Understanding Loops

[formlesstree4 18]

In all programming languages, there are various ways to do a loop. Fortunately for you guys, I only care about how VB.net does these loops.

 

These are the common loops:

1. The Do Until Loop

Do Until <condition>
  'Stuff here
Loop

Basically, the loop will continue until the condition is met.

Example:

Dim x As Integer = 0I
Do Until x = 9
  x += 1
Loop

That loop will run until x = 9, and that will happen because I'm incrementing the Integer 'x' by 1 every time the loop goes through.

 

2. The Do While Loop

Do While <condition>
  'Stuff
Loop

This loop seems kind of redundant, because most things can be done with a Do Until Loop instead. The main difference is the Do Until Loop continues to run until the value is met, and the Do While Loop runs while the condition is met.

 

Here are some rather sad examples of the Do loops:

Dim conn As Boolean = False
'Do Until Loop
Do Until conn = True
  CheckForInternet()
Loop
'Do While Loop
Do While conn = False
  CheckForInternet()
Loop

Obviously, the call to 'CheckForInternet()' doesn't matter here. I can say that that call will make conn = True, or stay false.

The loops are actually the same result, it's just personal preference. You can also do this:

Dim conn As Boolean = False
Do
 CheckForInternet()
Loop While conn = False

Do
 CheckForInternet()
Loop Until conn = True

This actually will call the sub FIRST, then check if the condition applies, however this is hardly used and I don't see a good reason for that to even exist.

 

3. The For/For Each Loop

Here's a For example

Dim x As Integer = 0I
For i = 0 To 4
   x += 1
Next

The regular For loop will continue to process the inside for a set amount of time. In this example, it will loop 5 times (0 to 4) while adding 1 to the variable 'x' each time. These kinds of loops allow for you to run certain functions for a set amount of time. The For loop will also accept variables into its counter:

Dim x As Integer = 0I
Dim i As Integer = 3I
For i To i + 6
   x += 1
Next

As you can see, we can use 'i' as a predefined variable and tell the loop to run 6 + i times (which 6 + 3 = 9, so from 3 to 9, or 6 times), adding 1 to x each time. We can also even use the 'i' directly.

Dim x As Integer = 0I
Dim i As Integer = 3I
For i To i + 6
   x += i
Next

Whatever 'i' equals at this time will be added to the 'x' variable. This is a versatile loop.

 

Now, this is a For Each Loop:

'Let's say I have an array with 5 items
Dim y As String(4) 'From 0 to 4
For Each i As String In Y
   Messagebox.show(i)
Next

As you can see, using the 'i', we can tell VB.net to display the current string. This kind of loop can never have an IndexOutOfRange Exception because you are telling the loop to display each individual value in the Array of Strings.

 

If you have any questions about these loops, or want me to go into more details, please let me know!

 

That's all for now!

[Polraudio 122]

Wow i learned more about loops here than 3 weeks of class.

[formlesstree4 18]

Wow i learned more about loops here than 3 weeks of class.

That's quite sad & rather scary considering you're paying for your classes in College and you learned more about Loops here on a forum...

I feel special...