в 16:40, 26 мая 2010

2010-05-26T16:40:30Z

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2010-05-26T12:54:30Z

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==Block scope==

<source lang="vbnet">Option Strict On
Public Class BlockScope
Public Shared Sub Main()

For outerLoop As Integer = 0 to 10000
For innerLoop As Integer = 0 to 10
Dim blockVar As Integer
blockVar += 1
If blockVar Mod 1000 = 0 Then
Console.WriteLine(blockVar)
End If
Next
Next

End Sub
End Class</source>
<pre class=codeResult>1000
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...</pre>

==Define variable inside If statement==

<source lang="vbnet">public class Test
public Shared Sub Main
Dim manager As Boolean = True
If manager Then Dim txt As String = "M" : Console.WriteLine(txt) Else _
Dim txt As String = "E" : Console.WriteLine(txt)
End Sub
End class</source>
<pre class=codeResult>M</pre>

==Demonstrates scope rules and instance variables==

<source lang="vbnet">Public Class Tester
" instance variable can be used anywhere in class
Dim Shared value As Integer = 1
" demonstrates class scope and block scope
Public Shared Sub Main
Dim value As Integer = 5
Console.WriteLine("local variable value in" & _
" FrmScoping_Load is " & value )
MethodA() " MethodA has automatic local value
MethodB() " MethodB uses instance variable value
MethodA() " MethodA creates new automatic local value
MethodB() " instance variable value retains its value
Console.WriteLine("local variable " & _
"value in FrmScoping_Load is " & value )
End Sub
" automatic local variable value hides instance variable
Shared Sub MethodA()
Dim value As Integer = 25 " initialized after each call
Console.WriteLine("local variable " & _
"value in MethodA is " & value & " after entering MethodA" )
value += 1
Console.WriteLine("local variable " & _
"value in MethodA is " & value & " before exiting MethodA" )
End Sub
" uses instance variable value
Shared Sub MethodB()
Console.WriteLine("instance variable" & _
" value is " & value & " after entering MethodB" )
value *= 10
Console.WriteLine("instance variable " & _
"value is " & value & " before exiting MethodB" )
End Sub
End Class</source>
<pre class=codeResult>local variable value in FrmScoping_Load is 5
local variable value in MethodA is 25 after entering MethodA
local variable value in MethodA is 26 before exiting MethodA
instance variable value is 1 after entering MethodB
instance variable value is 10 before exiting MethodB
local variable value in MethodA is 25 after entering MethodA
local variable value in MethodA is 26 before exiting MethodA
instance variable value is 10 after entering MethodB
instance variable value is 100 before exiting MethodB
local variable value in FrmScoping_Load is 5</pre>

==Function local variables==

<source lang="vbnet">Module Module1
Sub F()
Dim Name As String = "www.vbex.ru"
Dim Price As Double = 17.45
Dim I As Integer = 1001
Console.WriteLine("In F")
Console.WriteLine("Name: " & Name)
Console.WriteLine("Price: " & Price)
Console.WriteLine("I: " & I)
End Sub
Sub FF()
Dim Name As String = "string"
Dim Price As Double = 49.99
Dim I As Integer = 0
Console.WriteLine("In FF")
Console.WriteLine("Name: " & Name)
Console.WriteLine("Price: " & Price)
Console.WriteLine("I: " & I)
End Sub
Sub Main()
F()
Console.WriteLine()
FF()
End Sub
End Module</source>
<pre class=codeResult>In F
Name: www.vbex.ru
Price: 17.45
I: 1001
In FF
Name: string
Price: 49.99
I: 0</pre>

==Local variable shadows global variable with the same name==

<source lang="vbnet">Module Module1
Dim Counter As Integer
Sub BigLoop()
For Counter = 1000 To 1005 " Use global Counter
Console.Write(Counter & " ")
Next
End Sub
Sub LittleLoop()
Dim Counter As Integer
For Counter = 0 To 5 " Use local Counter
Console.Write(Counter & " ")
Next
End Sub
Sub Main()
Counter = 100
Console.WriteLine("Starting Counter: " & Counter)
BigLoop()
Console.WriteLine("Counter after BigLoop: " & Counter)
LittleLoop()
Console.WriteLine("Counter after LittleLoop: " & Counter)
If (Counter > 1000) Then
Dim Counter As Integer = 0
Console.WriteLine("Counter in If statement: " & Counter)
End If
Console.WriteLine("Ending Counter: " & Counter)
End Sub
End Module</source>
<pre class=codeResult>Starting Counter: 100
1000 1001 1002 1003 1004 1005 Counter after BigLoop: 1006
0 1 2 3 4 5 Counter after LittleLoop: 1006
Counter in If statement: 0
Ending Counter: 1006</pre>

==Module global variable==

<source lang="vbnet">Module Module1
Sub Main()
For intLoopIndex As Integer = 0 To 5
System.Console.WriteLine(Tracker())
Next intLoopIndex
End Sub
Dim intCount As Integer
Function Tracker() As Integer
intCount += 1
Return intCount
End Function
End Module</source>
<pre class=codeResult>1
2
3
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6</pre>

==Sub scope==

<source lang="vbnet">public class Test
public Shared Sub Main
DisplayHowardsName()
DisplayStephsName()
End Sub
Shared Sub DisplayStephsName()
Dim myName As String
myName = "A"
Console.WriteLine(myName)
End Sub
Shared Sub DisplayHowardsName()
Dim myName As String
myName = "B"
Console.WriteLine(myName)
End Sub

End class</source>
<pre class=codeResult>B
A</pre>

==Variable block scope==

<source lang="vbnet">public class Test
public Shared Sub Main
For i As Integer = 1 To 5
Dim j As Integer = 3
If i = j Then
Dim M As Integer = i + j
Console.WriteLine("M: " & M)
Else
Dim N As Integer = i * j
Console.WriteLine("N: " & N)
End If
Dim k As Integer = 123
Console.WriteLine("k: " & k)
Next i
End Sub
End class</source>
<pre class=codeResult>N: 3
k: 123
N: 6
k: 123
M: 6
k: 123
N: 12
k: 123
N: 15
k: 123</pre>

==Variable scope in try catch statement==

<source lang="vbnet">public class Test
public Shared Sub Main

Try
Dim i As Integer = CInt("bad value")
Catch ex As InvalidCastException
Dim txt As String = "InvalidCastException"
Console.WriteLine(txt)
Catch ex As Exception
Dim txt As String = "Exception"
Console.WriteLine(txt)
End Try
End Sub
End class</source>
<pre class=codeResult>InvalidCastException</pre>

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в 16:40, 26 мая 2010

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