Cash

Implement a program that calculates the minimum number of coins required to give a user change.

$ python cash.py
Change owed: 0.41
4

Getting Started

Log into code.cs50.io, click on your terminal window, and execute cd by itself. You should find that your terminal window’s prompt resembles the below:

Next execute

wget https://cdn.cs50.net/2022/fall/psets/6/sentimental-cash.zip

in order to download a ZIP called sentimental-cash.zip into your codespace.

Then execute

unzip sentimental-cash.zip

to create a folder called sentimental-cash. You no longer need the ZIP file, so you can execute

rm sentimental-cash.zip

and respond with “y” followed by Enter at the prompt to remove the ZIP file you downloaded.

Now type

cd sentimental-cash

followed by Enter to move yourself into (i.e., open) that directory. Your prompt should now resemble the below.

sentimental-cash/ $

Execute ls by itself, and you should see cash.py. If you run into any trouble, follow these same steps again and see if you can determine where you went wrong!

If you’d like to open this problem in CS50 Lab, you can right-click or control-click on the sentimental-cash folder and choose “Open in CS50 Lab”. You should see the specification for this problem on the left-hand side and its distribution code on the right-hand side.

Specification

Write, in a file called cash.py, a program that first asks the user how much change is owed and then spits out the minimum number of coins with which said change can be made. You can do this exactly as you did in Problem Set 1, except that your program this time should be written in Python, and you should assume that the user will input their change in dollars (e.g., 0.50 dollars instead of 50 cents).
Use get_float from the CS50 Library to get the user’s input and print to output your answer. Assume that the only coins available are quarters (25¢), dimes (10¢), nickels (5¢), and pennies (1¢).
- We ask that you use get_float so that you can handle dollars and cents, albeit sans dollar sign. In other words, if some customer is owed $9.75 (as in the case where a newspaper costs 25¢ but the customer pays with a $10 bill), assume that your program’s input will be 9.75 and not $9.75 or 975. However, if some customer is owed $9 exactly, assume that your program’s input will be 9.00 or just 9 but, again, not $9 or 900. Of course, by nature of floating-point values, your program will likely work with inputs like 9.0 and 9.000 as well; you need not worry about checking whether the user’s input is “formatted” like money should be.
If the user fails to provide a non-negative value, your program should re-prompt the user for a valid amount again and again until the user complies.
Incidentally, so that we can automate some tests of your code, we ask that your program’s last line of output be only the minimum number of coins possible: an integer followed by a newline.

Usage

Your program should behave per the example below.

$ python cash.py
Change owed: 0.41
4

Testing

While check50 is available for this problem, you’re encouraged to first test your code on your own for each of the following.

Run your program as python cash.py, and wait for a prompt for input. Type in 0.41 and press enter. Your program should output 4.
Run your program as python cash.py, and wait for a prompt for input. Type in 0.01 and press enter. Your program should output 1.
Run your program as python cash.py, and wait for a prompt for input. Type in 0.15 and press enter. Your program should output 2.
Run your program as python cash.py, and wait for a prompt for input. Type in 1.60 and press enter. Your program should output 7.
Run your program as python cash.py, and wait for a prompt for input. Type in 23 and press enter. Your program should output 92.
Run your program as python cash.py, and wait for a prompt for input. Type in 4.2 and press enter. Your program should output 18.
Run your program as python cash.py, and wait for a prompt for input. Type in -1 and press enter. Your program should reject this input as invalid, as by re-prompting the user to type in another number.
Run your program as python cash.py, and wait for a prompt for input. Type in foo and press enter. Your program should reject this input as invalid, as by re-prompting the user to type in another number.
Run your program as python cash.py, and wait for a prompt for input. Do not type anything, and press enter. Your program should reject this input as invalid, as by re-prompting the user to type in another number.

Execute the below to evaluate the correctness of your code using check50. But be sure to compile and test it yourself as well!

check50 cs50/problems/2022/fall/sentimental/cash

Execute the below to evaluate the style of your code using style50.

style50 cash.py

How to Submit

Download your cash.py file by control-clicking or right-clicking on the file in your codespace’s file browser and choosing Download.
Go to CS50’s Gradescope page.
Click “Problem Set 6: Sentimental (Cash)”.
Drag and drop your cash.py file to the area that says “Drag & Drop”. Be sure it has that exact filename! If you upload a file with a different name, the autograder likely will fail when trying to run it, and ensuring you have uploaded files with the correct filename is your responsibility!
Click “Upload”.

You should see a message that says “Problem Set 6: Sentimental (Cash) submitted successfully!” You may not see a score just yet, but if you see the message then we’ve received your submission!

Per Step 4 above, after you submit, be sure to check your autograder results. If you see SUBMISSION ERROR: missing files (0.0/1.0), it means your file was not named exactly as prescribed (or you uploaded it to the wrong problem).

Correctness in submissions entails everything from reading the specification, writing code that is compliant with it, and submitting files with the correct name. If you see this error, you should resubmit right away, making sure your submission is fully compliant with the specification. The staff will not adjust your filenames for you after the fact!