20. Encapsulation in C++

A requirement that data and logic be packaged separately in distinct objects

The notion that data and logic can be packaged together and passed around within a program as a single object.

The restriction that logic within a particular object can only operate on data stored within that same object.

Require that the data type of the output will be the same as that of the input.

Ensure the user cannot do anything to change the private attributes of the object.

Pass in constant attribute values to the accessor function.

Ensure that only class member functions have access to private class attributes.

Invoke logic that checks whether the input data are valid before setting attributes.

Prevent users from changing non-public class attributes.