Implement a program that runs a plurality election, per the below.
$ ./plurality Alice Bob Charlie Number of voters: 4 Vote: Alice Vote: Bob Vote: Charlie Vote: Alice Alice
Elections come in all shapes and sizes. In the UK, the Prime Minister is officially appointed by the monarch, who generally chooses the leader of the political party that wins the most seats in the House of Commons. The United States uses a multi-step Electoral College process where citizens vote on how each state should allocate Electors who then elect the President.
Perhaps the simplest way to hold an election, though, is via a method commonly known as the “plurality vote” (also known as “first-past-the-post” or “winner take all”). In the plurality vote, every voter gets to vote for one candidate. At the end of the election, whichever candidate has the greatest number of votes is declared the winner of the election.
Here’s how to download this problem’s “distribution code” (i.e., starter code) into your own CS50 IDE. Log into CS50 IDE and then, in a terminal window, execute each of the below.
cdto ensure that you’re in
~/(i.e., your home directory).
mkdir pset3to make (i.e., create) a directory called
pset3in your home directory.
cd pset3to change into (i.e., open) that directory.
mkdir pluralityto make (i.e., create) a directory called
cd pluralityto change into (i.e., open) that directory.
wget https://cdn.cs50.net/2020/fall/psets/3/plurality/plurality.cto download this problem’s distribution code.
ls. You should see this problem’s distribution code, in a file called
Let’s now take a look at
plurality.c and read through the distribution code that’s been provided to you.
#define MAX 9 is some syntax used here to mean that
MAX is a constant (equal to
9) that can be used throughout the program. Here, it represents the maximum number of candidates an election can have.
The file then defines a
struct called a
candidate has two fields: a
name representing the candidate’s name, and an
votes representing the number of votes the candidate has. Next, the file defines a global array of
candidates, where each element is itself a
Now, take a look at the
main function itself. See if you can find where the program sets a global variable
candidate_count representing the number of candidates in the election, copies command-line arguments into the array
candidates, and asks the user to type in the number of voters. Then, the program lets every voter type in a vote (see how?), calling the
vote function on each candidate voted for. Finally,
main makes a call to the
print_winner function to print out the winner (or winners) of the election.
If you look further down in the file, though, you’ll notice that the
print_winner functions have been left blank. This part is up to you to complete!
Complete the implementation of
plurality.c in such a way that the program simulates a plurality vote election.
- Complete the
votetakes a single argument, a
name, representing the name of the candidate who was voted for.
namematches one of the names of the candidates in the election, then update that candidate’s vote total to account for the new vote. The
votefunction in this case should return
trueto indicate a successful ballot.
namedoes not match the name of any of the candidates in the election, no vote totals should change, and the
votefunction should return
falseto indicate an invalid ballot.
- You may assume that no two candidates will have the same name.
- Complete the
- The function should print out the name of the candidate who received the most votes in the election, and then print a newline.
- It is possible that the election could end in a tie if multiple candidates each have the maximum number of votes. In that case, you should output the names of each of the winning candidates, each on a separate line.
You should not modify anything else in
plurality.c other than the implementations of the
print_winner functions (and the inclusion of additional header files, if you’d like).
Your program should behave per the examples below.
$ ./plurality Alice Bob Number of voters: 3 Vote: Alice Vote: Bob Vote: Alice Alice
$ ./plurality Alice Bob Number of voters: 3 Vote: Alice Vote: Charlie Invalid vote. Vote: Alice Alice
$ ./plurality Alice Bob Charlie Number of voters: 5 Vote: Alice Vote: Charlie Vote: Bob Vote: Bob Vote: Alice Alice Bob
Be sure to test your code to make sure it handles…
- An election with any number of candidate (up to the
- Voting for a candidate by name
- Invalid votes for candidates who are not on the ballot
- Printing the winner of the election if there is only one
- Printing the winner of the election if there are multiple winners
Execute the below to evaluate the correctness of your code using
check50. But be sure to compile and test it yourself as well!
Execute the below to evaluate the style of your code using
How to Submit
- Download your
plurality.cfile by control-clicking or right-clicking on the file in CS50 IDE’s file browser and choosing Download.
- Go to CS50’s Gradescope page.
- Click “Problem Set 3: Plurality”.
- Drag and drop your
plurality.cfile to the area that says “Drag & Drop”. Be sure it has the correct filename, or the autograder will fail to run on it, and it will score no correctness points!
- Click “Upload”.
You should see a message that says “Problem Set 3: Plurality submitted successfully!” You won’t see a score just yet, but if you see the message then we’ve received your submission!