C++: How to decide the loop to continue to?

Question

I have Nested do-while, while, and for loops.

Is there a way to decide which loop to "continue" to? A variety of solutions would be great (not only goto..) Thank you!

while (foo==true) // loop1
{

   do
   {
      for(int i=0; i<someNumber ; i++) // loop3
      {

         if( soo==1)
         {
             <CONTINUE_TO_LOOP1>
         }
         else if( soo==2 )
         {
             <CONTINUE_TO_LOOP2>
         }
         else if( soo==3 )
         {
             <CONTINUE_TO_LOOP3>
         }

      }

   } while (moo==true) //loop2    

}

continue will only bring you to the parent loop. It means to "loop3". — Farah, Dec 26 '14 at 10:00
Draw a flowchart on paper and find a way to avoid such a construction. — Jongware, Dec 26 '14 at 10:02
@Jessica `break` will you put to the next outer loop. There you may need another condition to decide `break` again, or to `continue`. — πάντα ῥεῖ, Dec 26 '14 at 10:03
I have seen code that used nested loops and which solved a similar issue using `goto` and without the usual mess associated with its use. As another alternative, you could write an iterator-like type which has encapsulates the looping operations and in return provides the values for `i`, `moo` and `foo`. The body of the loop would then just contain the innermost code. — Ulrich Eckhardt, Dec 26 '14 at 10:08
You probably mean `break-to`, `continue` stays at the same nesting level. — , Dec 26 '14 at 10:21

Jasen · Answer 1 · 2014-12-26T10:28:50.487

1

CONTINUE_TO_LOOP3 simple:continue

CONTINUE_TO_LOOP2 easy: break

CONTINUE_TO_LOOP1 this is the interesting one:

cant do that in a single step without using the four letter word goto
or placing a try-catch around loop2 and using a raise to get out.
or assuming there are no code between the end of loop1 and the end of loop2: moo = false ; break ;

edited Dec 26 '14 at 10:28

answered Dec 26 '14 at 10:12

Jasen

11,837
2
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1

http://xkcd.com/292/ – Dec 26 '14 at 10:14
indeed, exceptions are another way. – Jasen Dec 26 '14 at 10:23

score 1 · Accepted Answer · answered Dec 26 '14 at 10:16

Probably you can do this work around.

while (foo==true) // loop1
{

   do
   {
      for(int i=0; i<someNumber ; i++) // loop3
      {

         if( soo==1)
         {
              break;//<CONTINUE_TO_LOOP1>
         }
         else if( soo==2 )
         {
             break;//<CONTINUE_TO_LOOP2>
         }
         else if( soo==3 )
         {
            continue;//<CONTINUE_TO_LOOP3>
         }
      }
      if( soo==1)
      {
         break;//<CONTINUE_TO_LOOP1>
      }
      else if( soo==2 )
      {
          continue;//<CONTINUE_TO_LOOP2>
      }
   } while (moo==true) //loop2    
   if( soo==1)
   {
       continue;//<CONTINUE_TO_LOOP1>
   } 
}

May i know the reason it is down voted? This solution will surely work and i already mentioned its work around. — Sridhar DD, Dec 26 '14 at 10:29

score 1 · Answer 3 · answered Dec 26 '14 at 10:23

With some restructuration, and without goto:

bool loop3()
{
    for (int i=0; i < someNumber ; i++) {
        if(soo == 1) {
            return false;
        } else if(soo == 2) {
            return true;
        } else if(soo == 3) {
            continue;
        }
    }
    return true;
}

And the loops become:

while (foo == true) // loop1
{
   do
   {
       if (loop3() == false) {
           break;
       }
   } while (moo == true) //loop2    
}

score 1 · Answer 4 · answered Dec 26 '14 at 10:27

1

I advocate unconditional branches to expressive labels. Other solutions will cost extra conditional branches and possibly state variables, will be less flexible, and can be much less readable.

answered Dec 26 '14 at 10:27

I also advocate ""Go To Statement Considered Harmful" Considered Harmful". – Dec 26 '14 at 11:49

C++: How to decide the loop to continue to?

4 Answers4