File Input/Output and Pmatrices

In this chapter we will develop a program that reads and writes files, parses input, and demonstrates the pmatrix class. We will also implement a data structure called Set that expands automatically as you add elements.

Aside from demonstrating all these features, the real purpose of the program is to generate a two-dimensional table of the distances between cities in the United States. The output is a table that looks like this:

The diagonal elements are all zero because that is the distance from a city to itself. Also, because the distance from A to B is the same as the distance from B to A, there is no need to print the top half of the matrix.