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When you define a class, you tell C++ about the variables that describe
the objects that belong to that class. Note that you also can define
functions that work with those objects. You might, for example, define a
volume function that knows how to find values for any box-car
object's height, width, and length variables, and that
knows how to use those values to compute the box-car object's volume.
Thus, in the following diagram, the box_car class description
contains descriptions of variables and class-specific functions, whereas
the descriptions of particular box_car objects contain variables
values.
*-----------------------------------------------*
| Description of variables; | <-- Description of
| for example, height, width, and length | the box_car
| Description of class-specific functions; | class
| for example, volume |
*-----------------------------------------------*
^ ^ ^
| Instance of | Instance of | Instance of
| | |
*-------------* *-------------* *-------------*
| height 10.5 | | height 10.5 | | height 10.5 | <-- Descriptions of
| width 9.5 | | width 9.5 | | width 9.5 | particular
| length 40.0 | | length 40.0 | | length 50.0 | box_car objects
*-------------* *-------------* *-------------*