Well,
using namespace std;
is likely to not be something looked on as a good thing by most companies.
The best advice is to research a company you are looking at for employment. If at all possible ASK what they would consider desirable with a new hire. And see if they offer an (usually unpaid) internship.
I am a self-taught (still doing it) C++ hobbyist programmer. The best advice I can give? Code, code and code until your brain is mush and your fingers bleed. (Not really, but close).
Most of the code in books and online is either close to be trash, outdated or so rudimentary as to be virtually useless.
There are a couple of free tutorial sites around that are decent, if not comprehensive for what C++ has to offer.
The tutorial here (
http://www.cplusplus.com/doc/tutorial/) is definitely out-dated, no C++14 or later. But then a lot of the core of the basics of C++ are still shown.
Learn C++ (
https://www.learncpp.com/) is being updated, another C++tutorial site that doesn't cover all of what the current C++ standard has to offer. Still lots of good info.
Both sites have examples you can muck around with. Something I highly encourage.
I personally prefer Learn C++.
Online reference site cppreference (
http://en.cppreference.com/w/) has up-to-date info on C++20, the current C++ standard, with examples. But this is not a site to learn C++. It is a very technical reference oriented site.
There is one book I do recommend as one to learn from as well as being a good reference, covers a lot of what is now considered Modern C++, including C++20.
Beginning C++20: From Novice to Professional
https://www.amazon.com/gp/product/1484258835/
I recently purchased it (I have several dozen C++ books, print and eBook) and it is one of the better "Learn C++" books I own. Other books are specific to a specific C++ standard or part of the language, such as lambdas. Or were written for earlier C++ standards.
Older code I run across (or is part of one of the "Learn C++ books I own) I "revisit" and see what it might take to update it for later standards. It certainly isn't boring, and doing it makes me think.
What works for me may not work best for you, after all I am not someone who is programming employment oriented. For me learning C++ is a hobby. Intellectual curiosity. If I have any goals they might be to throw together some code to create games. Both console and WinAPI GUI.