COMP 141 Fall 2019

Program 5: Bottles of a Beverage

Assigned: Monday, October 7
Due: Thursday, October 17, 2019 by 11:55pm

You will write a program to sing the children's (or maybe young adult) song about bottles of a beverage on a wall, with a twist. You may use whatever beverage you want in the song, just keep it PG-13; I don't want any parents calling me asking why I'm encouraging underage drinking or anything like that.

What you need to do

You must write a program that will prompt the user to enter how many bottles they wish to start with on the wall, as well as how many bottles to take off the wall at a time.

Both of these values should be checked to make sure the user enters numbers that are greater than zero for both variables (input validation).
If the user enters an invalid number for either value, print an error message and ask them to re-enter the number.
Do not wait until both variables have been entered to do the checking --- if the first variable entered is negative (for how many bottles to start with), ask them to re-enter it until they get it right before going on to the variable for how many to take off the wall each time.

Then print each verse of the song, taking care that the number of bottles on the wall never becomes negative (it may go to zero, but not below). You do not need to worry about making the song grammatically correct (changing "bottles" to "bottle" or "them" to "it." That's a challenge problem --- see below).

You may assume the user will enter a whole number (an integer), not a float or a string. However, as it says in the paragraph above, if they enter a negative integer or zero, you must ask them to re-enter it until they fix it.

You may design your program in any way you see fit, but you must include a main function that drives the rest of your program. You should follow the guidelines for good programming that we've discussed in class: using comments, choosing appropriate variable names, making use of functions where appropriate, etc.

Sample Interactions

(What the user types is in bold.)

How many bottles should we start with? 0
You must start with a positive number of bottles.  Please re-enter the number.
How many bottles should we start with? -88
You must start with a positive number of bottles.  Please re-enter the number.
How many bottles should we start with? 10

How many do we take off the wall each time? -1
You must remove a positive number of bottles from the wall.  Please re-enter the number.
How many do we take off the wall each time? 0
You must remove a positive number of bottles from the wall.  Please re-enter the number.
How many do we take off the wall each time? 1

10 bottles of pop on the wall, 10 bottles of pop.
Take 1 down, pass them around, 9 bottles of pop on the wall.

9 bottles of pop on the wall, 9 bottles of pop.
Take 1 down, pass them around, 8 bottles of pop on the wall.

8 bottles of pop on the wall, 8 bottles of pop.
Take 1 down, pass them around, 7 bottles of pop on the wall.

7 bottles of pop on the wall, 7 bottles of pop.
Take 1 down, pass them around, 6 bottles of pop on the wall.

6 bottles of pop on the wall, 6 bottles of pop.
Take 1 down, pass them around, 5 bottles of pop on the wall.

5 bottles of pop on the wall, 5 bottles of pop.
Take 1 down, pass them around, 4 bottles of pop on the wall.

4 bottles of pop on the wall, 4 bottles of pop.
Take 1 down, pass them around, 3 bottles of pop on the wall.

3 bottles of pop on the wall, 3 bottles of pop.
Take 1 down, pass them around, 2 bottles of pop on the wall.

2 bottles of pop on the wall, 2 bottles of pop.
Take 1 down, pass them around, 1 bottles of pop on the wall.

1 bottles of pop on the wall, 1 bottles of pop.
Take 1 down, pass them around, 0 bottles of pop on the wall.

Another run:

How many bottles should we start with? 8 
How many do we take off the wall each time? 2

8 bottles of pop on the wall, 8 bottles of pop.
Take 2 down, pass them around, 6 bottles of pop on the wall.

6 bottles of pop on the wall, 6 bottles of pop.
Take 2 down, pass them around, 4 bottles of pop on the wall.

4 bottles of pop on the wall, 4 bottles of pop.
Take 2 down, pass them around, 2 bottles of pop on the wall.

2 bottles of pop on the wall, 2 bottles of pop.
Take 2 down, pass them around, 0 bottles of pop on the wall.

Another run:

How many bottles should we start with? 10
How many do we take off the wall each time? 3

10 bottles of pop on the wall, 10 bottles of pop.
Take 3 down, pass them around, 7 bottles of pop on the wall.

7 bottles of pop on the wall, 7 bottles of pop.
Take 3 down, pass them around, 4 bottles of pop on the wall.

4 bottles of pop on the wall, 4 bottles of pop.
Take 3 down, pass them around, 1 bottles of pop on the wall.

Notice how the last run stops at 1 bottle on the wall, because with taking three down each time, we have to stop there because we don't want to have -2 bottles on the wall.

Your code does not have to follow this exact script verbatim, but all the mentioned functionality should be there: asking the user for number of bottles and how many to remove each time, and printing each verse in turn, stopping before hitting a negative number.

Commments in your code

For every function you write (except main), you must include a comment immediately before the function definition line that contains:

A description of what the function does.
Any parameters the function takes (if any), along with their meanings.
The return value of the function, if there is one, and what it means.

Here's an example you'd use for a function that computes the circumference of a circle:

	# This function computes the circumference of a circle.
	# Parameters: r, the radius of the circle.
	# Returns: the circumference of the circle.
	def circumference_of_circle(r):
	  return 2 * math.pi * r

What to Do

Create a Python program named yourlastname_yourfirstname_prg5.py

Include the standard program header at the top of your Python file.

Follow the comment guide to correctly comment your code.

Submit your Python file on Moodle under Program 5.

Challenge Problem

Make the lyrics grammatically correct for the situations where there is only one bottle on the wall and where the user is removing a single bottle each time.

Grading

Your program will be graded on correctness, as well as on coding style, which refers to choices you make when writing your code, such as good use of variable names, appropriate indentation, and comments (this is not an exhaustive list). See the syllabus for further grading details.

You will receive one bonus point for every complete day your program is turned in early, up to a maximum of five points. For instance, if your program is due on September 20 at 11:59pm, if you turn in your code on Moodle any time on September 19 from 12:00am through 11:59pm, you will receive one extra point on your project. Programs submitted on September 18 from 12:00am through 11:59pm will receive two points. This pattern continues for up to five points.