Answer 1

In this library are cout and cin functions. It means Input Output stream.
https://gcc.gnu.org/onlinedocs/gcc-4.6.2/libstdc++/api/a00911_source.html
See what is inside if you want.

https://gcc.gnu.org/onlinedocs/gcc-4.6.2/libstdc++/api/a00912_source.html
This is what is inside istream.

https://gcc.gnu.org/onlinedocs/libstdc++/libstdc++-html-USERS-3.4/ostream-source.html
And this is what is inside ostream.

In iostream are all input and output functions.

In istream are only input functions.

In ostream are only output functions.