Which library I should include in order to use "cin" and "cout" object ?

you must use #include iostream.h

#include <conio.h> use in programming for cout and cin  process

You have to Include the Input Output Stream, i.e. #include<iostream> or #include<iostream.h> ".h" is the extension for the header files as "iostream" is a header file that's why it has the extension ".h".

You must use #include iostream.h for input and output

The .h indicates that it is a header file

#include<iostream> should be used