Answer 1

iostream include namespace std with include all the classes like cin and cout
iostream is file in which all the code related to cin cout in written in OOP there is concept of namespace to encapsulate classes so we have to use use name space fist.
in c++ to use name space inline we use :: if you hate to write :: after #include statements use following line
using namespace Name_Space_Name; for std
using namespace std;
after add this line you able to use cout with out std::