For lab 4, you will be implementing problems from the textbook. Each problem will be a
function in your main program file.  This main function will present the user with a 
menu to select which problem to run, and then call the appropriate function to present
each problem.

All problems are worth 10 points, extra credit problems are each worth
15 points.  All problems are from Chapter 4 in the text.

Please implement coding exercises 1, 4, 9, 11, and 12 from the
text book.

For extra credit, implement exercises 7, 13.

Make sure you use meaningful variable names, as well as adequate
output to indicate to the user what input is required.

Comments, style, and presentation quality count.

Please email all files to the instructor, after creating a bzip'd
tarball:

Create a directory with your username and copy all files to that 
directory. Then, from the directory  above it, execute 

tar cjvf `whoami`.tar.bz2 `whoami`

This will create a single file archive of all files, to ease
submission. Please note the quotes are backticks (next to the 1 key).