Continue in nested while loops

In this code sample, is there any way to continue on the outer loop from the catch block?

while
{
   // outer loop

   while
   {
       // inner loop
       try
       {
           throw;
       }
       catch 
       {
           // how do I continue on the outer loop from here?
           continue;
       }
   }
}

Solution 1:

UPDATE: This question was inspiration for my article on this subject. Thanks for the great question!

"continue" and "break" are nothing more than a pleasant syntax for a "goto". Apparently by giving them cute names and restricting their usages to particular control structures, they no longer draw the ire of the "all gotos are all bad all the time" crowd.

If what you want to do is a continue-to-outer, you could simply define a label at the top of the outer loop and then "goto" that label. If you felt that doing so did not impede the comprehensibility of the code, then that might be the most expedient solution.

However, I would take this as an opportunity to consider whether your control flow would benefit from some refactoring. Whenever I have conditional "break" and "continue" in nested loops, I consider refactoring.

Consider:

successfulCandidate = null;
foreach(var candidate in candidates)
{
  foreach(var criterion in criteria)
  {
    if (!candidate.Meets(criterion))
    {  // TODO: no point in continuing checking criteria.
       // TODO: Somehow "continue" outer loop to check next candidate
    }
  }
  successfulCandidate = candidate;
  break;
}
if (successfulCandidate != null) // do something

Two refactoring techniques:

First, extract the inner loop to a method:

foreach(var candidate in candidates)
{
  if (MeetsCriteria(candidate, criteria))
  { 
      successfulCandidate = candidate;
      break;
  }
}

Second, can all the loops be eliminated? If you are looping because you are trying to search for something, then refactor it into a query.

var results = from candidate in candidates 
              where criteria.All(criterion=>candidate.Meets(criterion))
              select candidate;
var successfulCandidate = results.FirstOrDefault();
if (successfulCandidate != null)
{
  do something with the candidate
}

If there are no loops then there is no need to break or continue!

Solution 2:

    while
    {
       // outer loop

       while
       {
           // inner loop
           try
           {
               throw;
           }
           catch 
           {
               // how do I continue on the outer loop from here?
               goto REPEAT;
           }
       }
       // end of outer loop
REPEAT: 
       // some statement or ; 
    }

Problem solved. (what?? Why are you all giving me that dirty look?)

Solution 3:

You can use a break; statement.

while
{
   while
   {
       try
       {
           throw;
       }
       catch 
       {
           break;
       }
   }
}

Continue is used to jump back to the top of the current loop.

If you need to break out more levels than that you will either have to add some kind of 'if' or use the dreaded/not recommended 'goto'.

Solution 4:

Swap the try/catch structure with the inner while loop:

while {
  try {
    while {
      throw;
    }
  }
  catch {
    continue;
  }
}