Control Statements in VB.NET: Part 1
In this article I will explain your about different control statements in VB.NET.
Control statements give you additional means to control the processing within the applications you develop. This section explores the syntax and function of the if, select case, do-while, foreach, goto, exit, continue, and return statements.
If-then-else
The if statement has three forms: single selection, if-then-else selection, and multicase selection. Listing 5.23 contains an example of each form.
Listing 5.23: If-Else-ElseIf Example 1
'single selection
If i > 0 Then
Console.WriteLine("The number {0} is positive", i)
End If
'if-then-else selection
If i > 0 Then
Console.WriteLine("The number {0} is positive", i)
Else
Console.WriteLine("The number {0} is not positive", i)
End If
'multicase selection
If i = 0 Then
Console.WriteLine("The number is zero")
ElseIf i > 0 Then
Console.WriteLine("The number {0} is positive", i)
Else
Console.WriteLine("The number {0} is negative", i)
End If
The variable i is the object of evaluation here. The expression in an if statement must resolve to a boolean value type.
' Compiler Error
If 1 Then
Console.WriteLine("The if statement executed")
End If
Console.ReadLine()
When the VB.NET compiler compiles the preceding code, it generates the error "Constant value 1 cannot be converted to bool."
Listing 5.24 shows how conditional or (OrElse) and conditional and (AndAlso) operators are used in the same manner.
Listing 5.24: If-Then-Else Example 2
'Leap year
Dim year As Integer = 1974
If (year Mod 4 = 0 AndAlso year Mod 100 <> 0) OrElse year Mod 400 = 0 Then
Console.WriteLine("The year {0} is leap year ", year)
Else
Console.WriteLine("The year {0} is not leap year ", year)
End If
Switch
From the example in Listing 5.25, you can see that the select case is similar to an if-else ifelse if-else form of an if statement.
Listing 5.25: Switch Example 1
Dim day As String = "Monday"
Console.WriteLine("enter the day :")
day = Console.ReadLine()
Select Case day
Case "Mon"
Exit Select
Case "Monday"
Console.WriteLine("day is Monday: go to work")
Exit Select
Case Else
Console.WriteLine("default")
Exit Select
End Select
Select Case strVal1
Case "reason1"
goto case "reason2"
' this is a jump to mimic fall-through
Case "reason2"
intOption = 2
Exit Select
Case "reason 3"
intOption = 3
Exit Select
Case "reason 4"
intOption = 4
Exit Select
Case "reason 5"
intOption = 5
Exit Select
Case Else
intOption = 9
Exit Select
End Select
Conclusion
Hope this article would have helped you in understanding control statements in VB.NET.