Problem with for - next

[woki]

Both for loops are endless:

Code: Select all

OpenConsole()
For i.b =0 To -128 Step -1
  PrintN("Wert: "+Str(i.b))
Next i
For i.b =0 To 127
  PrintN("Wert: "+Str(i.b))
Next i
End

[Karbon]

Yep, same here on XP / PB 3.71 Beta 2

[Inner]

Code: Select all

OpenConsole() 
For i =0 To -128 Step -1 
  PrintN("Wert: "+Str(i)) 
Next 
For i =0 To 127 
  PrintN("Wert: "+Str(i)) 
Next
End

this works however.

[GPI]

Code: Select all

OpenConsole() 
For i =0 To -128 Step -1 
  PrintN("Wert: "+Str(i)) 
Next 
For i =0 To 127 
  PrintN("Wert: "+Str(i)) 
Next
End

this works however.

Simple to answer, you have changed i.b to i.l.
The bug only appear, when you use a value at the limit of the range of the variable.

btw: Would be nice, when the debugger can catch this.

[woki]

endless loop: i.w -32768 / 32767
endless loop: i.l -2147483648 / 2147483647

if values are greater or less the loop never executes without any error.

Yes, would be nice, when the debugger can catch this.

[Inner]

Yes I know, it is a bug.. but you see there is no diferents between doing a

loop.b or a loop.l (.l being default) since the limiter in the for...next loop defines the max count value to can go to, the only real diferents is type, long vs byte, don't quite know why anyone would want to loop like you have but still it is a bug.

[Falko]

Sorry,
isn't this fixed or make the Debugger endless bytes in for next?

here this code with Debugger

Code: Select all

For a.b= 1 To 127
  b = a & $FF
  Debug b
Next a

you can see this.

And now:

Code: Select all

For a.b= 1 To 254
  b = a & $FF
  Debug b
Next a

nothing.

[blueznl]

Both for loops are endless:

Code: Select all

OpenConsole()
For i.b =0 To -128 Step -1
  PrintN("Wert: "+Str(i.b))
Next i
For i.b =0 To 127
  PrintN("Wert: "+Str(i.b))
Next i
End

range for a byte: -127 to +127

you're going out of bounds

[blueznl]

And now:

Code: Select all

For a.b= 1 To 254
  b = a & $FF
  Debug b
Next a

nothing.[/quote]

again, bytes are signed in pb, so reach from -127 to +127

[ts-soft]

and why does this not end?

Code: Select all

For a.b= 1 To 127
  b = a & $FF
  Debug b
Next a 

edit: okay, to 126 is ok

[srod]

range for a byte: -127 to +127

I think that a byte can range from -128 to 127. At least the following produces the result of -128:

Code: Select all

a.b = -128
debug a

[Trond]

Both for loops are endless:

Code: Select all

OpenConsole()
For i.b =0 To -128 Step -1
  PrintN("Wert: "+Str(i.b))
Next i
For i.b =0 To 127
  PrintN("Wert: "+Str(i.b))
Next i
End

range for a byte: -127 to +127

you're going out of bounds

No, according to the manual a byte ranges from -128 to +127. He's not out of bounds.

[Falko]

@blueznl, please make following

Code: Select all

For a.b= -129 To 127
  b = a & $FF
  Debug b
Next a

You can see the errormessage from debugger and just this

Code: Select all

For a.b= -128 To 127
  b = a & $FF
  Debug b
Next a

is it ok?

Now this is endless, nothing out of range from -128 to 127.
Out of range is -129 or 255, you can see from debug-message.

[remi_meier]

Not a bug.
Java has the same 'problem':

Code: Select all

for (b = 0; b >= -128; b++)
     ;

A For-Loop is designed like the following:

Code: Select all

Init a.b = 0
|
|
Test a.b >= -128, if false: break
|
|
Decrement a.b
Jump back to Test

So now, when a reaches -128 in 'Test', the loop will be executed and after
the 'Decrement' a will be 127 and 'Test' will be true again. So endless loop.

If Fred would change this, it wouldn't be the standard behaviour of a for-loop
and it would produce some speed decrease...

greetz
Remi

[Falko]

Ok, java can do this. The old GFABASIC makes unsigned from 0 to 255.
I help me with following source, this do that as GFABASIC.

This is better so

Code: Select all

For a.b= -128 To 127
  b = a  ;& $FF  ; This makes 128...255...0...127 and endless
  Debug b+128 ; This makes 0...255
 If a=127:Break:EndIf ; This stopped endless loop
Next a

greetz
Falko