This week in lab they should implement inheritance.  They should use
the account class they created last week.  The account class will be
their base class and then they will create a joint_account class which
will be a public derivation of the account class.

1) A constructor should be added to the account class which takes as
parameters the name, the account number, and the starting balance.  

2) Write a class declaration for a derived joint_account class which
is a public derivation of the class account.  It should contain two
private members, the owner's SSN and the joint owner's SSN.  It should
also contain two public functions
 - A constructor for the class should ask the user to enter the two
SSNs and should set these values.
 - A function should be written which allows the user to print the
social security numbers of both owners.

3)Modify the main program to show the use of the new derived joint
account class.

4)Separate files should be used and a makefile should be used.

You should check them off for this program in the lab.  Make sure that
they use separate files and a makefile.