I am preparing some code:
for(int a = 1; a <= 100; a++) //loop a (main loop)
{
for(int b = 1000; b <= 2000; b++) //loop b
{
if(b == 1555)
break;
}
for(int c = 2001; c <= 3000; c++) //loop c
{
.
.
.
}
}
I want to break the main loop (loop variable int a) by using a break; statement in the b loop (loop variable int b).
How can I do it?
Use a goto.
for(int a = 1; a <= 100; a++) //loop a (main loop)
{
for(int b = 1000; b <= 2000; b++) //loop b
{
if(b == 1555)
goto loopDone;
}
for(int c = 2001; c <= 3000; c++) //loop c
{
.
.
.
}
}
loopDone:
for(int a = 1; a <= 100; a++) //loop a (main loop)
{
for(int b = 1000; b <= 2000; b++) //loop b
{
if(b == 1555)
goto end;
}
for(int c = 2001; c <= 3000; c++) //loop c
{
.
.
.
}
}
end:
The only way to head out of two such loops at a time is a goto or a throw or a return, and throw and return may not be appropriate (particularly throw, if the condition isn't exceptional). Alternately, you could set some sort of condition (bool breakout;), and keep breaking if it's true.
Use this kind of pattern
for(int a = 1; a <= 100; a++)
{
int breakMain = 0;
for(int b = 1000; b <= 2000; b++)
{
if(b == 1555)
{
breakMain = 1;
break;
}
}
if(breakMain)
break;
for(int c = 2001; c <= 3000; c++)
{
.
.
.
}
}
By using a condition variable:
for(int a = 1; a <= 100; a++) //loop a (main loop)
{
bool cond = false;
for(int b = 1000; b <= 2000; b++) //loop b
{
if(b == 1555){
cond = true;
break;
}
}
if (cond) break;
.
.
.
}
Alternatively, you could place all of this code inside a function, and just return from that function instead of using break. Perhaps this - or a more involved refactoring of your code - would lend itself to a cleaner solution.
Use a goto:
for(int a = 1; a <= 100; a++) //loop a (main loop)
{
for(int b = 1000; b <= 2000; b++) //loop b
{
if(b == 1555)
goto done;
}
for(int c = 2001; c <= 3000; c++) //loop c
{
.
.
.
}
}
done:
set a sentinel value tested by each loop:
bool sentinel = true ;
for(int a = 1; a <= 100 && sentinel ; a++) //loop a (main loop)
{
for(int b = 1000; b <= 2000 && sentinel; b++) //loop b
{
if(b == 1555)
sentinel = false;
}
for(int c = 2001; c <= 3000 && sentinel; c++) //loop c
{
.
.
.
}
}
If it is appropriate, you could make a function who's contents are the a loop, and use return.
public void bigLoop()
{
for(int a = 1; a <= 100; a++)
{
for(int b = 1000; b <= 2000; b++)
{
if(b == 1555)
return;
}
for(int c = 2001; c <= 3000; c++)
{
.
.
.
}
}
}//bigLoop
One simple strategy is to put the loop in a separate function and do a return at the selected point:
void func()
{
for(int a = 1; a <= 100; a++) //loop a (main loop)
{
for(int b = 1000; b <= 2000; b++) //loop b
{
if(b == 1555)
return;
}
for(int c = 2001; c <= 3000; c++) //loop c
{
.
.
.
}
}
}
Any kind of result may also be returned with a return value, or with a reference parameter for the function.
Either do one of four things: use goto, use throw, use a flag, or refactor.
Many will disagree with using goto, but sometimes it's a clean solution. (Most times, it isn't, but it exists for a reason.) However, I find the use of goto warrants a refactor.
The second solution is to throw some special exception and then catch it just outside the main loop. This is an abuse of the exception system and basically a worse goto; use a goto instead of this.
The third solution would be to use a flag of some sort. This is basically a "safer" goto, but some might argue it's a bit uglier. (Especially with multiple-levels. Though in such a case your concern is how ugly your code is.)
The solution I would recommend is refactor. Whatever you're doing, it's too much. You should move the inner loops into a function, and call that function. Returning to the main loop is simply a return from that function. (In other words "My work is done.")
The ideal way would be to re-factor your code so that you no longer need such a complicated nested-loop structure. Depending on what the rest of your code looks like, your b and c loops may be candidates for becoming individual functions, if not the entire a loop.
Since it looks like loops b and c iterate over adjacent ranges, why not combine them and reduce your loop nesting a bit?
for (int a = 1; a <= 100; a++) //loop a (main loop)
{
int count = 1000;
while (count <= 3000) // combined loops 'b' and 'c'
{
if (count <= 2000)
{
// Old loop 'b' code
if (b == 1555)
goto fullbreak;
}
else
{
// Old loop 'c' code
...
}
count++;
}
}
fullbreak:
You can also use a condition variable instead of the goto. If you want to break out of the old b loop but still process the old c loop, simply set count = 2001 inside the old b loop code.
Ideally, you would at least be able to re-factor this to something more like
for (int a = 1; a <= 100; a++) //loop a (main loop)
{
if (process_inner_loop(pass, required, args))
break;
}
where the function process_inner_loop wraps up your original two loops and returns non-zero if you want to break out of the enclosing loop. Now, instead of using goto or condition variables, you can simply return 1;.
\ (◕ ◡ ◕) /
[]() {
for(int a = 1; a <= 100; a++) //loop a (main loop)
{
for(int b = 1000; b <= 2000; b++) //loop b
{
if(b == 1555)
return;
}
for(int c = 2001; c <= 3000; c++) //loop c
{
.
.
.
}
}
}();