On 06/07/2021 14:13, Wolfgang Lenerz via Ql-Users wrote:
Hi Per,
an interesting pitfall, thanks for pointing that out.
It does seem that Qlib sets the value of the repeat loop control
variable to 0 at the start of the loop.
Do you know how this fares on plain QDOS, not SMSQE?
Regards
Wolfgang
I dont know if this has been documented anywhere, but Im putting it out
here as it caused me some grief.
It appears that Q-Liberator zeroes the loop variable on entry to a loop.
The following demo, which is acceptable (although perhaps not very
elegant) S*BASIC, will not work in the same way once compiled with Qlib.
100 loop = 3
110 cnt = 0
120 PRINT 'Start:'! loop, cnt
130 REPeat loop
140 PRINT loop, cnt
150 cnt = cnt + 1
160 IF cnt >= loop: EXIT loop
170 END REPeat loop
180 PRINT 'End:'! loop, cnt
190 PAUSE: QUIT
In the Qlib-compiled version the loop is exited after a single run as
the condition cnt >= loop is met immediately, to wit 1 >= 0
The worrying part of this is that while I was figuring out what was
wrong, running an embedded routine like this many times, the system
crashed due to memory corruption. Whether this was due to the SBASIC or
Qlib compiled version I cant say right now. So just beware and keep on
progging!
NB: This works, though. As long as you start out with loop = 0
100 loop = 0
110 cnt = 3
120 PRINT 'Start:'! loop, cnt
130 REPeat loop
140 PRINT loop, cnt
150 loop = loop + 1
160 IF loop >= cnt: EXIT loop
170 END REPeat loop
180 PRINT 'End:'! loop, cnt
190 PAUSE: QUIT
I tested it under Qdos JS and both loops work exactly like in Qlib!
Minerva, as one might have guessed, behaves like SBASIC. Clearly the
smarter approach (why forbid something when it doesnt matter, and
which might even come in handy?) but since its not consistent across
the board, its best avoided.
Bob, Dilwyn: I only discovered this by chance, due to a spelling mistake.
Per
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