How to leave a while loop inside a foreach loop

Question

I have a while loop and inside this while loop I have a foreach loop.

Here I learned how to skip the currently interaction on a loop by using Continue; Return; Break. But I need to leave the while loop when i'm inside the foreach loop is that possible ?

I'm on a interaction inside of the foreach loop and I want to leave the foreach and go to the next interaction of the while. How May I do that ? Like so:

while (!reader.EndOfStream)  //COMEÇO DO WHILE
{
  ///Some Codes

  foreach(string s in checkedlistbox1.items)
        {
          switch(s)
           {
             case "1":
                if( 1 > 0)
                 {
                    ///HERE I WANT TO GO TO THE NEXT INTERACTION OF THE WHILE
                    ///When I use CONTINUE; HERE, I GO TO THE NEXT INTERACTION OF THE FOREACH. BUT I NEED TO GO TO THE NEXT OF THE WHILE.
                 }
           }
        }
}

Here's what I want do to: I'm reading a file.txt line by line, and writing a new one with these values and some others things... Some of these values may be required (seted by user), if a required fieldis empty, so I do nothing, and go to the next while interaction...

refer http://stackoverflow.com/questions/863172/how-can-i-break-out-of-two-nested-for-loops-in-objective-c, its similar to what you need — Cris, Feb 19 '13 at 13:11
it would be helpful if you posted some code with your loops and explain as to where you want to break and on what conditons. — Ravi Y, Feb 19 '13 at 13:11
@IlyaIvanov using `break` i go to the next interaction of the `switch`itself ;s I need to go to the next of the `while` — Ghaleon, Feb 19 '13 at 13:14
Why are you iterating over a stream and then iterating over a checkboxlist. Given what you are trying to do, the best answer may involve a refactor of your code. — Mike C., Feb 19 '13 at 13:31
This may help - http://blogs.msdn.com/b/ericlippert/archive/2010/01/11/continuing-to-an-outer-loop.aspx — JMK, Feb 19 '13 at 13:48

Adam K Dean · Accepted Answer · 2013-02-19T13:35:39.217

You need to break from the switch and then from the foreach, whilst having a variable set.

You can then check that variable to see whether you should continue to the next while iteration.

Do it like this:

while (!reader.EndOfStream)
{
    // Some Codes

    bool skipToNext = false;

    foreach (string s in checkedlistbox1.items)
    {
        switch (s)
        {
            case "1":
                if (1 > 0)
                {
                    skipToNext = true;
                    break;
                }
        }

        if (skipToNext) break;
    }

    // in the case of there being more code, you can now use continue
    if (skipToNext) continue;

    // more code
}

Example of this flow working

var list = new List<string> { "0", "1", "2" };
int a = 0, b = 2;

while (a++ < b)
{
    // Some Codes

    bool skipToNext = false;

    foreach (string s in list)
    {
        Debug.WriteLine("{0} - {1}", a, s);

        switch (s)
        {
            case "1":
                if (1 > 0)
                {
                    Debug.WriteLine("Skipping switch...");
                    skipToNext = true;
                    break;
                }
        }

        if (skipToNext)
        {
            Debug.WriteLine("Skipping foreach...");
            break;
        }
    }

    // in the case of there being more code, you can now use continue
    if (skipToNext)
    {
        Debug.WriteLine("Skipping to next while...");
        continue;
    }

    // more code
}

Outputs:

1 - 0
1 - 1
Skipping switch...
Skipping foreach...
Skipping to next while...
2 - 0
2 - 1
Skipping switch...
Skipping foreach...
Skipping to next while...

I don't want to leave the while just go to the next interaction of the while ;x Does this method do that — Ghaleon, Feb 19 '13 at 13:19
The First `if(skipToNext) break;` Continued to the next `foreach interaction`, just like it was doing before. How I go to the next while interaction ? ;\ — Ghaleon, Feb 19 '13 at 13:29
My bad man ! Sorry about that, I used `continue` instead of `break` hehe ;x Now it's working !! LikeABoss! I'll just make a final test and i'll give a feedback... — Ghaleon, Feb 19 '13 at 13:40

Lorenzo Dematté · Answer 2 · 2013-02-19T13:26:40.667

1) Yes, it is possible. It works.

 foreach() {
    while() {
       break; //leave the while
    }
    //... and continues from here
 }

2) Each while will end before the next foreach iteration, so the second question does not make much sense... Unless you mean starting the next while inside the foreach, in which case.. yes!

 foreach() {
    while() {
       ...
    }
    break; //will go to the next foreach iteration, i.e. starts a new while
 }

As for your code sample, a break in the point you mentioned in the comment will do what you need (exit the foreach, going naturally to the next while iteration).

EDIT: after you posted the example, it appears that your problem is not in the interaction between while and foreach, but in the switch: break is used as a keyword for both "go to the next iteration in the loop" and "finish this case and the switch".

The break will be seen by the compiler as a 'switch break'. You need to mimic the behavior by yourself:

    foreach(string s in checkedlistbox1.items)
    {
      bool dobreak = false;
      switch(s)
       {
         case "1":
            if( 1 > 0)
             {
                dobreak = true;
             }
             break; // exit the case
       }
       if (dobreak)
          break; // exits the for (it is a 'foreach-break')
    }

Oh, I see! Without the code, I got the other way around (foreach/while). Same reasoning apply, however — Lorenzo Dematté, Feb 19 '13 at 13:13
@Ghaleon I read your edit, the problem is the break (which will be paired to the switch, not foreach). I'll edit my answer — Lorenzo Dematté, Feb 19 '13 at 13:17

score 1 · Answer 3 · answered Feb 19 '13 at 13:12

1

bool dobreak = false;
while (!reader.EndOfStream && !dobreak )  //COMEÇO DO WHILE
{
  ///Some Codes

  foreach(string s in checkedlistbox1.items)
        {
          switch(s)
           {
             case "1":
                if( 1 > 0)
                 {
                    dobreak = true;
                    break;
                 }
           }
        }
}

answered Feb 19 '13 at 13:12

Cris

12,799
5
35
50

1

This will exit both the foreach and the while... I suspect the OP does not want to exit the while as well.. – Lorenzo Dematté Feb 19 '13 at 13:16
What is `OP` ? And I don't want to leave the `while` just go to the next `interaction of the while` ;x Does this method do that ? – Ghaleon Feb 19 '13 at 13:18
OP = Original Poster/Post (i.e. the person or message that started the thread) – Matthew Watson Feb 19 '13 at 13:21

score 0 · Answer 4 · answered Feb 19 '13 at 13:14

Not tested, but these are a few possible ways which should answer your question:

bool continueLooping = true;

string[] array = { "1", "2" };

while (continueLooping)
{
    foreach (string x in array)
    {
        // break out of foreach loop AND while loop
        if (x == "1")
        {
            continueLooping = false;
            break;
        }

        // go to next iteration of foreach loop
        if (x == "2")
        {
            continue;
        }

        // break out of foreach loop and continue while loop
        if (x == "3")
        {
            break;
        }
    }
}

score 0 · Answer 5 · answered Feb 19 '13 at 13:16

You need to break from your foreach and the while so something like this:

bool abort = false;
while (!reader.EndOfStream && !abort)  //COMEÇO DO WHILE
{
  ///Some Codes

  foreach(string s in checkedlistbox1.items)
        {
          switch(s)
           {
             case "1":
                if( 1 > 0)
                 {
                    ///HERE I WANT TO LEAVE TO THE NEXT INTERACTION OF THE WHILE
                    abort = true;
                    break;
                 }
           }

           if (abort)
           {
               break;
           }
    }
}

score 0 · Answer 6 · answered Feb 19 '13 at 13:16

I'm beginner in C#, but I suggest that you add another condition to the while loop that you can set yourself. Then, change it whenever is needed. For example:

MyKeyCondition = 0;

while(MainCondition||MyKeyCondition){

if(MyCheckCondition){
MyKeyCondition = 1;
}

}

Now, if you change your key condition, you can handle the while loop even if the main condition is not satisfied.

score 0 · Answer 7 · answered Feb 19 '13 at 13:18

0

May try goto;

while (true)
{
 foreach(string s in checkedlistbox1.items)
  {
   switch(s)
   {
     case "1":
        if( 1 > 0)
        {
          goto WhileOut;
        }
    }
  }
}
WhileOut:
      // some code

answered Feb 19 '13 at 13:18

yogi

19,175
13
62
92

Matthew Watson · Answer 8 · 2013-02-19T13:36:25.387

0

Often nested loops are an indication that a method should be split up.

In this example, it could make the code clearer. If you place the inner for loop into a separate method, you can make that method return a bool. Return true if you want the outer while loop to continue iterating; otherwise, return false if you want it to exit the while loop.

It would look something like this:

private void doSomething(StreamReader reader)
{
    while (!reader.EndOfStream)
    {
        // Some Codes...

        if (!processNextItem(reader))
        {
            break;
        }
    }
}

// Returns true if the caller should continue its while loop; false if it should exit it.

private bool processNextItem(StreamReader reader)
{
    foreach (string s in checkedlistbox1.items)
    {
        switch (s)
        {
            case "1":
                if (1 > 0)
                {
                    return false; // Return false to exit while loop.
                }
        }
    }

    return true; // Return true to continue while loop.
}

I'm not sure what you'd need to pass to processNextItem(); I've just passed reader as an example.

edited Feb 19 '13 at 13:36

answered Feb 19 '13 at 13:30

Matthew Watson

104,400
10
158
276

It looks very beautiful '-' I don't know... I'll try to do this, the problem is my code is very `big` now. I'll make some tests and as soon as I get a result i'll post here, and i'll keeping checking here. – Ghaleon Feb 19 '13 at 13:33
If your functions are very big, then that's even more reason to split them up. You'll get short-term-pain for a lot of long-term-gain. :) – Matthew Watson Feb 19 '13 at 13:47
Yeah, you right... I'm just afraid to screw all up trying to change =s i'll make a back-up and try ! – Ghaleon Feb 19 '13 at 14:05
Ah, well that's where your battery of unit tests come in! You run the unit tests after each refactoring change to ensure you didn't break anything. – Matthew Watson Feb 19 '13 at 15:10

How to leave a while loop inside a foreach loop

8 Answers8