Homework 0 - Pizza Calculator

Objectives

Reminder: For all projects, BEFORE you start coding, READ THROUGH THE ENTIRE SPECIFICATION and think through at a high level how your full solution will look. Then start coding.

• Verify you have the basic prerequisite knowledge for the class
• Practice basic Python Syntax
  • variables & basical arithmetic operators
  • conditionals & boolean expressions
  • console I/O
  • simple string formatting

In this first Homework, you will be using a few variables, conditionals, and working with input and output. It is also your opportunity to become familiar with the Python language and interpreter, exactly following specifications, how to submit assignments, and our autograder.

None of the programming concepts in this assignment should be new to you if you have prior programming experience. All that might be new is the Python syntax which we've covered in class. If you are struggling with the programming concepts in this assignment, you should consider switching to CS 110.

Introduction

You have been elected as President of the Pizza Council of BYUSA. Your primary responsibility is to determine how many pizzas should be ordered when BYUSA holds an event. To make things easier, you decide to write a Python program to help you do the calculations.

The program will first prompt the user to enter the number of people to be fed and later prompt them to enter the tip percentage to pay the delivery person. The program will calculate the number of large, medium, and small pizzas needed. Based on those numbers, it will then cacluate the total price (including tip), and just for fun, the total number of square inches of pizza ordered and average square inches per person.

Special Notes

Output format

For this lab, the autograder will check to see that your output exactly matches with what is expected. Since we are checking your output against a specific set output, we’ll provide you the exact prompts to use when you prompmt the user for input and output. In future assignments, that will often be left up to you. Please pay attention to spacing, spelling, and punctuation, and other details in these prompts.

Constants and Magic Numbers

This lab will help you gain experience using constant variables in your code and avoiding the use of magic numbers (magic numbers refers to a number that is used in the code without any explanation of its meaning). While Python doesn't really have constant values, we use a special naming convention to signify that a varaiable should not be changed. We do this using "upper snake case." In upper snake case, all characters are capitalized and underscores - "_" - connect the words. For example, to declare constants for the value of pi and the people per large pizza, the code would look like this:

PI = 3.14159265
PEOPLE_PER_LARGE = 7

Constants should typically be declared at the top of the file (outside of any functions). They are usually found directly under the import statements in a Python file.

The instructions below specify the exact name that should be used for the nine pizza related constant values used in this project. It is important that for this assignment, you use the names given. If you don't, the autograder will not be able to fully grade your assignment and you will not recieve full credit.

Numerical precision

The number of each type of pizzas are integers and should be printed as such. The areas, and costs should be displayed with two decimal places. Note that to round correctly in this assignment you might want to use the special syntax for a placeholder (where a variable would go) in a formatted string to round your values to two decimal places (this method will ensure you don't lose trailing zeroes when you print your output). This method looks something like this:

{your_variable_name:.2f}

The ":" introduces a modifier to the string and the .2f indicates we want to modify it to a fixed point number with two decimal places.

Pizza Data

The following table provides information about the various sized pizzas that you’ll need to implement this assignment.

Part 1 - Getting Started

To get started on this homework you should download homework00.zip and extract the contents into a new directory. The contents of the file are:

• homework0.py - this is the file you will edit and turn in for grading
• test_homework0.py - this is a test file you can use to verify that your code is running correctly. This is the exact test script that the autograder will run when you submit your code.
• test_files directory - This directory contains the expected output for the test script annotated for the test to evalulate. You can look at these files if you get stumped but be aware that they contain extra code that you should not be outputting.

Once you've extracted the files, open the directory as a new project in your IDE. Then verify that you can run the test_homework0.py file. If you set up your environment properly during Lab 00, it should run. All the tests will fail as your homework0.py file is empty, but as long as the tests ran you are good to go. If you get a "Traceback" error, something isn't working and you should check with a TA to get your environment set up correctly.

Part 2 - Implementation

In this part, you will write the code for the program. In this homework, we walk you through the steps, but you should have a good idea of how to write the code for each part already based on the specification above. The tasks below model the concepts of Stepwise refinement and incremental development which we'll talk about in a future lecture.

Sample output for the program can be found at the bottom of the instructions, so you can verify that you are implementing things properly as you go. You can also run the test script to verify your code as implement each part.

Task 1 - Count your Many Pizzas (15 pts)

In this part of the lab, you’ll prompt the user for the number of guests and then compute the number of large, medium, and small pizzas needed.

Start by defining three constants for the number of people fed by each size of pizza. These constants should be PEOPLE_PER_LARGE, PEOPLE_PER_MEDIUM, and PEOPLE_PER_SMALL. Then prompt the user for how many guests to order pizza for. The prompt to the user should be:

Please enter how many guests to order for:

Once the user has provided their input, compute the number of large, medium, and then small pizzas you need to order for there to be exactly enough pizza for everyone. For example if you have 9 people to order for, ordering two large pizzas is too much, you would need 1 large and two small.

Hint, use Python's floor division (//) and modulus (%) operators.

Once you’ve determined the number of pizzas to order, report that to the user with the following output:

<NN> large pizzas, <NN> medium pizzas, and <NN> small pizzas will be needed. 

where the <NN>s are replaced by the number of that size of pizza. If no pizzas of that size are need just print 0 (zero) for the number.

Task 2 - Serving Size (15 pts)

Just for fun we’ll compute the total number of square inches of pizza ordered and how many square inches of pizza each person gets.

Start by declaring four new constants, one for PI (use the exact value given in the Special Notes section above), and three for the diameters of the various pizzas. The constants for the diameters should be DIAMETER_LARGE, DIAMETER_MEDIUM, and DIAMETER_SMALL.

Next compute the total area of pizza (in square inches) you need to order.

Then compute the total area of pizza (in square inches) each guest can eat.

Report these values with a precision of two decimal places to the user with the following output:

A total of <NN.NN> square inches of pizza will be ordered (<NN.NN> per guest). 

where <NN.NN> is the size computed. There should be an empty line between this output and the output from Task 1 and between the output for this task and Task 3 below.

Task 3 – Paying the Piper (10 pts)

Finally, we need to compute the cost of the pizzas. We’re also going to give the delivery driver a tip.

Start by defining your final three constants to represent the cost of each size pizza. These constants should be COST_LARGE, COST_MEDIUM, and COST_SMALL.

Then prompt the user for the percent of the total price to be paid as a tip. The tip percentage will be input as a whole integer from 0 to 100. The prompt to use is:

Please enter the tip as a percentage (i.e. 10 means 10%):  

Once the tip amount has been provided, compute and report the total cost (including tip) of all the pizzas. The output should look like this:

The total cost of the event will be: $<NN.NN> 

Where <NN.NN> is the total cost of the pizzas and tip combined.

Task 4 - The "Magic" of Avoiding Magic Numbers (10 pts)

Sometimes it may feel like a nuisance to make sure to properly use constants for magic numbers, so here we give you the opportunity to see how useful it can be. By changing just some of the constants, your program can simulate any pizza sizes and prices, without having to touch any other part of your code. Those constants are how many people each pizza feeds, the diameters of each pizza, and the cost of each pizza. Make sure that you have written your code so that by changing only those nine values, you can simulate any arbitrary pizza values.

Try this out yourself by changing just the values of the constants at the top of the program to the following new values:

Now that you've changed the values of the constants, run the program again. You should see that the program still works correctly, but now with the new values. You can compare to the sample output below.

Be sure to change your constant values back to the original ones in the Pizza Data section above before submitting to the autograder.

If you've written your code properly, the autograder will change the values of those constants and test your code with different values. If everything is working, you're already passing the final tests. If you've hard-coded any of those values in your calculations, you will not pass the tests and lose points. Remember, you need to have used the exact names for the constants given above for this to work.

Sample Input and Output

When you run the program in the case where there are 303 guests and you want to give a 15% tip, the interaction will look like:

Please enter how many guests to order for:303
43 large pizzas, 0 medium pizzas, and 2 small pizzas will be needed. 

A total of 13735.04 square inches of pizza will be ordered (45.33 per guest). 
Please enter the tip as a percentage (i.e. 10 means 10%):15
The total cost of the event will be: $742.67.

The output with the second set of constants, for the same input, would be:

Please enter how man guests to order for:303
33 large pizzas, 1 medium pizzas, and 1 small pizzas will be needed.

A total of 15337.26 square inches of pizza will be ordered (50.62 per guest).
Please enter the tip percentage (i.e. 10 means 10%):15
The total cost of the event will be: $623.74.

As a second check that your code is working okay before submitting it, using the inputs of 20 guests and 12% tax you should get the following output values:

Turn in your work

You'll submit your homework0.py file on Canvas via Gradescope where it will be checked via the auto grader. We will be testing your program using several different sets of constants. Make sure that you haven't "hard coded" anything specific to your data.