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A friend class is a class that can access the private members of a class as though it were a member of that class.

we can define an entire class as a friend as follow :

Multiple inheritance enables a derived class to inherit members from more than one parent.

When one class inherits from another, the derived class inherits the variables and functions of the base class. 

These variables and functions become part of the derived class.

Static member function means that we  can be called directly by using the class name and the scope operator.

for example :

Static member variable

Static member variable is similar to global variable , but it is applied to class.

Operator overloading allows the programmer to define how operators (such as +, -, ==, =, and !) should interact with various data types. 

Because operators in C++ are implemented as functions, operator overloading works very analogously to function overloading.

Constructor:

Constructors are typically used to initialize member variables of the class to appropriate default values.

In the class , we can define public or private for its data member (or method).

The data member can only be used by method of class if we define the type of data member is public.

In C++, classes are very much like structs, except that classes provide much more power and flexibility.

In C++, when we declare a variable of a class, we call it instantiating the class. The variable itself is called an instance of the class. A variable of a class type is also called an object.

Union is like strucuture but it can only assign one member one time , and a anonymous union is a union without class name .

Anonymous can help us save memory space  , because operation system would allocate the largest memory space of largest

We can use #define to define a constant or a Marco.

for example: (define a constant)

A default parameter is a function parameter that has default value.

The method list() in the File class can help you to achieve this purpose.

Reference is a alias of a variable , it can be used to instead of pointer sometimes.

C++ references differ from pointers in several essential ways:

Sometimes we may generate the functions which have the same function 

but have different argument or return type.

Arithmetic operators (+ , - , * , \ , %)

Relational and euality operators

We can use the modifier , setw , to control the width of output.

cout, clog and cerr are pre-defined objects defined in ostream. 

The iostream class inherits from both ostream and istream

We can use the operator , dec , oct , and hex to decide which format we want.

for example: