Programming Microsoft Visual Basic .NET/Programming Microsoft Visual Basic .NET (Microsoft Press)(X08-78517)(2002).bin/03 control flow and error handling/controlflowdemo/mainmodule1.vb

Text File | 2002-03-20 | 8.4 KB | 251 lines

Module MainModule

    Sub Main()
        ' Run one of the Textxxxx procedures below by uncommenting only one statement

        'TestReturn()
        'TestCallByRef()
        'TestArrayByVal()
        'TestArrayByRef()
        'TestParamArray()
        'TestLabelProblem()
        'TestFindWindow()
        'TestVBFunctions()

        ' These statements are usuful when running inside Visual Studio.NET
        Console.WriteLine("")
        Console.WriteLine(">>> Press Enter to terminate the program <<<")
        Console.ReadLine()
    End Sub

    ' this procedure tests the Return performance compared to traditional
    ' way to return from a procedure

    Sub TestReturn()
        Dim start As Date
        Dim i As Integer
        Dim res As Integer

        start = Now
        For i = -10000000 To 10000000
            res = TestFunction_One(i)
        Next
        Console.WriteLine("Using local variable: {0} secs.", Now.Subtract(start))

        start = Now
        For i = -10000000 To 10000000
            res = TestFunction_Two(i)
        Next
        Console.WriteLine("Using Return statement: {0} secs.", Now.Subtract(start))
    End Sub

    ' auxiliary functions

    Function TestFunction_One(ByVal x As Integer) As Integer
        If x > 0 Then
            TestFunction_One = 1
        Else
            TestFunction_One = -1
        End If
    End Function

    Function TestFunction_Two(ByVal x As Integer) As Integer
        If x > 0 Then
            Return 1
        Else
            Return -1
        End If
    End Function

    ' this procedure demonstrates that array passed ByVal can be
    ' modified by the called procedure

    Sub TestArrayByVal()
        Dim anArray() As Integer = {0, 1, 2, 3, 4}
        ' Pass the array by value to a procedure.
        Call ArrayProcByval(anArray)
        ' Prove that the array has been modified.
        Console.WriteLine(anArray(3))     ' => 300
    End Sub

    ' A procedure that modifies its array argument's elements
    Sub ArrayProcByval(ByVal arr() As Integer)
        Dim i As Integer
        For i = 0 To UBound(arr)
            arr(i) = arr(i) * 100
        Next
    End Sub

    ' this procedure shows the difference in passing an array byval or byref

    Sub TestArrayByRef()
        Dim byvalArray(10) As Integer
        Dim byrefArray(10) As Integer
        ' Pass both arrays to the procedure.
        Call ArrayProcByRef(byvalArray, byrefArray)
        ' Check which array has been affected by the ReDim.
        Console.WriteLine(UBound(byvalArray))   ' => 10 (not modified)
        Console.WriteLine(UBound(byrefArray))   ' => 100 (modified)
    End Sub

    Sub ArrayProcByRef(ByVal arr() As Integer, ByRef arr2() As Integer)
        ' Change the size of both arrays.
        ReDim arr(100)
        ReDim arr2(100)
    End Sub

    ' this procedure tests the ParamArray keyword

    Sub TestParamArray()
        Console.WriteLine(Sum(3, 1, 5))            ' => 9

        Console.WriteLine(Sum2(3, 1, 5))           ' => 9

        Console.WriteLine(MinValue(3, 1, 5))       ' => 1
    End Sub

    ' sum all the arguments
    Function Sum(ByVal ParamArray args() As Integer) As Integer
        Dim sumResult, index As Integer
        For index = 0 To UBound(args)
            sumResult += args(index)
        Next
        Sum = sumResult
    End Function

    ' alternative, more concise version
    Function Sum2(ByVal ParamArray args() As Integer) As Integer
        Dim index As Integer
        For index = 0 To UBound(args)
            Sum2 = Sum2 + args(index)
        Next
    End Function

    ' this procedure shows that you can deal with a ParamArray argument
    ' as if it were a regular array

    Function MinValue(ByVal ParamArray args() As Object) As Object
        ' Sort the array, and then return its 1st element.
        System.Array.Sort(args)
        MinValue = args(0)
    End Function

    ' this procedure demonstrates a problem with procedures without any arguments:

    Sub TestLabelProblem()
        ' This code doesn't work as expected.
WriteHello: Console.WriteLine("World") ' => World

        ' This code works correctly.
        WriteHello() : Console.WriteLine("World") ' => Hello World
    End Sub

    Sub WriteHello()
        Console.Write("Hello ")
    End Sub

    ' API declares

    Private Declare Ansi Function FindWindow Lib "user32" Alias "FindWindowA" _
        (ByVal lpClassName As String, ByVal lpWindowName As String) As Integer
    Private Declare Function MoveWindow Lib "user32" Alias "MoveWindow" _
        (ByVal hWnd As Integer, ByVal x As Integer, ByVal y As Integer, _
        ByVal nWidth As Integer, ByVal nHeight As Integer, _
        ByVal bRepaint As Integer) As Integer

    ' NOTE: launch Notepad on an empty document before running this code.
    Sub TestFindWindow()
        Dim hWnd As Integer = FindWindow(Nothing, "Untitled - Notepad")
        If hWnd <> 0 Then MoveWindow(hWnd, 0, 0, 600, 300, 1)
    End Sub

    ' this procedure tests several functions in the Microsoft.VisualBasic namespaces

    Sub TestVBFunctions()
        Dim s1 As String = "abc"
        Dim s2 As String = "ABC"
        Dim res As String

        ' Compare two strings in case-insensitive mode.
        If StrComp(s1, s2, CompareMethod.Text) = 0 Then res = "Equal"
        Console.WriteLine("res = " & res)

        ' This statements prints a line of 50 dashes.
        Console.WriteLine(StrDup(50, "-"))

        ' the GetChar method
        Console.WriteLine(GetChar("ABCDE", 2))     ' => B

        ' The natural logarithm of 10
        Console.WriteLine(Math.Log(10))            ' => 2.30258509299405
        ' Two ways to evaluate he decimal logarithm of 1000
        Console.WriteLine(Math.Log(1000, 10))      ' => 3
        Console.WriteLine(Math.Log10(1000))        ' => 3

        Console.WriteLine(Math.Min(1.5, 0.7))      ' => 0.7
        Console.WriteLine(Math.Max(99, 87))        ' => 99

        Console.WriteLine(Math.Floor(-1.5))        ' => -2
        Console.WriteLine(Math.Ceiling(2.5))       ' => 3

        Console.WriteLine(Math.IEEERemainder(2, 1.5))      ' => 0.5

        ' date-time functions

        ' Get the date two weeks from now.
        Dim newDate As Date = DateAdd(DateInterval.WeekOfYear, 2, Now())
        Console.WriteLine(newDate)

        ' Evaluate days left to December 31 of current year.
        Dim days As Long = DateDiff(DateInterval.Day, Today, _
            DateSerial(Year(Today), 12, 31))
        Console.WriteLine(days)

        ' abbreviated month name
        Console.WriteLine(MonthName(1, True))       ' => Jan

        ' display a msgbox

        Dim userChoice As MsgBoxResult
        userChoice = MsgBox("Want to run Notepad", MsgBoxStyle.Question Or MsgBoxStyle.YesNo)
        If userChoice = MsgBoxResult.Yes Then
            ' run notepad and wait until it returns, or until 10 secs. have elapsed
            Dim taskID As Long = Shell("notepad", AppWinStyle.NormalFocus, True, 10000)
            If taskID = 0 Then
                Console.WriteLine("Notepad has been closed within 10 seconds.")
            Else
                Console.WriteLine("Notepad is still running after 10 seconds.")
            End If
        End If

        ' read a text file
        Dim handle As Integer = FreeFile()
        ' open a file for input
        FileOpen(handle, "C:\autoexec.bat", OpenMode.Input, OpenAccess.Read)
        ' read the entire file in one operation
        Dim fileText As String = InputString(handle, CInt(LOF(handle)))
        ' close the file
        FileClose(handle)
        Console.WriteLine(fileText)

        ' Display the description associated to error code 9.
        Console.WriteLine(ErrorToString(9))   ' => Subscript out of Range

        Dim x As Integer
        Console.WriteLine(System.Runtime.InteropServices.Marshal.SizeOf(x))      ' => 4

        Console.WriteLine(SystemTypeName("Long"))        ' => System.Int64
        Console.WriteLine(VbTypeName("System.Int16"))    ' => Short

        ' The new IsReference function returns True if the argument evaluates to a reference type,
        '  or False if it is a value type:
        Dim n As Integer = 1
        Dim s As String = "ABC"
        Console.WriteLine(IsReference(n))    ' => False
        Console.WriteLine(IsReference(s))    ' => True
    End Sub

End Module