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Loops
For Loop
The For loop is the most popular loop. For loops enables us to execute a series of
expressions multiple numbers of times. The For loop needs a loop index, which
counts the number of loop iterations as the loop executes.
For Loop Sample
The following code demonstrates for loop.
Private Sub ForLoop_Click(ByVal sender As System.Object, ByVal e_
As System.EventArgs) Handles ForLoop.Click
'assuming you have a button named ForLoop
Dim i As Integer
For i = 1 To 5
Response.Write("Welcome to ASP.NET")
Next i
End Sub
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Do Loop
The Do loop can be used to execute a fixed block of statements indefinite number of
times. The Do loop keeps executing it's statements while or until the condition is
true. Two keywords while and until can
be used with the do loop. The Do loop also supports an Exit Do statement
which makes the loop to exit at any moment.
Do Loop Sample
The following code demonstrates Do loop.
Private Sub DoWhile_Click(ByVal sender As System.Object, ByVal e_
As System.EventArgs) Handles DoWhile.Click
'assuming you have a button named DoWhile
Dim x As Integer
x = 0
Do Until x = 10
x = x + 1
Response.Write(x)
Loop
End Sub
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If....Then....Else Statement
If conditional expression is one of the most useful control structures which allows
us to execute a expression if a condition is true and execute a different expression
if it is False. If the condition is true the statements following the Then keyword
will be executed, else the statements following the ElseIf will be checked and if
true, will be executed, else the statements in the else part will be executed.
If Then Sample
The following code demonstrates If..Then..Else conditional statement. It asks the
user to enter a number between 1 and 3 in a textbox and checks for the number entered
using the If..Then..Else statement and displays some text if the condition is
true.
Private Sub IfThen_Click(ByVal sender As System.Object, ByVal e_
As System.EventArgs) Handles IfThen.Click
If CInt(TextBox1.Text) = 1 Then
Label1.Text = "You entered" & CInt(TextBox1.Text)
ElseIf CInt(TextBox1.Text) = 2 Then
Label1.Text = "You entered" & CInt(TextBox2.Text)
ElseIf CInt(TextBox1.Text) = 3 Then
Label1.Text = "You entered" & CInt(TextBox2.Text)
Else
Label1.Text = "You entered another number"
End If
End Sub
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Select Case Statement
Select Case is similar to If..Then..Else statement. Select Case allows us to do various
comparisions against one variable that we use throughout the whole statement. Select
Case is cleaner and easier to understand if you are continually comparing against
one variable.
Select Case Sample
The following sample asks the user to enter a vowel in a textbox and checks the value
entered using the the Select Case statement and if true displays some text.
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e_
As System.EventArgs) Handles Button1.Click
Select Case TextBox1.Text
Case "a"
Label1.text = "You entered A"
Case "e"
Label1.Text = "You entered E"
Case "i"
Label1.Text = "You entered I"
Case "o"
Label1.Text = "You entered O"
Case "u"
Label1.Text = "You entered U"
End Select
End Sub
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Live Code Demo
If...Then...Else
Enter a number between 1 and 3
Select Case
Enter a vowel and click the button
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