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My first C++ problem :(

I have just started using C++ for the first time and I love it!!!

First problem I have encoutered proably a simple one but

for (int a=0; a<10; a++) {
 for (int b=0; b<10; b++) {
  for (int c=0; c<10; c++) {
   if (b == 5) {
    break; beak; break; break;
   }
  }
 }
}


Now the idea is if b is equal to 5 then it breaks out of the if loop, the for loop c, the for loop b, the for loop a.

Am I doing it right?

If not can someoone please correct me?

Thankyou, Regards X

PS: While on the topic what happens if I only wanted to break out of the if loop or if loop + for loop a or if loop + for loop a + for loop b. Thanks Again.

OmniX
Practically a Master Poster
656 posts since Dec 2007
Reputation Points: 31
Solved Threads: 10
 

>Now the idea is if b is equal to 5 then it breaks out of
>the if loop, the for loop c, the for loop b, the for loop a.
Nope. You can write as many breaks as you want, but only the first one will have any effect, and it'll break you out of the inner-most loop (the c loop).

>If not can someoone please correct me?
You have options here, but the best option is not to get into such a situation to begin with. If you need to break out of a nested loop, it's usually best (if you can manage it) to refactor the nested loops into a function and then use the return value to break:

for ( int a = 0; a < 10; a++ ) {
  if ( !some_function() )
    break;
}

...

bool some_function()
{
  for ( int b = 0; b < 10; b++ ) {
    for ( int c = 0; c < 10; c++ ) {
      if ( b == 5 )
        return false;
    }
  }

  return true;
}
Narue
Bad Cop
Administrator
15,460 posts since Sep 2004
Reputation Points: 6,464
Solved Threads: 1,401
 

That would be a good idea use of functions but I am not able to in this problem :(

If i set it to a bool function then return false it will break me out completly, correct?

I require to just break out for loops a, b, c when required what would I do in that case?

Eg.
Break out of for loop a:
Break out of for loop a, b:
Break out of for loop a, b, c:

Thanks, Regards X

OmniX
Practically a Master Poster
656 posts since Dec 2007
Reputation Points: 31
Solved Threads: 10
 

Then use goto

for (int a=0; a<10; a++) {
  for (int b=0; b<10; b++) {
   for (int c=0; c<10; c++) {
     if (b == 5)
          goto endloop;
   }
 }
}
endloop:
invisal
Posting Pro
562 posts since Mar 2005
Reputation Points: 350
Solved Threads: 64
 

Thanks!!!

Very nice, so I can have multiple goto statements also?

a;
b;
c;

goto a;

goto b;

goto c;

Something like that?

OmniX
Practically a Master Poster
656 posts since Dec 2007
Reputation Points: 31
Solved Threads: 10
 

Of course you can have multiple of them. However, try to avoid using it as much as possible since most of the time goto can be replaced with a loop. For some case such as break multiple-level of loops, goto is inevitable.

invisal
Posting Pro
562 posts since Mar 2005
Reputation Points: 350
Solved Threads: 64
 

>For some case such as break multiple-level of loops, goto is inevitable.
I wouldn't say inevitable, but goto can be the cleanest solution if you have deep nesting and can't refactor it. The alternative is to use flags and check them at each level, which is a "pure" structured solution, but it's almost always ugly as sin.

Narue
Bad Cop
Administrator
15,460 posts since Sep 2004
Reputation Points: 6,464
Solved Threads: 1,401
 

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