language, many of which you will use regularly in your applications. Also listed here are some members of the Framework Class Library (FCL) that replicate features that were part of the Visual Basic language before .NET, but were moved into the framework for more general access. For the exact syntax required to use these functions, access the Visual Studio online help.
Conversion Functions
The conversion functions allow you to convert data of one Visual Basic data type to another. It s not a free-for-all, so don t go converting the string "hello" to an integer and expect it to work. But converting numbers from one numeric type to another, or converting numbers between string and numeric types, generally works just fine. All of these statements (except CType) have the same basic syntax:
dest = CXxxx(source)
where source is the value to be converted by CXxxx. You don t have to assign the result to a variable; you can use the result anywhere you would use a similar literal or variable value. Table 6-9 lists the built-in conversion functions.
Table 6-9. Visual Basic conversion functions Function
CBool CByte CChar CDate CDbl CDec
Description Converts a value to a Boolean. Converts a value to a Byte. Converts a value to a Char. If the source value is a string, only the first character is converted. Converts a value to a Date. If the source value is a string, it must be in a valid date or time format. Converts a value to a Double. Converts a value to a Decimal.
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