How can I break out of two nested loops in Objective-C?

Question

I have two loops nested as follows:

for(...) { for(...) { } } 

I know there is a break statement. But am I embarrassed if he breaks both loops or just the one in which she was called? I need to break both as soon as I see that it makes no sense to repeat more than once.

Answer 1

break breaks out of one loop, but you can add a check for the outer loop, which breaks when the inner break.

 bool dobreak = false; for ( ..; !dobreak && ..; .. ) { for ( ... ) { if (...) { dobreak = true; break; } } } 

Answer 2

If using goto simplifies the code, then that would be appropriate.

 for (;;) { for (;;) { break; /* breaks inner loop */ } for (;;) { goto outer; /* breaks outer loop */ } } outer:; 

Answer 3

The break statement takes you out of the innermost loop. If you do not need additional overhead in the code, memory, and performance of the allocated state variable, I recommend reorganizing the code into a function or your own method and using return to exit all cycles:

 void do_lots_of_work(void) { int i, j; for(i=0; i<10 ; i++) { for(j=0;j< 10; j++) { .. .. if(disaster_struck()) return; /* Gets us out of the loops, and the function too. */ } } } 

Answer 4

Besides the already mentioned flag variable or goto, you can throw an Objective-C exception:

 @try { for() { for() { @throw ... } } } @catch{ ... } 

Answer 5

Others mentioned how you can set a flag or use goto , but I would recommend refactoring your code so that the inner loop is turned into a separate method. This method can then return some flag to indicate that the outer loop should break . If you name your methods accordingly, it will be more readable.

 for (int i = 0; i < 10; i++) { if (timeToStop(i)) break; } -(bool) timeToStop: (int) i { for (int j = 0; j < 10; j++) { if (somethingBadHappens) return true; } return false; } 

Pseudocode, not tested, but you understand the idea.

Answer 6

The break statement will exit the loop in the region that is the parent loop. If you want to exit the second loop, you can also use a boolean variable that is in the scope of both loops

 bool isTerminated = false; for (...) { if (!isTerminated) { for(...) { ... isTerminated = true; break; } } else { break; } } 

Answer 7

Probably the easiest way is to use the flag variable

 for(i=0; i<10 && (done==false); i++) for(j=0;j< 10; j++){ .. .. if(...){done=true; break;} } 

Answer 8

Change the counter of the upper contour before breaking

 for(i=0; i<10 ; i++) for(j=0;j< 10; j++){ .. .. i = 10; break; } 

Answer 9

Another solution is the factor of the second cycle in the function:

 int i; for(i=0; i<10 ; i++){ if !innerLoop(i) { break; } } bool innerLoop(int i) int j; for(j=0;j< 10; j++){ doSomthing(i,j); if(endcondtion){ return false; } } } 

Answer 10

If a break is performed from a set of nested loops, only the innermost loop in which the break is executed ends. (Same as standard C)

Answer 11

The break statement breaks out of the innermost loop. An additional test and a break statement are required to exit the outer loop.

Answer 12

In the same way as the latter, usually these are:

 for(i=0;i<a;i++){ for(j=0;j<a;j++){ if(Something_goes_wrong){ i=a; break; } } } 

Answer 13

Just for a laugh, how about changing this true / false check in the method and using the return :

 - (bool) checkTrueFalse: parameters{ for ( ...) { for ( ... ) { if (...) { return true; } } } return false; }