Assignment 3: Loops, I did it again!

Due Friday, march 12, before midnight

The goals of this assignment are:

Work with loops
Work with if statements
Work with accumulator variables

1. Grandma’s Pies

Write a program, Pies.java, which prints messages about your ancestor’s pies. Your program should ask for a number of ancestors and then print messages about each ancestor’s Pies.

Two examples of the running program are shown below. User input is shown in bold.

$ java Pies
Enter a number: 0

$ java Ancestor
Enter a number: 1

My grandmother's pies are the best!

$ java Ancestor
Enter a number: 6

My grandmother's pies are the best!
My great grandmother's pies are the best!
My great great grandmother's pies are the best!
My great great great grandmother's pies are the best!
My great great great great grandmother's pies are the best!
My great great great great great grandmother's pies are the best!

You may assume that the user only inputs valid numbers.

2. Digital pet

Write a program, Pet.java, that simulates a virtual pet. Each day you must feed your pet. Your pet starts with a weight of 100 pounds. You start with 100 food pellets. The user should specify how many days to simulate your virtual pet.

Each day, your pet burns between 10 and 20 pounds.
When your feed your pet, your food gives between 0 and 2 times the pounds.

Below is an example

$ java Pet
Your pet weighs 100 pounds
You have 100 pellets
Enter the number of days: 3

Day 1
Your pet lost 10 pounds and now weighs 90 pounds
How many pellets do you want to feed your pet? 10
You fed your pet 10 pellets
Your pet gained 10 pounds and now weighs 100 pounds
You have 90 pellets left

Day 2
Your pet lost 11 pounds and now weighs 89 pounds
How many pellets do you want to feed your pet? 50
You fed your pet 50 pellets
Your pet gained 100 pounds and now weighs 189 pounds
You have 40 pellets left

Day 3
Your pet lost 14 pounds and now weighs 175 pounds
How many pellets do you want to feed your pet? 20
You fed your pet 20 pellets
Your pet gained 0 pounds and now weighs 175 pounds
You have 20 pellets left

Requirements and tips:

To compute the amount of pounds lost per day, you need to generate a random number between 10 and 20 (inclusive).
To compute the amount of pounds gained per pellet, you need to generate a random number between 0 and 2 (inclusive). Then multiply the number of pellets by this number.
The user should not be allowed to feed their pet more pellets than they have! Check whether the requested amount is too much and adjust it if it is.
Your pet’s weight should not go below zero! Check for a negative weight and clamp it to zero.
If you personalize your pet, be sure to point this out in your readme!

Below the user tries to feed more pellets than they have available:

$ java Pet
Your pet weighs 100 pounds
You have 100 pellets
Enter the number of days: 2

Day 1
Your pet lost 18 pounds and now weighs 82 pounds
How many pellets do you want to feed your pet? 300
Not enough pellets! We will feed 100 pellets
You fed your pet 100 pellets
Your pet gained 0 pounds and now weighs 82 pounds
You have 0 pellets left

Day 2
Your pet lost 13 pounds and now weighs 69 pounds
How many pellets do you want to feed your pet? 100
Not enough pellets! We will feed 0 pellets
You fed your pet 0 pellets
Your pet gained 0 pounds and now weighs 69 pounds
You have 0 pellets left

Below the pet’s weight goes to zero.

$ java Pet
Your pet weighs 100 pounds
You have 100 pellets
Enter the number of days: 6

Day 1
Your pet lost 20 pounds and now weighs 80 pounds
How many pellets do you want to feed your pet? 0
You fed your pet 0 pellets
Your pet gained 0 pounds and now weighs 80 pounds
You have 100 pellets left

Day 2
Your pet lost 20 pounds and now weighs 60 pounds
How many pellets do you want to feed your pet? 0
You fed your pet 0 pellets
Your pet gained 0 pounds and now weighs 60 pounds
You have 100 pellets left

Day 3
Your pet lost 20 pounds and now weighs 40 pounds
How many pellets do you want to feed your pet? 0
You fed your pet 0 pellets
Your pet gained 0 pounds and now weighs 40 pounds
You have 100 pellets left

Day 4
Your pet lost 20 pounds and now weighs 20 pounds
How many pellets do you want to feed your pet? 0
You fed your pet 0 pellets
Your pet gained 0 pounds and now weighs 20 pounds
You have 100 pellets left

Day 5
Your pet lost 20 pounds and now weighs 0 pounds
How many pellets do you want to feed your pet? 0
You fed your pet 0 pellets
Your pet gained 0 pounds and now weighs 0 pounds
You have 100 pellets left

Day 6
Your pet lost 20 pounds and now weighs 0 pounds
How many pellets do you want to feed your pet? 0
You fed your pet 0 pellets
Your pet gained 0 pounds and now weighs 0 pounds
You have 100 pellets left

3. Poll predictor

credit: Deepak Kumar

Write a program, Predictor.java, which predicts a candidate’s likelihood of victory given its current polling number and margin of error. For example, if a poll predicts that a candidate has a 47% chance of winning a state with a 6% margin of error, can we make an overall prediction that the candidate will win a state?

One way to do this is to simulate an actual vote incorporating the margin of error. Let’s say, a poll (POLL) in a state shows that a candidate is likely to receive 47% of the vote in their favor with a margin of error +/- 6% (MOE). With this information, we can do a simulation of the state’s voting, and arrive at the % of votes received by the candidate in a poll:

SamplePoll = POLL + X * MOE

Where X is a number in the range [-1.0..1.0]. For example, if X is -0.5, then the candidate will receive 0.47 + -0.5 * 0.06 = 0.44. This means, in this instance, the candidate received only 44% of the votes (i.e. losing the state). Alternately, if X turns out to be 0.8 then the candidate will receive 0.47 + 0.8 * 0.06 = 0.518 or 51.8% of the votes cast thereby winning the state.

We can use Java’s Math.random() function to generate values of X in the range [-1.0..1.0) and perform a simulation of several sample elections based on POLL and MOE to see if a candidate is likely to win or lose a state. For example,

$ java-introcs Predictor Keystone 0.47 0.06 1000000
Candidate win likelihood for Keystone state is 25.02%

The above means that after performing 1 million randomized simulated polls based on POLL and MOE the candidate has a 25% likelihood of winning Keystone state. Here are some more examples.

$ java-introcs Predictor Keystone 0.53 0.06 1000000
Candidate win likelihood for Keystone state is 74.99%

$ java-introcs Predictor Golden 0.49 0.07 1000000
Candidate win likelihood for Golden state is 42.82%

$ java-introcs Predictor Nutmeg 0.51 0.02 1000000
Candidate win likelihood for Nutmeg state is 75.01%

You program, Predictor.java, should take the following command line arguments:

state: (String) state name. For example, Keystone, Golden, or Nutmeg
POLL: (double) polling number, a double in the range [0,1]. For example, 0.53, 0.49, or 0.51
MOE: (double) margin of error, a double in range [0,1]. For example, 0.06, 0.07, or 0.02
N: (int) number of simulation iterations. For example, 1000000

Your program, Predictor.java, should implement the following algorithm

wins = 0
Repeat N times
   Compute SamplePoll = POLL + randomNumber * MOE
   If SamplePoll > 0.5 then
       Increment wins by 1
   Compute and output overall win likelihood = (wins/N)

Table 1. Poll data
STATE	Poll	Margin of Error
Garden	48%	3%
Empire	53%	4%
Nutmeg	42%	9%
Golden	52%	4%
LoneStar	49%	5%

In your writeup, include the likelihoods computed by your program for all states, using N = 1000000.

Pretty printing is implemented using StdOut.printf as described in section 1.5 of your textbook. Using printf requires that you compile with the command javac-introcs and run with the command java-introcs.

4. What to hand-in

The programs, Pies.java, Pet.java, Predictor.java.
Make sure each program has a header containing your name, date, and purpose of the program
A brief write-up containing your name, assignment number, and a few sentences about how long you spent on the assignment and any interesting bugs you solved. Don’t forget to include the likelihoods computed by your Predictor!

4.1. How to hand-in

Copy your programs and writeup to your dropbox, into the folder called A03.