You have seen, in this chapter, how you can have a default constructor call an argument-bearing constructor. You can also have an argument-bearing constructor call another argument-bearing constructor.
Suppose, for example, that all box cars have the same height and
widththey vary only in length. Write a one-argument
constructor for the
box_car class that does all its work
by calling the appropriate
box class constructor.
Next, rewrite the default
box_car constructor such that it
makes use of the one-argument