Answer 1

c++ standard library has there default function or method to work with our code (with define object name , that we use ex:- Rand() this is also a object of class <cstdlib> which include function member of c++)to use this we have to include that header file you will easily understand by going classes and objects in this tutorial.
c++ standard library features depend on there object's defined members and function and it's different/same with each object we use .