Plurality

Implement a program that runs a plurality election, as shown below.

$ ./plurality Alice Bob Charlie
Number of voters: 4
Vote: Alice
Vote: Bob
Vote: Charlie
Vote: Alice
Alice

Background

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.

Getting Started

Here’s how to download this problem’s “distribution code” (i.e., starter code) into your own IDE. In the terminal window, execute the following command:

wget https://scienceacademy.github.io/web/plurality.c

Understanding

Now take a look at plurality.c and read through the distribution code that’s been provided to you.

The line #define MAX 9 is C syntax - used here to mean that MAX is a constant (equal to 9) that can be used throughout the program. It represents the maximum number of candidates an election can have.

The file then defines a struct called candidate. Each candidate has two fields: a string called name representing the candidate’s name, and an int called votes representing the number of votes the candidate has. Next, the file defines a global array of candidates, where each element is itself a candidate.

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, 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, you’ll notice that the vote() and print_winner() functions have been left blank. This part is up to you to complete!

Specification

Complete the implementation of plurality.c so that the program simulates a plurality vote election.

• Complete the vote function.
  • vote() takes a single argument, a string called name, representing the name of the candidate who was voted for.
  • If name matches one of the names of the candidates in the election, then update that candidate’s vote total to account for the new vote. The vote() function in this case should return true to indicate a successful ballot.
  • If name does not match the name of any of the candidates in the election, no vote totals should change, and the vote() function should return false to indicate an invalid ballot.
  • You may assume that no two candidates will have the same name.
• Complete the print_winner() function.
  • 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 vote() and print_winner() functions (and the inclusion of additional header files, if you’d like).

Usage

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

Testing

Be sure to test your code to make sure it handles the following:

• An election with any number of candidates (up to the MAX)
• Voting for a candidate by name
• Invalid votes for candidates who are not on the ballot
• Printing the winner of the election if there’s only one
• Printing the winners of the election if there are multiple winners

Execute the below to test the correctness of your code using check50. Be sure to compile and test it yourself!

check50 scienceacademy/problems/2024ap/plurality

How to Submit

Execute the below to submit your code:

submit50 scienceacademy/problems/2024ap/plurality