Answer 1

using namespace std is when u load the standard namespace into your source file.

namespace is when a lot of classes, functions , structures and maybe variables are set into a file.

std is a type of namespace that contains classes for input, output and lots more.

instead of calling std with a scope operator on every cin, cout and endl u come across, you need to include "using namespace std".

example...
without using namespace:-
int age;
std::cout << "how old are you ? << std::endl;
std::cin >> age;
std::cout << "you are " << age << " years old.<< std::endl;

when you use namespace:-
using namespace std;
int age;
cout << "how old are you ? << endl;
cin >> age;
cout << "you are " << age << " years old.<< endl;