Answer 1

Manav Roy
Standard Library is a collection of classes and functions, which are written in the core language and part of the C++ ISO Standard itself. The C++ Standard Library provides several generic containers, functions, strings, for support the language specifications.
Where as STL means Standard Template library, which boosts many parts of the C++ Standard Library. It provides four components called algorithms, containers, functions, and iterators and added in 1994, I think. So <string> library is there in c++ from core. Not from STL.

Edit:

See this link for various c++ standard libraries and STL..
https://www3.ntu.edu.sg/home/ehchua/programming/cpp/cp9_STL.html

2.7 , 2.8 will answer your question.
I hope this clears..
and
https://www.tutorialspoint.com/What-s-the-difference-between-STL-and-Cplusplus-Standard-Library

Answer 2

<array> is part of STL.
<string> class is a standard library there before STL features, but have implementation support by STL features. Like iterators, .. find(), search() algarithms...