Astack is a type of data collection on which things can be "pushed" and "popped". for example, a stack of plates can have a plate added (or "pushed") onto the stack, and a plate removed (or "popped") from the stack. plates are pushed onto or popped off of the stack one at a time. the last plate pushed onto the stack is the first plate popped off of the stack. this type of structure is known as "lifo" – last in, first out.

in this project, you will create a stack that will hold objects of type person. the stack itself will be in a class named personstack.

when manipulating the stack, three types (or classes) of exceptions can be thrown. each exception class will contain two constructors, one which provides a default message for the exception, and one which takes a string as an argument and sets the exception message to that string.

the three exception classes in this project are: