Answer 1

Learning just C and C++ should be fine, although most programmers I've seen have knowledge of multiple languages and actually, it is a good thing to learn more than 1 language (not at the same time though).
Keep in mind that learning *just* the language is not enough. You need to educate yourself in other concepts in programming as well.
As for tips to "learn most effectively in a short time", I'm sorry but there are none. Just like learning anything else, learning computer science is a journey and there are no shortcuts. The most important thing is practise and the more you do that, the better you'll become. Another thing to keep in mind is to keep exploring till your mind settles on the one concept which you want to dig deeper.

Answer 2

Answered here 👇
https://www.sololearn.com/post/358346/?ref=app