For Next Loops

[BackupUser]

Restored from previous forum. Originally posted by blueb.

How do you exit early from a For:Next loop?

--blueb

[BackupUser]

Restored from previous forum. Originally posted by blueb.

I've done it with a Goto Label:
e.g.

Code: Select all

Procedure.s PackDir(SourceDir$)
a$ = SourceDir$
For x  = Len(a$) To 1 Step - 1
         cur$=Mid( a$, x, 1)
         If cur$ = "\":
         ; Get out now!!!!
         Goto GetOut
         EndIf
         ans$ = cur$ + ans$
Next
GetOut:     
 ProcedureReturn ans$ 
EndProcedure

;Main
 ans$ = PackDir("c:\Job\BobJob\HarryGuy\Yesterday\BigJob")
 MessageRequester("", ans$,0)

Is this considered "healthy"?
--blueb

[BackupUser]

Restored from previous forum. Originally posted by Berikco.

if you want to exit the procedure, this works to, no need for goto.

Code: Select all

Procedure.s PackDir(SourceDir$)a$ = SourceDir$
For x  = Len(a$) To 1 Step - 1
         cur$=Mid( a$, x, 1)
         If cur$ = "\":
         ; Get out now!!!!
         ;Goto GetOut
         ProcedureReturn ans$         
        EndIf
         ans$ = cur$ + ans$
Next
GetOut:     
 ProcedureReturn "" 
EndProcedure

;Main
ans$ = PackDir("c:\Job\BobJob\HarryGuy\Yesterday\BigJob")
MessageRequester("", ans$,0)



Regards,

Berikco

http://www.benny.zeb.be

[BackupUser]

Restored from previous forum. Originally posted by blueb.

Thanks Berikco,

I wasn't sure that I could have 2 ProcedureReturns in the
same procedure. It works, so that's good.

I didn't like 'Goto' inside a For:Next loop. It
doesn't seem right. {grin}

One way to solve all of these little problems would be to
have a universal "Exit Now" function, like FakeReturn

Maybe Fred can have the FakeReturn verb used for all
loops such as: For:Next, While:Wend, Repeat:Until, etc.
It would return the program to the line following the loop.

thanks again,
--blueb

[BackupUser]

Restored from previous forum. Originally posted by Jose.

How about having a Break for the For Loop exit as is in other languages.

I think that using a GOTO is bad practice as it makes code unreadable, if you must break out of a FOR/NEXT why not use a Repeat/until with a counter, then just set the counter to the exit value;

nCount = 0
Repeat
If nCount > 5 ; some condition
nCount = 999 ; or some other value
EndIf
nCount = nCount + 1
Until nCount >= 10

Just my thoughts

[BackupUser]

Restored from previous forum. Originally posted by blueb.

Code: Select all

For x  = Len(a$) To 1 Step - 1
         cur$=Mid( a$, x, 1)
         If cur$ = "\":
         ; Get out now!!!!
         Goto GetOut
         EndIf
         ans$ = cur$ + ans$
Next

Jose,
For:Next is the only looping device that allows
a negative STEP. (a least according to the help file)

I don't believe Repeat:Until will do what I needed.

--blueb

[BackupUser]

Restored from previous forum. Originally posted by tinman.

Originally posted by blueb
For:Next is the only looping device that allows
a negative STEP. (a least according to the help file)

I don't believe Repeat:Until will do what I needed.

Loops all work the same way - they loop while or until a condition is met. Therefore all loops are interchangable, although some are more appropriate depending on what type of exit checks you must perform and when the loop must be executed (e.g. always executed at least once - Repeat...Until, or conditionally executed the first time - While...Wend).

Code: Select all

For i=50 To 1 Step -1
; exit early
    i = 1
Next

; Repeat might not be the best choice here since you are not 
; always guaranteed to have 1 character in the string and therefore
; the first execution of this loop may be in error
i = 50
Repeat
; exit early
    i = 1

; Loop condition
    i = i - 1
Until i = 1


i = 50
While i>=1
; exit early
    i = 1

; Loop condition
    i = i - 1
Wend

--
It's not minimalist - I'm increasing efficiency by reducing input effort.
(Win98first ed. + SP1, PB3.30)

[BackupUser]

Restored from previous forum. Originally posted by Jose.

Tinman, that's an even easier and better suggestion, just force the loop to terminate by setting the loop variable to the maximum or minimum +1 value, thereby terminating the loop.

; exit early
i = 1

Cleaner code too

[BackupUser]

Restored from previous forum. Originally posted by Justin.

I agree with Jose, the break and continue statements of most languages are for that, i don't understand why Fred hasn't included them.

[BackupUser]

Restored from previous forum. Originally posted by MrVainSCL.

Hi @ all
I thought a litte moment when i saw blueb first code-snip and then i become an idea (havent tested yet if it work or not... but it should work i hope when i dont make a mistake in this hurry...

Code: Select all

Procedure.s PackDir(SourceDir$)
    a$  = SourceDir$
    tmp = Len(a$)
    ;
    For x = tmp To 1 Step - 1
      If break = 0                    ; Loop only as long as break=0
         cur$ = Mid( a$, x, 1)
         ;
         ;-------- Get out now!!!! --------
         ;
         If cur$ = "\":               ; If you want to quit, just
            break = 1                 ; set break=1
            x = 0                     ; We set the ForNextLoop2EndVal
         Else
            ans$ = cur$ + ans$ 
         EndIf
         ;
      EndIf     
    Next
    ;
    ProcedureReturn ans$ 
EndProcedure

ans$ = PackDir("c:\Job\BobJob\HarryGuy\Yesterday\BigJob")
MessageRequester("", ans$,0)

I am to tired to have a clean head and think atm n8


PIII450, 256MB Ram, 80GB HD + 6,4 GB, RivaTNT, DirectX8.1, SB AWE64, Win2000 + all Updates...

greetz
MrVainSCL! aka Thorsten

[BackupUser]

Restored from previous forum. Originally posted by PB.

> How do you exit early from a For:Next loop?

If would be great if Fred adds Break/Continue commands, but until then
you just set the tested condition to the ending "Next" value. So, to
exit from For a=1 to 10, you would use a=10 where you wanted to break.

Code: Select all

; User enters text up to 999 times or until "end" is entered.
OpenConsole()
For a=1 To 999
  Print("Enter text: ")
  a$=Input() : PrintN("")
  If a$="end" : a=999 : EndIf
Next
PrintN("")
PrintN("You broke out of the For/Next loop!")
Input()

PB - Registered PureBasic Coder

[BackupUser]

Restored from previous forum. Originally posted by MrVainSCL.

Hi PB
Its exactly what i do in my example! I think a good coder dont need any Goto nor FakeReturn! )

PIII450, 256MB Ram, 80GB HD + 6,4 GB, RivaTNT, DirectX8.1, SB AWE64, Win2000 + all Updates...

greetz
MrVainSCL! aka Thorsten

[BackupUser]

Restored from previous forum. Originally posted by PB.

> Its exactly what i do in my example!

Hehehe, sorry -- to be honest I didn't read your example.

> I think a good coder dont need any Goto nor FakeReturn! )

It's not considered a good programming practice these days to use
Goto/FakeReturn to exit a loop. The functionality is there for
compatibility reasons, but is best avoided in the first place.


PB - Registered PureBasic Coder

[BackupUser]

Restored from previous forum. Originally posted by MrVainSCL.

@ PB

PIII450, 256MB Ram, 80GB HD + 6,4 GB, RivaTNT, DirectX8.1, SB AWE64, Win2000 + all Updates...

greetz
MrVainSCL! aka Thorsten

[BackupUser]

Restored from previous forum. Originally posted by Justin.

If the idea is this:

For a=1 To 999
messagerequester("",str(a),0)
if a=5 : a=999 : endif ;trying to break
messagerequester("","loop complete",0)
Next

messagerequester("","loop exit",0)

That is not a break, 'loop complete' is executed after forcing a=999, the loop is always finished, a break transfers control inmediately to the statement following the next, endselect or whatever. Everything between the break and the next is not executed, the only way is using a goto.

Continue transfers control to the beginning of the loop, in a for/next the index is incremented, in a select/endselect transfers control to the next case.

The break is extensively used in the windows message loop, look at any c code.