Re: The way Basic worked in the old days
> In Basic - there is no labels.
BASIC is not _a_ language, it is a large group of approximately similar, or not so similar, languages. Some do allow labels, even named subroutines.
> Now, if you delete comments at line 20 and 30:
No, no, no, not for any variation of 'BASIC' that I am aware of. For the BASICs that only use line numbers there is _NO_ automatic line renumbering, that would be a complete fail. Deleting lines 20 and 30 would leave lines 40 and beyond with their original line numbers. The whole point of numbering by 10s is so that lines can be inserted, such as 51, 52, etc.
The problem described would arise if the original line 10 had GOTO 30 (which would work correctly) and then lines 20 and 30 were deleted because they were 'merely comments'.