1. The declaration tells the compiler the type and name of something, but omits details. The definition will need to provide details.
2. size_t is a typedef, some type unsigned by calculating the number of C ++.
3. The initialization process is the initial target of giving. For user-defined objects, initialization is executed by the constructor.
4. explicit constructor can be prevented from performing implicit type conversion, but can still perform an explicit type conversions.
The copy constructor is used to initialize the self-object is the same type of objects, for copying copy assignment operator from another object values to the same type of self-object. If a new object is defined, then there will be a constructor is called. If no new object is defined, then the call is copy assignment operator.
6. passed by value in a manner not user-defined type, should be transmitted by way of a constant reference.