Why do we write ' using namespace std; '?

Why do we write ’ using namespace std; ’ in the beginning of each program??
and we used to write #include<iostream.h> while using turbo C++ but here we don’t, why so??

Hello @aayushitalwar02 refer this for namespace:

no here also we have to include the header files.

I hope I’ve cleared your doubt. I ask you to please rate your experience here
Your feedback is very important. It helps us improve our platform and hence provide you
the learning experience you deserve.

On the off chance, you still have some questions or not find the answers satisfactory, you may reopen
the doubt.