> You think it isn't possible to become a decent C++ programmer ... using only online tutorials?
That really depends on what you call decent, and how good your tutorials are. You could probably achieve your aims with a few good tutorials.

Fact is, you're never going to get that far with a single source of information. Just as code has bugs and missing features, tutorials, books, other people all have gaps and errors in the knowledge. C++ is far too vast to be captured in any single book or tutorial.

Open forums like this allow you to test your knowledge against other people, who in turn may be corrected themselves. Somewhere along the line a "good" answer usually emerges. If you just have a single source, there's no way to check what you're using is good, even it it does seem to work for you.

Oh, and practice practice practice your skills.