Answer 1

https://www.sololearn.com/discuss/310869/?ref=app
https://www.sololearn.com/discuss/340041/?ref=app

Answer 2

see namespaces.

if you dont want to type std::cout std::endl etc you specify you want to use the "namespace std (standard)"

that way you just type cout and endl instead

if you know you are only going to be using a few things from the standard namespace you can just specify them

using std::endl;
using std::cout;