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Re: Loop exit

kalberts31-Jul-14 22:58

kalberts

31-Jul-14 22:58

But does it provide two ways out? I.e. alternate code blocks executed one but not the other, depending on how you exited the loop?

Re: Loop exit

crazedDotNetDev1-Aug-14 10:34

crazedDotNetDev

1-Aug-14 10:34

It depended on the specific language’s implementation. The general rule was it exits from the innermost loop. I seem to remember VB (pre .NET) was able to break from nested loops…

do while true
  for i = 1 to 10
    if i > 5 then
      exit do
    end if
  next
loop

I also got something rattling around in my skull about exiting from named loops, but I don’t believe that was a BASIC language. Google/Bing isn’t being helpful at the moment. Frown | :(

- great coders make code look easy

- When humans are doing things computers could be doing instead, the computers get together late at night and laugh at us. - ¿Neal Ford?

Re: Loop exit

Member 460889831-Jul-14 5:58

Member 4608898

31-Jul-14 5:58

But if you had

for (...) {
for (...) {
I want to exitfor from the outer loop from a condition in the inner loop
}
}

How would you do it? goto was invented for a reason and this is it!!! Big Grin | :-D

Re: Loop exit

kalberts31-Jul-14 22:57

kalberts

31-Jul-14 22:57

CHILL has a very nice solution to this: Every block, whether a procedure, loop, switch or even a linear sequence of statements enclosed with BEGIN and END, could be prefixed with a label. In CHILL, a label does not identify a point in the program, but a block, and consequently label scopes could be nested. So to leave the outer loop, you would write

SQL

OuterLoop: 
DO FOR (...) 

   InnerLoop: 
   DO FOR (...) 
      ...
      IF <done processing this element> THEN EXIT InnerLoop; FI;
      ...
      IF <some fatal condition> THEN EXIT OuterLoop; FI
      ...
   OD

OD

(Here I illustrate both leaving the inner loop and the outer loop.) However, CHILL doesn't provide what I asked for in my original post: If the post-loop processing depends on whether you completed the loop or left prematurely by EXIT, you must set some variable to a magic value and test it after the loop, and the post-loop processing would syntactically (e.g. with respect to variable scope) be outside the loop.

While we are at CHILL: Another nifty syntactic sugar cube is the keyword EVER:

C++

DO FOR EVER
   ...
OD

The semantics of EVER is quite obvious. I like this so much that whenever I need to program an inner loop in C, I set up a

C++

#define ever (;;)

to be able to code it as "for ever {...}" in C.

Sure, any well seasoned C programmer would prefer "while (1) {...}", but even though I have been writing more lines of C code than in any other language the last thirty years, I still read it as "while one what???"

Re: Loop exit

dg6yhw1131-Jul-14 7:25

dg6yhw11

31-Jul-14 7:25

BASIC provides several exit statements such as

EXIT LOOP
EXIT FOR

You can also set the condition in the call to the loop

WHILE Not [answer you want is found] ... WEND will exit when the condition is met (of course you have to add another exit test to avoid infinite loops Smile | :)

There are a bunch of similar constructs.

To use this with some OOP type language just write a little function in BASIC (Visual Studio, PowerBasic), compile to a DLL and call it from the object you need to use.

Visual Studio would probably let you do it all in the same project but then you wouldn't have the DLL to reuse.

Re: Loop exit

Frank Malcolm31-Jul-14 15:40

Frank Malcolm

31-Jul-14 15:40

Delphi's version of Pascal has Break (quit the loop) and Continue (begin the next iteration).

Re: Loop exit

kalberts31-Jul-14 22:19

kalberts

31-Jul-14 22:19

That is like break and continue in C, isn't it?

Does it provide two alternatative ways out of a loop: One alternative is executed if the break was performed,the other if break was not performed? If it does, some more syntax must be defined.

Re: Loop exit

Frank Malcolm1-Aug-14 13:57

Frank Malcolm

1-Aug-14 13:57

I don't know C well enough to comment.

And yes, if you need to know whether you exited the loop because of the break or the for/while/repeat condition, you have to code it separately.

Usually there's some "natural" way to easily determine that, but obviously not always.

Doing an interview today

glennPattonWork329-Jul-14 22:49

glennPattonWork3

29-Jul-14 22:49

Hi All,
The first interview (for some time). Not really sure about it, they haven't really told me or the agent what they will ask (please no Labview)...
GLENN (Also my first post from my S3)

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