Breaking/exit nested for in vb.net

Question

How do I get out of nested for or loop in vb.net?

I tried using exit for but it jumped or breaked only one for loop only.

How can I make it for the following:

for each item in itemList
     for each item1 in itemList1
          if item1.text = "bla bla bla" then
                exit for
          end if
     end for
end for

What VB really needs is an `Exit For item` variant of the statement, similar to `Next item`. In the "good old days" you could explicitly `Next` the outer loop. Today, VB gives an error. Of course, it is more "constructive" to `Exit For` instead. — ysap, Aug 07 '18 at 11:34

Heinzi · Accepted Answer · 2011-03-15T13:55:11.840

Unfortunately, there's no exit two levels of for statement, but there are a few workarounds to do what you want:

Goto. In general, using goto is considered to be bad practice (and rightfully so), but using goto solely for a forward jump out of structured control statements is usually considered to be OK, especially if the alternative is to have more complicated code.
```
For Each item In itemList
    For Each item1 In itemList1
        If item1.Text = "bla bla bla" Then
            Goto end_of_for
        End If
    Next
Next

end_of_for:
```

Dummy outer block

Do
    For Each item In itemList
        For Each item1 In itemList1
            If item1.Text = "bla bla bla" Then
                Exit Do
            End If
        Next
    Next
Loop While False

or

Try
    For Each item In itemlist
        For Each item1 In itemlist1
            If item1 = "bla bla bla" Then
                Exit Try
            End If
        Next
    Next
Finally
End Try

Separate function: Put the loops inside a separate function, which can be exited with return. This might require you to pass a lot of parameters, though, depending on how many local variables you use inside the loop. An alternative would be to put the block into a multi-line lambda, since this will create a closure over the local variables.

Boolean variable: This might make your code a bit less readable, depending on how many layers of nested loops you have:

Dim done = False

For Each item In itemList
    For Each item1 In itemList1
        If item1.Text = "bla bla bla" Then
            done = True
            Exit For
        End If
    Next
    If done Then Exit For
Next

Can't say that any of those are better than the `goto` other than the function if it actually makes sense. — Chris Marisic, Aug 20 '14 at 21:15
I am going to use that `goto` in a big project just to remember my programming days in qbasic, ah such innocent times. otherwise i would go for a dummy do. — Sharky, Mar 03 '15 at 10:26
I prefer the `Try` / `Exit Try` approach, but I am no fan of the `goto` option. — JohnH, May 25 '16 at 13:34
Note that the "Boolean variable" method requires multiple variables and tests as nesting level gets deeper. This becomes fugly... — ysap, Aug 07 '18 at 11:30
@ysap - In my experience, its rare to need multiple boolean variables. Typically, there is a single exit condition (e.g. "done") that once it is encountered, all loop levels should be exited. Nevertheless, I prefer making a separate method, and using "Return" - this cleanly encapsulates the nested construct. — ToolmakerSteve, May 26 '19 at 20:32

score 17 · Answer 2 · answered Mar 15 '11 at 13:22

17

Put the loops in a subroutine and call return

answered Mar 15 '11 at 13:22

Tobias Schittkowski

2,221
2
16
25

1

It's worth noting that there is overhead associated with such a call that is not present in the simpler `goto` solution. Of course, if the code is reusable it should be in a function already anyway. – Dan Bechard Mar 02 '16 at 22:11
How can it be an overhead? @Dan – Altiano Gerung May 02 '18 at 03:02
@AltianoGerung Well, my comment above assumes the compiler doesn't optimize and inline the function call. All function calls (assuming they're not inlined by the compiler) have the overhead of the prologue and epilogue to update the base stack pointer (as well as do other things like call destructors and do garbage collection if the language supports it). This is often minutia in the grand scheme of things, but does exist and can quickly become apparent in tight loops. https://en.wikipedia.org/wiki/Function_prologue – Dan Bechard May 07 '18 at 21:23
@Dan Well, that's beyond me LOL. I think with my use cases and how technology improve over time, I will never need to worry about it. – Altiano Gerung May 08 '18 at 01:26
2

@AltianoGerung If there's anything experience has taught me, it's that with enough scale, even the smallest of problems become big enough to matter. As always, profile before you make any assumptions. :) – Dan Bechard May 09 '18 at 21:30

score 7 · Answer 3 · edited Aug 07 '18 at 11:29

7

For i As Integer = 0 To 100
    bool = False
    For j As Integer = 0 To 100
        If check condition Then
            'if condition match
            bool = True
            Exit For 'Continue For
        End If
    Next
    If bool = True Then Continue For
Next

edited Aug 07 '18 at 11:29

ysap

7,723
7
59
122

answered May 01 '17 at 06:02

Hitesh Paliwal

79
1
2

Do not use this. Its behavior is wrong. Instead see accepted answer's "boolean variable" solution from six years earlier. If it were a new approach, I would explain what makes it behave incorrectly, but its not worth doing so, as the approach was already correctly shown in that earlier answer. – ToolmakerSteve May 26 '19 at 20:42

score 3 · Answer 4 · answered May 29 '12 at 14:52

3

Make the outer loop a while loop, and "Exit While" in the if statement.

answered May 29 '12 at 14:52

Andrew Thomas

2,482
3
25
29

This does the exact same thing as `goto` with more instructions, more verbosity and more indentation. What's the point? – Dan Bechard Mar 02 '16 at 22:15

Cesar · Answer 5 · 2015-05-20T18:16:23.020

3

I've experimented with typing "exit for" a few times and noticed it worked and VB didn't yell at me. It's an option I guess but it just looked bad.

I think the best option is similar to that shared by Tobias. Just put your code in a function and have it return when you want to break out of your loops. Looks cleaner too.

For Each item In itemlist
    For Each item1 In itemlist1
        If item1 = item Then
            Return item1
        End If
    Next
Next

edited May 20 '15 at 18:16

answered Feb 06 '13 at 04:04

Cesar

2,229
1
22
20

No, multiple "Exit For"s *does not* result in the desired behavior. The first one exits the *first* loop, additional ones are never reached, so have no effect. Other than that suggestion, you seem to have simply repeated earlier answers. – ToolmakerSteve May 26 '19 at 20:47

score 0 · Answer 6 · edited Mar 23 '23 at 01:56

0

If I want to exit a for-to loop, I just set the index beyond the limit:

  For i = 1 To max
    some code
    if this(i) = 25 Then i = max + 1
    'some more code...
  Next

edited Mar 23 '23 at 01:56

Rohad Bokhar

104
9

answered Apr 10 '19 at 15:30

Poppa Mintin

1

I recommend showing how this applies to this question. Take the code from the question, and edit it to use this approach. – ToolmakerSteve May 26 '19 at 20:44

score 0 · Answer 7 · answered Sep 10 '21 at 04:40

0

Insert a boolean value check in your loop:
If MyBreak Then
Exit Sub
End If
Where MyBreak is toggled by a button or label clicked.

answered Sep 10 '21 at 04:40

YaoChen Aan

19
2

Breaking/exit nested for in vb.net

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