Exit Select block?

BlitzMax Forums/BlitzMax Programming/Exit Select block?

Steffenk

(Posted 2008) [#1]

Today i've come to need, but didn't find a way to exit out of a select block explicitly. Looks like some Basic dialects use "Exit Select" for this, while C has its "break".
Of course, there's always the workaround of enveloping the Select block with and If block and using Exit, but i'd prefer a cleaner way.

tonyg

(Posted 2008) [#2]

Doesn't 'Exit' work? If not post your code.

MGE	(Posted 2008) [#3]

Are you trying to say Blitzmax will continue checking though all of the Cases?

Global b:Int
Global a:Int=1
Select a
Case 1
 b=1
 a=2
Case 2
 b=2
 a=3
Case 3
 b=3
 a=4
Case 4
 b=4
 a=5
Case 5
 b=5
End Select
Print b

Looks to me once it finds a "case" it doesn't check anymore so it auto exits. :)

Steffenk

(Posted 2008) [#4]

a = 3
b = 2
Select a
Case 3
	Print "before"
	If b = 2 Exit
	Print "after"
End Select

doesn't compile.

Grey Alien

(Posted 2008) [#5]

From the Docs:

Exit causes program flow to exit the enclosing While, Repeat or For loop.

What you need is this:

a = 3
b = 2
Select a
Case 3
	Print "before"
	If b <> 2 then
	   Print "after"
        EndIf
End Select

Or if the code is in a small function you could perhaps say If b=2 then Return which will exit the whole function.

Steffenk

(Posted 2008) [#6]

I knew there were workarounds, but seeing how other languages do have a keyword for this, I'd find it appropriate for BMax to have on too.

GfK	(Posted 2008) [#7]

If you have your Select block in a function, and there's nothing else in the function after the Select block, just stick a 'Return' in.

Grey Alien

(Posted 2008) [#8]

I said that ;-)

Philip7

(Posted 2008) [#9]

Or you could try:

Global b:Int
Global a:Int=1
Select a
Case 1
 b=1
 aTMP=2
 a=999 'Soft Exit-code
Case 2
 b=2
 aTMP=3
 a=999
...
...
Case 999
 a=aTMP
End Select
Print b

But maybe this is not a clean way?

Oh, or this:

Global b:Int
Global a:Int=1
Local aTMP:Int = a
Select aTMP
Case 1
 b=1
 a=2
Case 2
 b=2
 a=3
...
...
End Select
Print b

Looks pretty clean to me.

Brucey

(Posted 2008) [#10]

 a=999 'Soft Exit-code

Select in BlitzMax is *not* like switch in C/C++/Java/etc.
Once you are in a Case, it won't fall through to any others. Once the end of Case is reached, code drops down to the statement after End Select.

Philip7

(Posted 2008) [#11]

Ah, good. Im used to EasyTrieve (Cobol variant), it falls through there :(

TomToad

(Posted 2008) [#12]

Here's an ugly way of doing it. :)

a = 3
b = 2
Select a
Case 3
	Repeat 'Create a loop to exit from
		Print "before"
		If b = 2 Exit
		Print "after"
	Until 1 'Always exit the loop after one time through
End Select

peltazoid

(Posted 2008) [#13]

I don't get why you need to exit out of a case block.

A case block will end when it reaches the next case, default or end select.

i.e

superstrict
local a : int = 2
local b : int

select a
case 1
    ' blah
case 2
   ' only the code here 
   ' upto here will be executed
   ' even having the following line
   a = 1
   b = 2
   ' will not stay in the case structure as it does not loop
   ' 
case 3
    ' blah
end select
' code will resume here
print b

It is not like a loop where you may need to 'exit' out prematurely and I'm sure blitzmax will use short circuit evaluation so only upto a match does it evaluate the testing expression.

So you don't need to exit from a case at all.

Cheers.

TomToad

(Posted 2008) [#14]

I don't get why you need to exit out of a case block.

If you want to exit a Case before the end of it.

Suppose you have a character that can walk left, walk right, climb up a ladder, or slide down a chute. While he is walking, he could be on a platform or a treadmill. Do a select for which type of movement he is doing. If he is walking, then move the character left or right, unless he's on a treadmill, then any movement will cause him to stand still.
psudocode:

Select State
Case WalkingLeft
   If OnTreadmill 'character on treadmill?
      If TreadmillLeft
         CharacterX :- 1 'Move the character faster if same direction as treadmill
      Else
         Exit 'exit from this case with no movement
      End If
   End If
   CharacterX :- 1
Case WalkingRight
   If OnTreadmill 'Character on treadmill?
      If TreadmillRight
         CharacterX :+ 1 'Move the character faster if same direction
      else
         Exit 'exit from this case with no movement
      End If
   End If
   Character :+ 1
Case Climbing
   CharacterY :- 1
Case Sliding
   CharacterY :+ 1
Case Standing
End Select

I know there are other ways to code that without needing an Exit, but sometimes it is just simpler to use.

peltazoid

(Posted 2008) [#15]

I know there are other ways to code that without needing an Exit, but sometimes it is just simpler to use.

Yes, in your example not to have the else statement ;)

CS_TBL

(Posted 2008) [#16]

I dunno about all this.. I've the impression that if you need such a construction your code structure is bad. It's a bit like going to a shoe factory and require shoes for your hands, only because you think you should walk on your hands instead of your feet.. :P TomToad's example is quite a bit oldskool.. ^_^