Using namespace std; for what it is use? I can't get it.

Answer 1

Namespaces were introduced in c++ to resolve identifier/ variable name conflicts. This ensured that two objects can have the same name and yet be treated differently if they belonged to different namespaces. Std is a namespace which contains so many predefined identifiers like cout, cin, string, vector etc.
If we don't write "using namespace std" and use a statement - cout<<"hello"; in our code then compiler would treat cout as undeclared variable and would throw an error. So, basically , "using namespace std" tells the compiler to check std namespace when resolving the undeclared identifiers.
std::cout<<"hello"; would also work.

Answer 2

" Namespaces are used to organize code into logical groups and to prevent name collisions that can occur especially when your code base includes multiple libraries" source: " https://docs.microsoft.com/en-us/cpp/cpp/namespaces-cpp?view=vs-2019 ". They are similar to python's import statements in that they allow you to access code from other libraries.

Answer 3

It imports all the items in the standard namespace located in the standard library. Without it you would have to type std:: in front of any std library member that you need to use, EG. std::cout std::endl std::string etc...
You can create your own namespaces which can lead to bugs if you use the std namespace. See TheCherno on youtube, he has an excellent c++ course where he explains it well.