How to break out of nested loops

Question

If I use a break statement  it will only break inner loop and I need to use some flag to break the outer loop  But if there are many nested loops  the code will not look good   Is there any other way to break all of the loops   Please don t use goto stmt    for int i   0  i  lt  1000  i         for int j   0  j  lt  1000  j             if condition                   both of the loops need to break and control will go to stmt2                   stmt2

User · Accepted Answer

Use   if  condition        i   j   1000      break

User · Answer

for int i   0  i  lt  1000  i         for int j   0  j  lt  1000  i             if condition                goto end           end

User · Answer

int i   0  j  0   for i i lt  1000  i             for j  j lt  1000  j             if condition               i   j   1001              break                      Will break both the loops

User · Answer

I think goto will solve the problem for int i   0  i  lt  1000  i          for int j   0  j  lt  1000  j              if  condition                goto end                     end  stmt2

User · Answer

I note that the question is simply   quot Is there any other way to break all of the loops  quot  I don t see any qualification but that it not be goto  in particular the OP didn t ask for a good way  So  how about we longjmp out of the inner loop   -   include  lt stdio h gt   include  lt setjmp h gt   int main int argc  char  argv        int counter   0    jmp buf look ma no goto    if   setjmp look ma no goto         for  int i   0  i  lt  1000  i            for  int j   0  j  lt  1000  j              if  i    500  amp  amp  j    500              longjmp look ma no goto  1                     counter                        printf  quot counter  d n quot   counter      The setjmp function returns twice  The first time  it returns 0 and the program executes the nested for loops  Then when the both i and j are 500  it executes longjmp  which causes setjmp to return again with the value 1  skipping over the loop  Not only will longjmp get you out of nested loops  it works with nested functions too

User · Answer

i   0   do     for  int j   0  j  lt  1000  j       by the way  your code uses i   here           if  condition                break                  i     while   i  lt  1000   amp  amp   condition

User · Answer

A different approach is to refactor the code from two for loops into a for loop and one manual loop   That way the break in the manual loop applies to the outer loop   I used this once in a Gauss-Jordan Elimination which required three nested loops to process  for  int i   0  i  lt  1000  i          int j   0   MANUAL LOOP        if  j  lt  1000               if  condition                      break                   j           goto MANUAL LOOP

User · Answer

No  don t spoil the fun with a break  This is the last remaining valid use of goto      If not this then you could use flags to break out of deep nested loops    Another approach to breaking out of a nested loop is to factor out both loops into a separate function  and return from that function when you want to exit    Summarized - to break out of nested loops    use goto use flags factor out loops into separate function calls   Couldn t resist including xkcd here       source  Goto s are considered harmful but as many people in the comments suggest it need not be  If used judiciously it can be a great tool  Anything used in moderation is fun

User · Answer

If you need the values of i and j  this should work but with less performance than others  for i i lt  1000  i             for j  j lt  1000  j             if condition              break            if condition    the same condition         break

User · Answer

Use this wise advice from LLVM team    Turn Predicate Loops into Predicate Functions   See    http   llvm org docs CodingStandards html turn-predicate-loops-into-predicate-functions

User · Answer

for int i   0  i  lt  1000  i          for int j   0  j  lt  1000  i             if condition              func para1  para2                return                    func para1  para2           stmt2

User · Answer

One way is to put all the nested loops into a function and return from the inner most loop incase of a need to break out of all loops   function            for int i 0  i lt 1000  i           for int j 0  j lt 1000 j               if  condition          return

User · Answer

bool stop   false  for  int i   0   i  lt  1000   amp  amp   stop  i          for  int j   0   j  lt  1000   amp  amp   stop  j                  if  condition              stop   true

User · Answer

Caution  This answer shows a truly obscure construction   If you are using GCC  check out this library  Like in PHP  break can accept the number of nested loops you want to exit  You can write something like this   for int i   0  i  lt  1000  i         for int j   0  j  lt  1000  j             if condition                   break two nested enclosing loops             break 2

User · Answer

You ll need a boolean variable  if you want it readable   bool broke   false  for int i   0  i  lt  1000  i        for int j   0  j  lt  1000  i          if  condition          broke   true        break              if  broke      break      If you want it less readable you can join the boolean evaluation   bool broke   false  for int i   0  i  lt  1000  amp  amp   broke  i        for int j   0  j  lt  1000  i          if  condition          broke   true        break                As an ultimate way you can invalidate the initial loop   for int i   0  i  lt  size  i        for int j   0  j  lt  1000  i          if  condition          i   size        break

[c] How to break out of nested loops?

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