So far we have just used an application with a single user defined class.
Most application do in fact use more than one class.
For example for the first assignment a user defined date class Mydate is defined. This class is used to perform several opperations such as working out wheter a given year is a leep year. A second class, Testdate is also defined. The second class is used to test the functionallity of the mydate class. The advantage of organising things this way is that the mydate class could be used by other programs.