Fabio,

>Where is IDE word ?

Integrated Development Environment. The VFP you use to do development work.

>Alan not write SYS(1104) C++ code, and not test all possible EXE; than it not a proof of the affirmation.

He showed one case where it does, so it is possible. Whether or not it ever returns 0 in your code can not be proven or tested by anyone but you.

>Where is writed that SYS(1104) return 0 at runtime surely ?

Nowhere. And nowhere does it really state that by returning 0 it proves your program is correct either. It is an incorrect assumption of yours that this function proves correctness. There might even be hardware failures that would mean just because your app flushed all of the buffers that the magnetic flux of a diskdrive platter was in fact correctly storing the data.