HTML clipboardAs you learn some control
statement in previous article here is part 2 of remaining controls statement.
Control statements give you
additional means to control the processing within the applications you develop.
This section explores the syntax and function of the do-while, foreach, goto,
exit, continue, and return statements.
While
The while loop allows the user to repeat a section of code until a guard
condition is met. Listing 5.27 presents a simple while loop designed to find out
the number of digits in a given value.
Listing 5.27: While Example
'find out the number of digits in a given number
Dim i As
Integer = 123
Dim count As
Integer = 0
Dim n As
Integer = i
'while loop may
execute zero times
While
i > 0
System.Threading.Interlocked.Increment(count)
i = i / 10
End While
Console.WriteLine("Number
{0} contains {1} digits.", n, count)
For a given number i = 123, the loop will
execute three times. Hence the value of the count is three at the end of the
while loop.
This example has one logical flaw. If the value of i is 0, the output of the
code will be "Number 0 contains 0 digits." Actually, the number 0 contains one
digit. Because the condition of the while loop i > 0 is false from the beginning
for the value i = 0, the while loop does not even execute one time and the count
will be zero. Listing 5.28 presents a solution.
Listing 5.28: Do Example
'find out the number of digits in a given number
Dim i As
Integer = 0
Dim count As
Integer = 0
Dim n As
Integer = i
Do
System.Threading.Interlocked.Increment(count)
i = i / 10
Loop While
i > 0
Console.WriteLine("Number
{0} contains {1} digits.", n, count)
The do-while construct checks the condition
at the end of the loop. Therefore, the do-while loop executes at least once even
though the condition to be checked is false from the beginning.
ForEach
The For Each statement allows the iteration of processing over the elements in
arrays and collections. Listing 5.31 contains a simple example.
Listing 5.31: For Each Example 1
'foreach loop
Dim a As
String() = {"Chirag",
"Bhargav", "Tejas"}
For Each
b As String
In a
Console.WriteLine(b)
Next
Listing 5.32 presents a slightly more complex version of the foreach loop.
Listing 5.32: ForEach Example 2
Dim intNumbers
As Int16()
= {4, 5, 6, 1, 2, 3, -2, -1, 0}
For Each
i As Int16
In intNumbers
System.Console.WriteLine(i)
Next
Each iteration queries the collection for a new value for i. As long as the
collection intNumbers returns a value, the value is put into the variable i and
the loop will continue. When the collection is fully traversed, the loop will
terminate.
GoTo
You can use the goto statement to jump to a specific segment of code, as shown
in Listing 5.33. You can also use goto for jumping to switch cases and default
labels inside switch blocks. You should avoid the overuse of goto because code
becomes difficult to read and maintain if you have many goto jumps within your
code.
Listing 5.33: GoTo Example
label1:
'...
If x = 0
Then
GoTo label1
End
If
Exit
The exit statement, used within for, while, and do-while blocks, causes
processing to exit the innermost loop immediately. When a break statement is
used, the code jumps to the next line following the loop block, as you'll see in
Listing 5.34.
Listing 5.34: Exit Example
While
True
'...
If x = 0
Then
Exit While
'...
End
If
End
While
Console.WriteLine("Exit")
Continue
The continue statement (shown in Listing 5.35) is used to jump to the end of the
loop immediately and process the next iteration of the loop.
Listing 5.35: Continue Example
While
True
'...
If x = 0
Then
x = 5
Continue While
End
If
'...
If x = 5
Then
Console.WriteLine("continue")
'...
End
If
End
While
Return
The return statement is used to prematurely return from a method. The return
statement can return empty or with a value on the stack, depending upon the
return value definition in the method (Listing 5.36 shows both). Void methods do
not require a return value. For other functions, you need to return an
appropriate value of the type you declared in the method signature.
Listing 5.36: Return Example
Sub
MyFunc1()
' ...
If x = 1
Then
Return
End If
' ...
End Sub
Function MyFunc2()
As Integer
' ...
If x = 2
Then
Return 1919
End If
' ...
End
Function
Conclusion
Hope this article would have helped you in understanding control statements in
VB.NET.