Switch case to break an outer loop?

Question

This isn't a specific problem that I actually am trying to implement, but it ocurred to me that I do not know how to do this, so I will give a simple example to illustrate:

Suppose we have a while loop containing a switch statement, for instance:

while(some_cond){
    switch(some_var){
        case 1:
            foo();
            break;
        case 2:
            bar();
            break;
    }
}

what would we do if we wanted to break out of the while loop in case 1, say?

We can't do break; break;, since the second will never happen.

We also can't do break *un*conditionally in the while loop, since this would happen in any case.

Do we have no choice but to if (some_var == 1) break; in the while loop, or else append && !flag) to the while condition, and set flag = 1?

"What would we do if we wanted to break out of the loop in case 1?" Redesign the code cleanly. — James Kanze, Feb 12 '14 at 17:49
@jameskanze a) that's what I'm asking a suggestion for; b) I was hoping for input on how to do it in any case. — OJFord, Feb 12 '14 at 17:51
@RikayanBandyopadhyay There's no problem in this case, but I'm not implementing this code. I was just giving a basic example, I wanted a general solution like the `goto` and `continue` provided. — OJFord, Feb 12 '14 at 18:14
Using `if (some_var == 1) break;` is way better than using `goto` though. — HelloWorld123456789, Feb 12 '14 at 18:16
Okay, it seems like the consensus from this Q, and @herohuyongtao's dupe link, is that we should avoid the situation arising. Which I will do. I should have made it clearer that I haven't run in to this problem - it just occurred to me as something I didn't know how to do, and wanted to learn. — OJFord, Feb 12 '14 at 18:20

score 3 · Answer 1 · answered Feb 12 '14 at 18:02

Various options, in approximate order of tastefulness:

Move the loop into a separate function. Use return to stop looping.
Replace while(1) with while(looping) and set to false to stop looping. Use continue if you need to skip the rest of the current iteration.
Use goto to jump past the end of the loop. How bad can it be?
Surround the loop with a try block, and throw something to stop looping.

herohuyongtao · Answer 2 · 2014-02-12T18:07:12.117

1

You can use goto (don't go too wild with goto though).

while ( ... ) {
   switch( ... ) {
     case ...:
         goto exit_loop;

   }
}
exit_loop: ;

edited Feb 12 '14 at 18:07

answered Feb 12 '14 at 17:39

herohuyongtao

49,413
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2

Oh wow, didn't even know `goto` existed. Thanks. – OJFord Feb 12 '14 at 17:48
In *a lot* of places you'll be sent to jail, you won't pass *Go* and you won't receive $200 if you use `goto`s. – Vaillancourt Feb 12 '14 at 17:54
@AlexandreVaillancourt As long as I don't go wild with `goto`. :) – herohuyongtao Feb 12 '14 at 17:57

score 0 · Answer 3 · answered Feb 12 '14 at 18:04

0

Have your while use a variable modified within your loop.

bool shoulEnterLoop = true;
while(shoulEnterLoop ){
  switch(some_var){
    case 1:
      if ( !foo() )
        shoulEnterLoop = false;
      break;
    case 2:
      bar();
      break;
  }
}

answered Feb 12 '14 at 18:04

Vaillancourt

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Switch case to break an outer loop?

3 Answers3