What is "iostream" and it's significance? Also difference between "iostream and iostream.h"

Answer 1

<iostream> header is included to provided access to input and output standard objects such as cin and cout, which are provided by the headers <istream> (input stream) and <ostream> (output stream) respectively, both of which are included in <iostream>

http://www.cplusplus.com/reference/istream/istream/
http://www.cplusplus.com/reference/ostream/ostream/

<iostream.h> is similar to <iostream> but obsolete, used during the pre-standard C++ era.

Answer 2

its like a library really, once declared,, the compiler will know to load inputs and outputs aswell as a few other things like strings

Answer 3

iostream is header file or library which consist object like CIN and COUT for input and output purpose and in some compiler like turbo c++ we have to add .h in iostream because it support on this format while other compiler like DEV C++ and CODEBLOCk do not reqire .h extension