OpenEuphoria

Re: Exiting multiple loop constructs

• Posted by Kat <KAT12 at coo?ahs.?et> May 14, 2008
• 1214 views

Jeremy Cowgar wrote:
> 
> We've talked about labeled loops and a bit about existing loop constructs,
> exiting
> loops, etc... but I do not think we came to any conclusive decision. Here is
> a summary of different methods of exiting multiple loops:
> 
> }}}
<eucode>
> integer in_top
> in_top = 1
> 
> while in_top do
>     for i = 1 to 10 do
>         if i = 3 then
>             in_top = 0
>             exit
>         end if
>     end for
> end while
> </eucode>
{{{

> 
> This will work fine unless you have processing *under* the nested loop, then
> you must provide an extra condition check (which is in a loop and is executed
> each iteration):
> 
> }}}
<eucode>
> integer in_top
> in_top = 1
> 
> while in_top do
>     for i = 1 to 10 do
>         if i = 3 then
>             in_top = 0
>             exit
>         end if
>     end for
>     if in_top = 0 then
>         exit
>     end if
>     -- do more processing here
> end while
> </eucode>
{{{

> 
> NOTE: The above two methods compound in complexity with each nested loop you
> add. However, in real life, I'm not sure if I have ever programmed a loop that
> is 3 deep.
> 
> This method uses optional numeric methods to exit and continue keywords:
> 
> }}}
<eucode>
> while 1 do
>     for i = 1 to 10 do
>         if i = 3 then exit 2 -- end if
>     end for
> end while
> </eucode>
{{{

> 
> Notice "exit 2". That means exit 2 loops.
> 
> The final method is labeled loops, in which I will make a slightly more
> advanced
> example.
> 
> }}}
<eucode>
> while 1 label top do
>     for i = 1 to 10 label mid do
>         for j = 1 to 10 label bottom do
>             -- exit current loop "to" the top loop
>             if j = 2 then exit top end if
> 
>             -- exit all loops (in this function) 
>             if j = 5 then exit all end if
>         end for
>     end for
> end while
> </eucode>
{{{

> 
> 
> So. Is one clearer than another? I do not know. Should any syntax change to
> support exiting multiple loops? I am not sure, the benefit is you can remove
> multiple checks making code easier to write and better performing.
> 
> So, what do you think? Are there other ways that I missed? What should be
> done?

I prefer :

while 1 do -- label top
     for i = 1 to 10 do -- label mid
         for j = 1 to 10 do -- label bottom
             -- exit current loop "to" the top loop
             if j = 2 then exit top end if
 
             -- exit all loops (in this function) 
             if j = 5 then exit all end if
         end for
     end for
 end while
 

 
or 

while 1 do
     for i = 1 to 10 do
         for j = 1 to 10 do
             -- exit current loop "to" the top loop
             if j = 2 then goto whereiwanto end if
 
             -- exit all loops (in this function) 
             if j = 5 then goto whereiwantonow end if
         end for
     end for
 end while
 

 

Kat