Homework 3, Item 4
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This exercise, as a homework question, is mainly about loops, not arrays. I
had 2 objectives when I assigned it:

* Get you to work with some array code before we talk about it in class.

* Apply the various looping concepts we talked about in class before you use
  some of them in Lab 3.


The first step, which I hope is obvious, is to copy, compile, and run Program
7.2 on page 101. Be sure you understand how the 2nd loop works.

Now, entering 20 numbers each time you run the program gets tiresome
(quickly!), so how could you allow a user to bail out, or exit early (other
than Ctrl-C)? Use the special response of 999 as suggested in the exercise.

The author gives you a huge hint regarding the break statement, so try adding
a break statement so the user can quit sooner than 20 numbers.

Then, when that works, change the for loop so the user could enter any number
of responses, but quit when she enters 999.