The Using keyword can be used for the using directives and the using declarations.

The difference is using directive allows all names in a namespace to be used as if they are normal names.

A using declaration, on the other hand, enables the program to use an individual name from a namespace without qualifying it with the namespace qualifier.

It is necessary to understand some of the concepts used extensively in object oriented programming.These include

1. Objects
2. Classes
3. Data abstraction and encapsulation
4. Inheritance
5. Polymorphism
6. Dynamic Binding
7. Message passing

Names in a normal namespace can be used outside of the translation unit where the namespace is declared.

Names in an unnamed namespace can only be used within the translation unit where the namespace is declared.

Yes, we can use names defined in a namespace by prefixing them with the namespace qualifier

The standard namespace stdis defined by the C++ Standard Library. It includes declarations of all names in the Standard Library.

We have two formats for initializers in c++ .One is regular C notation and another one is contstructor notation. For Ex:

int abc = 123;
int abc(123);

We can link c++ programs by using extern "C" linkage specification around the c function declarations.

Well its a member function that the base class forces the derived classes to provide. Normally these member functions have no implementation. Pure virtual functions are equated to zero.

class Shape { public: virtual void draw() = 0; };

Main advantage of external iterator is it can be active many difference iterators simultaneously on the same subject.

The function acts as a friend to a class. It can access its private and protected members as a friend of a class.
It must be listed in the class definition but its not a member of the class.