Breaking out of a nested loop

Question

If I have a for loop which is nested within another  how can I efficiently come out of both loops  inner and outer  in the quickest possible way   I don t want to have to use a boolean and then have to say go to another method  but rather just to execute the first line of code after the outer loop   What is a quick and nice way of going about this   I was thinking that exceptions aren t cheap should only be thrown in a truly exceptional condition etc  Hence I don t think this solution would be good from a performance perspective   I don t feel it it is right to take advantage of the newer features in  NET  anon methods  to do something which is pretty fundamental

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That s how I did it  Still a workaround    x000D   x000D  foreach  var substring in substrings    x000D      To be used to break from 1st loop  x000D    int breaker 1  x000D    foreach  char c in substring    x000D      if  char IsLetter c     x000D        Console WriteLine line IndexOf c    x000D          setting condition to break from 1st loop  x000D        breaker 9  x000D        break  x000D        x000D      x000D    if  breaker  9    x000D      break  x000D      x000D    x000D   x000D   x000D

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Did you even look at the break keyword  O o  This is just pseudo-code  but you should be able to see what I mean    lt  php for            while                foreach                    break 3                      If you think about break being a function like break    then it s parameter would be the number of loops to break out of  As we are in the third loop in the code here  we can break out of all three   Manual  http   php net break

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That s how I did it  Still a workaround    x000D   x000D  foreach  var substring in substrings    x000D      To be used to break from 1st loop  x000D    int breaker 1  x000D    foreach  char c in substring    x000D      if  char IsLetter c     x000D        Console WriteLine line IndexOf c    x000D          setting condition to break from 1st loop  x000D        breaker 9  x000D        break  x000D        x000D      x000D    if  breaker  9    x000D      break  x000D      x000D    x000D   x000D   x000D

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Use a suitable guard in the outer loop   Set the guard in the inner loop before you break   bool exitedInner   false   for  int i   0  i  lt  N  amp  amp   exitedInner    i              some outer loop stuff      for  int j   0  j  lt  M    j             if  sometest                exitedInner   true              break                      if   exitedInner               more outer loop stuff           Or better yet   abstract the inner loop into a method and exit the outer loop when it returns false   for  int i   0  i  lt  N    i              some outer loop stuff      if   doInner i  N  M            break                 more outer loop stuff

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The cleanest  shortest  and most reusable way is a self invoked anonymous function   no goto no label no temporary variable no named function  One line shorter than the top answer with anonymous method  new Action      gt        for  int x   0  x  lt  100  x                  for  int y   0  y  lt  100  y                          return     exits self invoked lambda expression                       Console WriteLine  quot Hi quot

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factor into a function method and use early return  or rearrange your loops into a while-clause   goto exceptions whatever are certainly not appropriate here   def do until equal      foreach a      foreach b        if a  b  return

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Loops can be broken using custom conditions in the loop  allowing as to have clean code       static void Main string   args                bool isBreak   false          for  int i   0  ConditionLoop isBreak  i  500   i                          Console WriteLine   External loop iteration  i                 for  int j   0  ConditionLoop isBreak  j  500   j                                  Console WriteLine   Inner loop iteration  j                         This code is only to produce the break                  if  j  gt  3                                        isBreak   true                                                                 Console WriteLine  The code after the inner loop will be executed when breaks                       Console ReadKey               private static bool ConditionLoop bool isBreak  int i  int maxIterations    gt  i  lt  maxIterations  amp  amp   isBreak       With this code we ontain the following output    External loop iteration 0 Inner loop iteration 0 Inner loop iteration 1 Inner loop iteration 2 Inner loop iteration 3 Inner loop iteration 4 The code after the inner loop will be executed when breaks

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The easiest way to end a double loop would be directly ending the first loop  string TestStr    The frog jumped over the hill   char   KillChar     w    l     for int i   0  i  lt  TestStr Length  i          for int E   0  E  lt  KillChar Length  E                  if KillChar E     TestStr i                         i   TestStr Length    Ends First Loop             break    Ends Second Loop

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Since I first saw break in C a couple of decades back  this problem has vexed me   I was hoping some language enhancement would have an extension to break which would work thus   break     our trusty friend  breaks out of current looping construct  break 2     breaks out of the current and it s parent looping construct  break 3     breaks out of 3 looping constructs  break all     totally decimates any looping constructs in force

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I think unless you want to do the  boolean thing  the only solution is actually to throw  Which you obviously shouldn t do

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Is it possible to refactor the nested for loop into a private method  That way you could simply  return  out of the method to exit the loop

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This solution does not apply to C   For people who found this question via other languages  Javascript  Java  and D allows labeled breaks and continues   outer  while fn1         while fn2              if fn3    continue outer       if fn4    break outer

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You asked for a combination of quick  nice  no use of a boolean  no use of goto  and C    You ve ruled out all possible ways of doing what you want   The most quick and least ugly way is to use a goto

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Since I first saw break in C a couple of decades back  this problem has vexed me   I was hoping some language enhancement would have an extension to break which would work thus   break     our trusty friend  breaks out of current looping construct  break 2     breaks out of the current and it s parent looping construct  break 3     breaks out of 3 looping constructs  break all     totally decimates any looping constructs in force

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This solution does not apply to C   For people who found this question via other languages  Javascript  Java  and D allows labeled breaks and continues   outer  while fn1         while fn2              if fn3    continue outer       if fn4    break outer

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C  adaptation of approach often used in C - set value of outer loop s variable outside of loop conditions  i e  for loop using int variable INT MAX -1 is often good choice    for  int i   0  i  lt  100  i          for  int j   0  j  lt  100  j                  if  exit condition                           cause the outer loop to break                 use i   INT MAX - 1  otherwise i      INT MIN  lt  100 and loop will continue              i   int MaxValue - 1              Console WriteLine  Hi                   break the inner loop             break                         if you have code in outer loop it will execute after break from inner loop         As note in code says break will not magically jump to next iteration of the outer loop - so if you have code outside of inner loop this approach requires more checks  Consider other solutions in such case   This approach works with for and while loops but does not work for foreach  In case of foreach you won t have code access to the hidden enumerator so you can t change it  and even if you could IEnumerator doesn t have some  MoveToEnd  method    Acknowledgments to inlined comments  authors  i   INT MAX - 1 suggestion by Meta for foreach comment by ygoe    Proper IntMax by jmbpiano remark about code after inner loop by blizpasta

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The easiest way to end a double loop would be directly ending the first loop  string TestStr    The frog jumped over the hill   char   KillChar     w    l     for int i   0  i  lt  TestStr Length  i          for int E   0  E  lt  KillChar Length  E                  if KillChar E     TestStr i                         i   TestStr Length    Ends First Loop             break    Ends Second Loop

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Well  goto  but that is ugly  and not always possible  You can also place the loops into a method  or an anon-method  and use return to exit back to the main code          goto     for  int i   0  i  lt  100  i                  for  int j   0  j  lt  100  j                          goto Foo     yeuck                  Foo      Console WriteLine  Hi      vs      anon-method Action work   delegate       for  int x   0  x  lt  100  x                  for  int y   0  y  lt  100  y                          return     exits anon-method                    work       execute anon-method Console WriteLine  Hi        Note that in C  7 we should get  local functions   which  syntax tbd etc  means it should work something like      local function  declared   inside   another method  void Work         for  int x   0  x  lt  100  x                  for  int y   0  y  lt  100  y                          return     exits local function                    Work       execute local function Console WriteLine  Hi

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I think unless you want to do the  boolean thing  the only solution is actually to throw  Which you obviously shouldn t do

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factor into a function method and use early return  or rearrange your loops into a while-clause   goto exceptions whatever are certainly not appropriate here   def do until equal      foreach a      foreach b        if a  b  return

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bool breakInnerLoop false         for int i 0 i lt  10 i                        for int J 0 i lt  10 i                              if i lt  j                                        breakInnerLoop true                      break                                            if breakInnerLoop                            continue

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Throw a custom exception which goes out outter loop    It works for for foreach or while or any kind of loop and any language that uses try catch exception block  try       foreach  object o in list             foreach  object another in otherList                          some stuff here          if  condition                         throw new CustomExcpetion                              catch  CustomException          log

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Is it possible to refactor the nested for loop into a private method  That way you could simply  return  out of the method to exit the loop

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Don t quote me on this  but you could use goto as suggested in the MSDN  There are other solutions  as including a flag that is checked in each iteration of both loops  Finally you could use an exception as a really heavyweight solution to your problem   GOTO   for   int i   0  i  lt  10    i        for   int j   0  j  lt  10    j              code       if   break condition   goto End           more code        End      Condition   bool exit   false  for   int i   0  i  lt  10  amp  amp   exit    i        for   int j   0  j  lt  10  amp  amp   exit    j              code       if   break condition              exit   true           break     or continue                  more code          Exception   try       for   int i   0  i  lt  10  amp  amp   exit    i            for   int j   0  j  lt  10  amp  amp   exit    j                  code           if   break condition                  throw new Exception                            more code                catch   Exception e

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Sometimes nice to abstract the code into it s own function and than use an early return - early returns are evil though      public void GetIndexOf Transform transform  out int outX  out int outY        outX   -1      outY   -1       for  int x   0  x  lt  Columns Length  x                  var column   Columns x            for  int y   0  y  lt  column Transforms Length  y                          if column Transforms y     transform                                outX   x                  outY   y                   return

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Is it possible to refactor the nested for loop into a private method  That way you could simply  return  out of the method to exit the loop

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You asked for a combination of quick  nice  no use of a boolean  no use of goto  and C    You ve ruled out all possible ways of doing what you want   The most quick and least ugly way is to use a goto

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I ve seen a lot of examples that use  break  but none that use  continue    It still would require a flag of some sort in the inner loop   while  some condition            outer loop stuff              bool get out   false      for                       inner loop stuff                      get out   true          break             if  get out                 some condition false          continue                more out loop stuff

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Well  goto  but that is ugly  and not always possible  You can also place the loops into a method  or an anon-method  and use return to exit back to the main code          goto     for  int i   0  i  lt  100  i                  for  int j   0  j  lt  100  j                          goto Foo     yeuck                  Foo      Console WriteLine  Hi      vs      anon-method Action work   delegate       for  int x   0  x  lt  100  x                  for  int y   0  y  lt  100  y                          return     exits anon-method                    work       execute anon-method Console WriteLine  Hi        Note that in C  7 we should get  local functions   which  syntax tbd etc  means it should work something like      local function  declared   inside   another method  void Work         for  int x   0  x  lt  100  x                  for  int y   0  y  lt  100  y                          return     exits local function                    Work       execute local function Console WriteLine  Hi

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Use a suitable guard in the outer loop   Set the guard in the inner loop before you break   bool exitedInner   false   for  int i   0  i  lt  N  amp  amp   exitedInner    i              some outer loop stuff      for  int j   0  j  lt  M    j             if  sometest                exitedInner   true              break                      if   exitedInner               more outer loop stuff           Or better yet   abstract the inner loop into a method and exit the outer loop when it returns false   for  int i   0  i  lt  N    i              some outer loop stuff      if   doInner i  N  M            break                 more outer loop stuff

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I ve seen a lot of examples that use  break  but none that use  continue    It still would require a flag of some sort in the inner loop   while  some condition            outer loop stuff              bool get out   false      for                       inner loop stuff                      get out   true          break             if  get out                 some condition false          continue                more out loop stuff

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You asked for a combination of quick  nice  no use of a boolean  no use of goto  and C    You ve ruled out all possible ways of doing what you want   The most quick and least ugly way is to use a goto

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This solution does not apply to C   For people who found this question via other languages  Javascript  Java  and D allows labeled breaks and continues   outer  while fn1         while fn2              if fn3    continue outer       if fn4    break outer

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bool breakInnerLoop false         for int i 0 i lt  10 i                        for int J 0 i lt  10 i                              if i lt  j                                        breakInnerLoop true                      break                                            if breakInnerLoop                            continue

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Well  goto  but that is ugly  and not always possible  You can also place the loops into a method  or an anon-method  and use return to exit back to the main code          goto     for  int i   0  i  lt  100  i                  for  int j   0  j  lt  100  j                          goto Foo     yeuck                  Foo      Console WriteLine  Hi      vs      anon-method Action work   delegate       for  int x   0  x  lt  100  x                  for  int y   0  y  lt  100  y                          return     exits anon-method                    work       execute anon-method Console WriteLine  Hi        Note that in C  7 we should get  local functions   which  syntax tbd etc  means it should work something like      local function  declared   inside   another method  void Work         for  int x   0  x  lt  100  x                  for  int y   0  y  lt  100  y                          return     exits local function                    Work       execute local function Console WriteLine  Hi

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factor into a function method and use early return  or rearrange your loops into a while-clause   goto exceptions whatever are certainly not appropriate here   def do until equal      foreach a      foreach b        if a  b  return

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As i see you accepted the answer in which the person refers you goto statement  where in modern programming and in expert opinion goto is a killer  we called it a killer in programming which have some certain reasons  which i will not discuss it over here at this point  but the solution of your question is very simple  you can use a Boolean flag in this kind of scenario like i will demonstrate it in my example               for    j  lt  10  j                                    solution                 bool breakme   false                  for  int k   1  k  lt  10  k                                           place the condition where you want to stop it                     if                                                  breakme   true                          break                                                           if breakme                      break                     simple and plain

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Use a suitable guard in the outer loop   Set the guard in the inner loop before you break   bool exitedInner   false   for  int i   0  i  lt  N  amp  amp   exitedInner    i              some outer loop stuff      for  int j   0  j  lt  M    j             if  sometest                exitedInner   true              break                      if   exitedInner               more outer loop stuff           Or better yet   abstract the inner loop into a method and exit the outer loop when it returns false   for  int i   0  i  lt  N    i              some outer loop stuff      if   doInner i  N  M            break                 more outer loop stuff

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Since I first saw break in C a couple of decades back  this problem has vexed me   I was hoping some language enhancement would have an extension to break which would work thus   break     our trusty friend  breaks out of current looping construct  break 2     breaks out of the current and it s parent looping construct  break 3     breaks out of 3 looping constructs  break all     totally decimates any looping constructs in force

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C  adaptation of approach often used in C - set value of outer loop s variable outside of loop conditions  i e  for loop using int variable INT MAX -1 is often good choice    for  int i   0  i  lt  100  i          for  int j   0  j  lt  100  j                  if  exit condition                           cause the outer loop to break                 use i   INT MAX - 1  otherwise i      INT MIN  lt  100 and loop will continue              i   int MaxValue - 1              Console WriteLine  Hi                   break the inner loop             break                         if you have code in outer loop it will execute after break from inner loop         As note in code says break will not magically jump to next iteration of the outer loop - so if you have code outside of inner loop this approach requires more checks  Consider other solutions in such case   This approach works with for and while loops but does not work for foreach  In case of foreach you won t have code access to the hidden enumerator so you can t change it  and even if you could IEnumerator doesn t have some  MoveToEnd  method    Acknowledgments to inlined comments  authors  i   INT MAX - 1 suggestion by Meta for foreach comment by ygoe    Proper IntMax by jmbpiano remark about code after inner loop by blizpasta

User · Answer

This solution does not apply to C   For people who found this question via other languages  Javascript  Java  and D allows labeled breaks and continues   outer  while fn1         while fn2              if fn3    continue outer       if fn4    break outer

User · Answer

The cleanest  shortest  and most reusable way is a self invoked anonymous function   no goto no label no temporary variable no named function  One line shorter than the top answer with anonymous method  new Action      gt        for  int x   0  x  lt  100  x                  for  int y   0  y  lt  100  y                          return     exits self invoked lambda expression                       Console WriteLine  quot Hi quot

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Well  goto  but that is ugly  and not always possible  You can also place the loops into a method  or an anon-method  and use return to exit back to the main code          goto     for  int i   0  i  lt  100  i                  for  int j   0  j  lt  100  j                          goto Foo     yeuck                  Foo      Console WriteLine  Hi      vs      anon-method Action work   delegate       for  int x   0  x  lt  100  x                  for  int y   0  y  lt  100  y                          return     exits anon-method                    work       execute anon-method Console WriteLine  Hi        Note that in C  7 we should get  local functions   which  syntax tbd etc  means it should work something like      local function  declared   inside   another method  void Work         for  int x   0  x  lt  100  x                  for  int y   0  y  lt  100  y                          return     exits local function                    Work       execute local function Console WriteLine  Hi

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It seems to me like people dislike a goto statement a lot  so I felt the need to straighten this out a bit    I believe the  emotions  people have about goto eventually boil down to understanding of code and  misconceptions  about possible performance implications  Before answering the question  I will therefore first go into some of the details on how it s compiled   As we all know  C  is compiled to IL  which is then compiled to assembler using an SSA compiler  I ll give a bit of insights into how this all works  and then try to answer the question itself   From C  to IL  First we need a piece of C  code  Let s start simple   foreach  var item in array                    break                 I ll do this step by step to give you a good idea of what happens under the hood   First translation  from foreach to the equivalent for loop  Note  I m using an array here  because I don t want to get into details of IDisposable -- in which case I d also have to use an IEnumerable    for  int i 0  i lt array Length    i        var item   array i                  break                 Second translation  the for and break is translated into an easier equivalent   int i 0  while  i  lt  array Length        var item   array i                  break                   i      And third translation  this is the equivalent of the IL code   we change break and while into a branch       int i 0     for initialization  startLoop      if  i  gt   array Length     for condition               goto exitLoop            var item   array i                  goto exitLoop     break                  i               for post-expression     goto startLoop     While the compiler does these things in a single step  it gives you insight into the process  The IL code that evolves from the C  program is the literal translation of the last C  code  You can see for yourself here  https   dotnetfiddle net QaiLRz  click  view IL    Now  one thing you have observed here is that during the process  the code becomes more complex  The easiest way to observe this is by the fact that we needed more and more code to ackomplish the same thing  You might also argue that foreach  for  while and break are actually short-hands for goto  which is partly true   From IL to Assembler  The  NET JIT compiler is an SSA compiler  I won t go into all the details of SSA form here and how to create an optimizing compiler  it s just too much  but can give a basic understanding about what will happen  For a deeper understanding  it s best to start reading up on optimizing compilers  I do like this book for a brief introduction  http   ssabook gforge inria fr latest book pdf   and LLVM  llvm org    Every optimizing compiler relies on the fact that code is easy and follows predictable patterns  In the case of FOR loops  we use graph theory to analyze branches  and then optimize things like cycli in our branches  e g  branches backwards     However  we now have forward branches to implement our loops  As you might have guessed  this is actually one of the first steps the JIT is going to fix  like this       int i 0     for initialization      if  i  gt   array Length     for condition               goto endOfLoop         startLoop      var item   array i                  goto endOfLoop     break                  i               for post-expression      if  i  gt   array Length     for condition               goto startLoop         endOfLoop               As you can see  we now have a backward branch  which is our little loop  The only thing that s still nasty here is the branch that we ended up with due to our break statement  In some cases  we can move this in the same way  but in others it s there to stay   So why does the compiler do this  Well  if we can unroll the loop  we might be able to vectorize it  We might even be able to proof that there s just constants being added  which means our whole loop could vanish into thin air  To summarize  by making the patterns predictable  by making the branches predictable   we can proof that certain conditions hold in our loop  which means we can do magic during the JIT optimization   However  branches tend to break those nice predictable patterns  which is something optimizers therefore kind-a dislike  Break  continue  goto - they all intend to break these predictable patterns- and are therefore not really  nice    You should also realize at this point that a simple foreach is more predictable then a bunch of goto statements that go all over the place  In terms of  1  readability and  2  from an optimizer perspective  it s both the better solution    Another thing worth mentioning is that it s very relevant for optimizing compilers to assign registers to variables  a process called register allocation   As you might know  there s only a finite number of registers in your CPU and they are by far the fastest pieces of memory in your hardware  Variables used in code that s in the inner-most loop  are more likely to get a register assigned  while variables outside of your loop are less important  because this code is probably hit less    Help  too much complexity    what should I do   The bottom line is that you should always use the language constructs you have at your disposal  which will usually  implictly  build predictable patterns for your compiler  Try to avoid strange branches if possible  specifically  break  continue  goto or a return in the middle of nothing     The good news here is that these predictable patterns are both easy to read  for humans  and easy to spot  for compilers     One of those patterns is called SESE  which stands for Single Entry Single Exit   And now we get to the real question   Imagine that you have something like this      a is a variable   for  int i 0  i lt 100    i       for  int j 0  j lt 100    j                        if  i j  gt  a                     break everything                The easiest way to make this a predictable pattern is to simply eliminate the if completely   int i  j  for  i 0  i lt 100  amp  amp  i j  lt   a    i       for  j 0  j lt 100  amp  amp  i j  lt   a    j                          In other cases you can also split the method into 2 methods      Outer loop in method 1   for  i 0  i lt 100  amp  amp  processInner i     i        private bool processInner int i      int j    for  j 0  j lt 100  amp  amp  i j  lt   a    j                        return i j lt  a      Temporary variables  Good  bad or ugly   You might even decide to return a boolean from within the loop  but I personally prefer the SESE form because that s how the compiler will see it and I think it s cleaner to read    Some people think it s cleaner to use a temporary variable  and propose a solution like this   bool more   true  for  int i 0  i lt 100    i       for  int j 0  j lt 100    j                        if  i j  gt  a    more   false  break       yuck                    if   more    break       yuck                      I personally am opposed to this approach  Look again on how the code is compiled  Now think about what this will do with these nice  predictable patterns  Get the picture    Right  let me spell it out  What will happen is that    The compiler will write out everything as branches   As an optimization step  the compiler will do data flow analysis in an attempt to remove the strange more variable that only happens to be used in control flow   If succesful  the variable more will be eliminated from the program  and only branches remain  These branches will be optimized  so you will get only a single branch out of the inner loop  If unsuccesful  the variable more is definitely used in the inner-most loop  so if the compiler won t optimize it away  it has a high chance to be allocated to a register  which eats up valuable register memory     So  to summarize  the optimizer in your compiler will go into a hell of a lot of trouble to figure out that more is only used for the control flow  and in the best case scenario will translate it to a single branch outside of the outer for loop   In other words  the best case scenario is that it will end up with the equivalent of this   for  int i 0  i lt 100    i       for  int j 0  j lt 100    j                       if  i j  gt  a    goto exitLoop       perhaps add a comment                            exitLoop            My personal opinion on this is quite simple  if this is what we intended all along  let s make the world easier for both the compiler and readability  and write that right away    tl dr   Bottom line    Use a simple condition in your for loop if possible  Stick to the high-level language constructs you have at your disposal as much as possible  If everything fails and you re left with either goto or bool more  prefer the former

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Sometimes nice to abstract the code into it s own function and than use an early return - early returns are evil though      public void GetIndexOf Transform transform  out int outX  out int outY        outX   -1      outY   -1       for  int x   0  x  lt  Columns Length  x                  var column   Columns x            for  int y   0  y  lt  column Transforms Length  y                          if column Transforms y     transform                                outX   x                  outY   y                   return

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Use a suitable guard in the outer loop   Set the guard in the inner loop before you break   bool exitedInner   false   for  int i   0  i  lt  N  amp  amp   exitedInner    i              some outer loop stuff      for  int j   0  j  lt  M    j             if  sometest                exitedInner   true              break                      if   exitedInner               more outer loop stuff           Or better yet   abstract the inner loop into a method and exit the outer loop when it returns false   for  int i   0  i  lt  N    i              some outer loop stuff      if   doInner i  N  M            break                 more outer loop stuff

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It seems to me like people dislike a goto statement a lot  so I felt the need to straighten this out a bit    I believe the  emotions  people have about goto eventually boil down to understanding of code and  misconceptions  about possible performance implications  Before answering the question  I will therefore first go into some of the details on how it s compiled   As we all know  C  is compiled to IL  which is then compiled to assembler using an SSA compiler  I ll give a bit of insights into how this all works  and then try to answer the question itself   From C  to IL  First we need a piece of C  code  Let s start simple   foreach  var item in array                    break                 I ll do this step by step to give you a good idea of what happens under the hood   First translation  from foreach to the equivalent for loop  Note  I m using an array here  because I don t want to get into details of IDisposable -- in which case I d also have to use an IEnumerable    for  int i 0  i lt array Length    i        var item   array i                  break                 Second translation  the for and break is translated into an easier equivalent   int i 0  while  i  lt  array Length        var item   array i                  break                   i      And third translation  this is the equivalent of the IL code   we change break and while into a branch       int i 0     for initialization  startLoop      if  i  gt   array Length     for condition               goto exitLoop            var item   array i                  goto exitLoop     break                  i               for post-expression     goto startLoop     While the compiler does these things in a single step  it gives you insight into the process  The IL code that evolves from the C  program is the literal translation of the last C  code  You can see for yourself here  https   dotnetfiddle net QaiLRz  click  view IL    Now  one thing you have observed here is that during the process  the code becomes more complex  The easiest way to observe this is by the fact that we needed more and more code to ackomplish the same thing  You might also argue that foreach  for  while and break are actually short-hands for goto  which is partly true   From IL to Assembler  The  NET JIT compiler is an SSA compiler  I won t go into all the details of SSA form here and how to create an optimizing compiler  it s just too much  but can give a basic understanding about what will happen  For a deeper understanding  it s best to start reading up on optimizing compilers  I do like this book for a brief introduction  http   ssabook gforge inria fr latest book pdf   and LLVM  llvm org    Every optimizing compiler relies on the fact that code is easy and follows predictable patterns  In the case of FOR loops  we use graph theory to analyze branches  and then optimize things like cycli in our branches  e g  branches backwards     However  we now have forward branches to implement our loops  As you might have guessed  this is actually one of the first steps the JIT is going to fix  like this       int i 0     for initialization      if  i  gt   array Length     for condition               goto endOfLoop         startLoop      var item   array i                  goto endOfLoop     break                  i               for post-expression      if  i  gt   array Length     for condition               goto startLoop         endOfLoop               As you can see  we now have a backward branch  which is our little loop  The only thing that s still nasty here is the branch that we ended up with due to our break statement  In some cases  we can move this in the same way  but in others it s there to stay   So why does the compiler do this  Well  if we can unroll the loop  we might be able to vectorize it  We might even be able to proof that there s just constants being added  which means our whole loop could vanish into thin air  To summarize  by making the patterns predictable  by making the branches predictable   we can proof that certain conditions hold in our loop  which means we can do magic during the JIT optimization   However  branches tend to break those nice predictable patterns  which is something optimizers therefore kind-a dislike  Break  continue  goto - they all intend to break these predictable patterns- and are therefore not really  nice    You should also realize at this point that a simple foreach is more predictable then a bunch of goto statements that go all over the place  In terms of  1  readability and  2  from an optimizer perspective  it s both the better solution    Another thing worth mentioning is that it s very relevant for optimizing compilers to assign registers to variables  a process called register allocation   As you might know  there s only a finite number of registers in your CPU and they are by far the fastest pieces of memory in your hardware  Variables used in code that s in the inner-most loop  are more likely to get a register assigned  while variables outside of your loop are less important  because this code is probably hit less    Help  too much complexity    what should I do   The bottom line is that you should always use the language constructs you have at your disposal  which will usually  implictly  build predictable patterns for your compiler  Try to avoid strange branches if possible  specifically  break  continue  goto or a return in the middle of nothing     The good news here is that these predictable patterns are both easy to read  for humans  and easy to spot  for compilers     One of those patterns is called SESE  which stands for Single Entry Single Exit   And now we get to the real question   Imagine that you have something like this      a is a variable   for  int i 0  i lt 100    i       for  int j 0  j lt 100    j                        if  i j  gt  a                     break everything                The easiest way to make this a predictable pattern is to simply eliminate the if completely   int i  j  for  i 0  i lt 100  amp  amp  i j  lt   a    i       for  j 0  j lt 100  amp  amp  i j  lt   a    j                          In other cases you can also split the method into 2 methods      Outer loop in method 1   for  i 0  i lt 100  amp  amp  processInner i     i        private bool processInner int i      int j    for  j 0  j lt 100  amp  amp  i j  lt   a    j                        return i j lt  a      Temporary variables  Good  bad or ugly   You might even decide to return a boolean from within the loop  but I personally prefer the SESE form because that s how the compiler will see it and I think it s cleaner to read    Some people think it s cleaner to use a temporary variable  and propose a solution like this   bool more   true  for  int i 0  i lt 100    i       for  int j 0  j lt 100    j                        if  i j  gt  a    more   false  break       yuck                    if   more    break       yuck                      I personally am opposed to this approach  Look again on how the code is compiled  Now think about what this will do with these nice  predictable patterns  Get the picture    Right  let me spell it out  What will happen is that    The compiler will write out everything as branches   As an optimization step  the compiler will do data flow analysis in an attempt to remove the strange more variable that only happens to be used in control flow   If succesful  the variable more will be eliminated from the program  and only branches remain  These branches will be optimized  so you will get only a single branch out of the inner loop  If unsuccesful  the variable more is definitely used in the inner-most loop  so if the compiler won t optimize it away  it has a high chance to be allocated to a register  which eats up valuable register memory     So  to summarize  the optimizer in your compiler will go into a hell of a lot of trouble to figure out that more is only used for the control flow  and in the best case scenario will translate it to a single branch outside of the outer for loop   In other words  the best case scenario is that it will end up with the equivalent of this   for  int i 0  i lt 100    i       for  int j 0  j lt 100    j                       if  i j  gt  a    goto exitLoop       perhaps add a comment                            exitLoop            My personal opinion on this is quite simple  if this is what we intended all along  let s make the world easier for both the compiler and readability  and write that right away    tl dr   Bottom line    Use a simple condition in your for loop if possible  Stick to the high-level language constructs you have at your disposal as much as possible  If everything fails and you re left with either goto or bool more  prefer the former

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C  adaptation of approach often used in C - set value of outer loop s variable outside of loop conditions  i e  for loop using int variable INT MAX -1 is often good choice    for  int i   0  i  lt  100  i          for  int j   0  j  lt  100  j                  if  exit condition                           cause the outer loop to break                 use i   INT MAX - 1  otherwise i      INT MIN  lt  100 and loop will continue              i   int MaxValue - 1              Console WriteLine  Hi                   break the inner loop             break                         if you have code in outer loop it will execute after break from inner loop         As note in code says break will not magically jump to next iteration of the outer loop - so if you have code outside of inner loop this approach requires more checks  Consider other solutions in such case   This approach works with for and while loops but does not work for foreach  In case of foreach you won t have code access to the hidden enumerator so you can t change it  and even if you could IEnumerator doesn t have some  MoveToEnd  method    Acknowledgments to inlined comments  authors  i   INT MAX - 1 suggestion by Meta for foreach comment by ygoe    Proper IntMax by jmbpiano remark about code after inner loop by blizpasta

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I remember from my student days that it was said it s mathematically provable that you can do anything in code without a goto  i e  there is no situation where goto is the only answer    So  I never use goto s  just my personal preference  not suggesting that i m right or wrong   Anyways  to break out of nested loops I do something like this   var isDone   false  for  var x in collectionX        for  var y in collectionY            for  var z in collectionZ                if  conditionMet                       some code                 isDone   true                            if  isDone                  break                    if  isDone               break            if  isDone          break          i hope that helps for those who like me are anti-goto  fanboys

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I remember from my student days that it was said it s mathematically provable that you can do anything in code without a goto  i e  there is no situation where goto is the only answer    So  I never use goto s  just my personal preference  not suggesting that i m right or wrong   Anyways  to break out of nested loops I do something like this   var isDone   false  for  var x in collectionX        for  var y in collectionY            for  var z in collectionZ                if  conditionMet                       some code                 isDone   true                            if  isDone                  break                    if  isDone               break            if  isDone          break          i hope that helps for those who like me are anti-goto  fanboys

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As i see you accepted the answer in which the person refers you goto statement  where in modern programming and in expert opinion goto is a killer  we called it a killer in programming which have some certain reasons  which i will not discuss it over here at this point  but the solution of your question is very simple  you can use a Boolean flag in this kind of scenario like i will demonstrate it in my example               for    j  lt  10  j                                    solution                 bool breakme   false                  for  int k   1  k  lt  10  k                                           place the condition where you want to stop it                     if                                                  breakme   true                          break                                                           if breakme                      break                     simple and plain

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factor into a function method and use early return  or rearrange your loops into a while-clause   goto exceptions whatever are certainly not appropriate here   def do until equal      foreach a      foreach b        if a  b  return

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Since I first saw break in C a couple of decades back  this problem has vexed me   I was hoping some language enhancement would have an extension to break which would work thus   break     our trusty friend  breaks out of current looping construct  break 2     breaks out of the current and it s parent looping construct  break 3     breaks out of 3 looping constructs  break all     totally decimates any looping constructs in force

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Did you even look at the break keyword  O o  This is just pseudo-code  but you should be able to see what I mean    lt  php for            while                foreach                    break 3                      If you think about break being a function like break    then it s parameter would be the number of loops to break out of  As we are in the third loop in the code here  we can break out of all three   Manual  http   php net break

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I ve seen a lot of examples that use  break  but none that use  continue    It still would require a flag of some sort in the inner loop   while  some condition            outer loop stuff              bool get out   false      for                       inner loop stuff                      get out   true          break             if  get out                 some condition false          continue                more out loop stuff

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Loops can be broken using custom conditions in the loop  allowing as to have clean code       static void Main string   args                bool isBreak   false          for  int i   0  ConditionLoop isBreak  i  500   i                          Console WriteLine   External loop iteration  i                 for  int j   0  ConditionLoop isBreak  j  500   j                                  Console WriteLine   Inner loop iteration  j                         This code is only to produce the break                  if  j  gt  3                                        isBreak   true                                                                 Console WriteLine  The code after the inner loop will be executed when breaks                       Console ReadKey               private static bool ConditionLoop bool isBreak  int i  int maxIterations    gt  i  lt  maxIterations  amp  amp   isBreak       With this code we ontain the following output    External loop iteration 0 Inner loop iteration 0 Inner loop iteration 1 Inner loop iteration 2 Inner loop iteration 3 Inner loop iteration 4 The code after the inner loop will be executed when breaks

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You asked for a combination of quick  nice  no use of a boolean  no use of goto  and C    You ve ruled out all possible ways of doing what you want   The most quick and least ugly way is to use a goto

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I ve seen a lot of examples that use  break  but none that use  continue    It still would require a flag of some sort in the inner loop   while  some condition            outer loop stuff              bool get out   false      for                       inner loop stuff                      get out   true          break             if  get out                 some condition false          continue                more out loop stuff

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C  adaptation of approach often used in C - set value of outer loop s variable outside of loop conditions  i e  for loop using int variable INT MAX -1 is often good choice    for  int i   0  i  lt  100  i          for  int j   0  j  lt  100  j                  if  exit condition                           cause the outer loop to break                 use i   INT MAX - 1  otherwise i      INT MIN  lt  100 and loop will continue              i   int MaxValue - 1              Console WriteLine  Hi                   break the inner loop             break                         if you have code in outer loop it will execute after break from inner loop         As note in code says break will not magically jump to next iteration of the outer loop - so if you have code outside of inner loop this approach requires more checks  Consider other solutions in such case   This approach works with for and while loops but does not work for foreach  In case of foreach you won t have code access to the hidden enumerator so you can t change it  and even if you could IEnumerator doesn t have some  MoveToEnd  method    Acknowledgments to inlined comments  authors  i   INT MAX - 1 suggestion by Meta for foreach comment by ygoe    Proper IntMax by jmbpiano remark about code after inner loop by blizpasta

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Is it possible to refactor the nested for loop into a private method  That way you could simply  return  out of the method to exit the loop

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I think unless you want to do the  boolean thing  the only solution is actually to throw  Which you obviously shouldn t do

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Don t quote me on this  but you could use goto as suggested in the MSDN  There are other solutions  as including a flag that is checked in each iteration of both loops  Finally you could use an exception as a really heavyweight solution to your problem   GOTO   for   int i   0  i  lt  10    i        for   int j   0  j  lt  10    j              code       if   break condition   goto End           more code        End      Condition   bool exit   false  for   int i   0  i  lt  10  amp  amp   exit    i        for   int j   0  j  lt  10  amp  amp   exit    j              code       if   break condition              exit   true           break     or continue                  more code          Exception   try       for   int i   0  i  lt  10  amp  amp   exit    i            for   int j   0  j  lt  10  amp  amp   exit    j                  code           if   break condition                  throw new Exception                            more code                catch   Exception e

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Throw a custom exception which goes out outter loop    It works for for foreach or while or any kind of loop and any language that uses try catch exception block  try       foreach  object o in list             foreach  object another in otherList                          some stuff here          if  condition                         throw new CustomExcpetion                              catch  CustomException          log

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I think unless you want to do the  boolean thing  the only solution is actually to throw  Which you obviously shouldn t do

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Don t quote me on this  but you could use goto as suggested in the MSDN  There are other solutions  as including a flag that is checked in each iteration of both loops  Finally you could use an exception as a really heavyweight solution to your problem   GOTO   for   int i   0  i  lt  10    i        for   int j   0  j  lt  10    j              code       if   break condition   goto End           more code        End      Condition   bool exit   false  for   int i   0  i  lt  10  amp  amp   exit    i        for   int j   0  j  lt  10  amp  amp   exit    j              code       if   break condition              exit   true           break     or continue                  more code          Exception   try       for   int i   0  i  lt  10  amp  amp   exit    i            for   int j   0  j  lt  10  amp  amp   exit    j                  code           if   break condition                  throw new Exception                            more code                catch   Exception e

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Don t quote me on this  but you could use goto as suggested in the MSDN  There are other solutions  as including a flag that is checked in each iteration of both loops  Finally you could use an exception as a really heavyweight solution to your problem   GOTO   for   int i   0  i  lt  10    i        for   int j   0  j  lt  10    j              code       if   break condition   goto End           more code        End      Condition   bool exit   false  for   int i   0  i  lt  10  amp  amp   exit    i        for   int j   0  j  lt  10  amp  amp   exit    j              code       if   break condition              exit   true           break     or continue                  more code          Exception   try       for   int i   0  i  lt  10  amp  amp   exit    i            for   int j   0  j  lt  10  amp  amp   exit    j                  code           if   break condition                  throw new Exception                            more code                catch   Exception e

[c#] Breaking out of a nested loop

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