631: Mainline

The main function in the version of analyze_train shown in Segment 627 reads serial numbers from the standard cin stream, which you know you can attach to a file using a command-line argument. Suppose that you want to make the following changes:

• You want your program to ask for a file name, which you type in after your program is called. Thus, there is to be no command-line argument.
• You want to move the bulk of the work from the main function into a new function, do_analysis, in preparation for doing the analysis repeatedly.
• You want your new main function to call on do_analysis whenever you type a file name.