pset3 plurality - candidates votes are not being updated - CS50

Question

I trying to finish pset3 for CS50, plurality and my code does not update the votes for each candidate. I have implemented the vote function, but it seems not to work. Do you know where I need to improve my code?

This is my code at the moment:

#include <cs50.h>
#include <stdio.h>
#include <string.h>

// Max number of candidates
#define MAX 9

// Candidates have name and vote count
typedef struct
{
    string name;
    int votes;
}
candidate;

// Array of candidates
candidate candidates[MAX];

// Number of candidates
int candidate_count;

// Function prototypes
bool vote(string name);
void print_winner(void);

int main(int argc, string argv[])
{
    // Check for invalid usage
    if (argc < 2)
    {
        printf("Usage: plurality [candidate ...]\n");
        return 1;
    }

    // Populate array of candidates
    candidate_count = argc - 1;
    if (candidate_count > MAX)
    {
        printf("Maximum number of candidates is %i\n", MAX);
        return 2;
    }
    for (int i = 0; i < candidate_count; i++)
    {
        candidates[i].name = argv[i + 1];
        candidates[i].votes = 0;
    }

    int voter_count = get_int("Number of voters: ");

    // Loop over all voters
    for (int i = 0; i < voter_count; i++)
    {
        string name = get_string("Vote: ");

        // Check for invalid vote
        if (!vote(name))
        {
            printf("Invalid vote.\n");
        }
    }

    // Display winner of election
    print_winner();
}

// Update vote totals given a new vote
bool vote(string name)
{
    // TODO
    for (int i = 0; i < candidate_count; i++)
    {
        if (strcmp(candidates[i].name, name) == 0)
        {
            candidates[i].votes++ ;
            return true;
        }
    }
    return false;
}

// Print the winner (or winners) of the election
void print_winner(void)
{
    // TODO
    int highest_vote = 0;
    string winner;
    for (int i = 0; i < candidate_count; i++)
    {
        if (candidates[i].votes >= candidates[0].votes)
        {
            highest_vote = candidates[i].votes;
            winner = candidates[i].name;
        }
    }
    printf("%s\n", winner);
    return;
}

INPUT:

./plurality a b c d
Number of voters: 5
Vote: a
Vote: a
Vote: b
Vote: b
Vote: c

OUTPUT:

b

I have used debug50 to see where the problem lies, but I could not get to the solution. Has anyone also done pset3 and has any helpful ideas?

Answer 1

Your problem is here:

bool vote(string name)
{
    // TODO
    // LOOK OUT HERE FOR THE MISTAKE
    for (int i = 0; i < candidate_count; i++)
    {
        if (strcmp(candidates[i].name, name) == 0)
        {
            candidates[i].votes++ ;
            return true;
        }
        return false;  // <<<<<<<<<<<<<<<<<< ERROR!
    }
}

If you don't find a match during first iteration, you return from the function and bob never gets a change to count some votes. You need to move the second return after the loop.

bool vote(string name)
{
    for (int i = 0; i < candidate_count; i++)
    {
        if (strcmp(candidates[i].name, name) == 0)
        {
            candidates[i].votes++;
            return true;
        }
    }
    return false;
}

And another problem:

   for (int i = 1; i <= candidate_count; i++)
    {
        if (candidates[i].votes > highest_vote)
        {
            candidates[i].votes = highest_vote;
        }
    }

First of all: The index should start at 0 as mentioned in my comment. Second: You must update highest_vote , not the other way around.

    for (int i = 0; i < candidate_count; i++)
    {
        if (candidates[i].votes > highest_vote)
        {
            highest_vote = candidates[i].votes;
        }
    }

Answer 2

Your vote function seems to be fine. Print_winner, not so much. Some redundancy, some weird stuff. Try to keep it simple. I see you already solved it, but might help to compare where you used stuff/lines you didn't need.

void print_winner(void)
{
    int winner = 0;
    // The var 'winner' is an int, a number of votes, not a name.

    // Finding the highest number of votes
    for (int i = 0; i < candidate_count; i++)
    {
    if (candidates[i].votes > winner)
        {
            winner = candidates[i].votes;
        }
    }

    // Printing the names of all candidates with 'winner' number of votes
    for (int j = 0; j < candidate_count; j++)
    {
        if (candidates[j].votes == winner)
        {
            printf("%s\n", candidates[j].name);
        }
    }
    return;
}