CODEWITHSUNDEEP
c#loopsbreaknested-loops
Aaaron
Aaaron

Reputation: 11

How to break out of an inner loop back to an outer loop?

I have 4 entities"

ObjectA, ObjectB, ObjectC, ObjectD

foreach(ObjectA objectA in listObjectA)
if (relationAB)
  foreach(ObjectB objectB in listObjectB) 
  if (relationBC)   
    foreach(ObjectC objectC in listObjectC) 
    if (relationCD)   
      foreach(ObjectD objectD in listObjectD) 
        if (I found what I'm looking for)  
        Do something

So, when I will found what I wass looking for, I want to go to the first line, to the first for, but to the second element from the list. How can I do this? Whit goto?

Later Edit: This question is for C#.

P.S. Could you think a better way to do what I'm trying to do, whithout using 4 fors?

Upvotes: 1

Views: 1232

Answers (4)

T.E.D.
T.E.D.

Reputation: 44804

Well, since this is just a "programming languages" question, the general answer would be to use your language's facility for naming loops, and then put the proper name on the "break" statement.

Sadly, I don't think the current versions of C and C++ support such a thing, so you would indeed have to resort to a goto when using them. A good way to avoid that would be to put the loop you want to break out of into its own subroutine, and just do a return when you are done instead of a break. That's what I generally do when working in those poor languages.

Your revised example would be:

void find_whatever (/* probably pass in the lists or objects to search for*/)
  foreach(ObjectA objectA in listObjectA)
    if (relationAB)
      foreach(ObjectB objectB in listObjectB) 
        if (relationBC)   
          foreach(ObjectC objectC in listObjectC) 
            if (relationCD)   
              foreach(ObjectD objectD in listObjectD) 
                if (I found what I'm looking for)  
                Do something
                return;

Note: The tag was changed from "programming languages" to "C#". That was the right thing to do for the question, but a lot of people liked this answer so I'm not making major mods to it.

Upvotes: 7

Vladimir Ivanov
Vladimir Ivanov

Reputation: 43088

Better to use return in such cases.

Just put some of your inner for in a method and return from it when necessary. It will be much more readable then a chain of 

if (found) {
 break;
}

inside your loops.

Upvotes: 0

Skilldrick
Skilldrick

Reputation: 70819

The simplest option is to put it all in a function and use the return statement instead of the break statement.

Upvotes: 1

Cameron Skinner
Cameron Skinner

Reputation: 54276

Depending on the language, you can generally add break labels. I'd avoid this, however, and suggest the following:

function main() {
    foreach (ObjectA a in listA) {
        if (relationAB) {
            processA(a)
        }
    }
}

function processA(ObjectA a) {
    foreach (b) {
        foreach (c) {
            foreach (d) {
                if (found) {
                    doSomething();
                    return;
                }
            }
        }
    }
}

It can be hard to read code that has break labels and gotos. Breaking it into functions can make it easier to read and (probably) easier to write and debug.

Upvotes: 3

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