cs50 pset3 runoff tabulate

Question

i have completed the problem set however when i check, this is the only problem.

:) tabulate counts votes when all candidates remain in election :) tabulate counts votes when one candidate is eliminated :( tabulate counts votes when multiple candidates are eliminated tabulate function did not produce correct vote totals

i have checked and cant seem to find the solution even through debugging?also i feel like the function is logical and does not contain issues i found in other related questions.

i have included all the code in case the issue does not lie with the tabulate function. thank you.

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

// Max voters and candidates
#define MAX_VOTERS 100
#define MAX_CANDIDATES 9

// preferences[i][j] is jth preference for voter i
int preferences[MAX_VOTERS][MAX_CANDIDATES];

// Candidates have name, vote count, eliminated status
typedef struct
{
    string name;
    int votes;
    bool eliminated;
}
candidate;

// Array of candidates
candidate candidates[MAX_CANDIDATES];

// Numbers of voters and candidates
int voter_count;
int candidate_count;

// Function prototypes
bool vote(int voter, int rank, string name);
void tabulate(void);
bool print_winner(void);
int find_min(void);
bool is_tie(int min);
void eliminate(int min);

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

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

    voter_count = get_int("Number of voters: ");
    if (voter_count > MAX_VOTERS)
    {
        printf("Maximum number of voters is %i\n", MAX_VOTERS);
        return 3;
    }

    // Keep querying for votes
    for (int i = 0; i < voter_count; i++)
    {

        // Query for each rank
        for (int j = 0; j < candidate_count; j++)
        {
            string name = get_string("Rank %i: ", j + 1);

            // Record vote, unless it's invalid
            if (!vote(i, j, name))
            {
                printf("Invalid vote.\n");
                return 4;
            }
        }

        printf("\n");
    }

    // Keep holding runoffs until winner exists
    while (true)
    {
        // Calculate votes given remaining candidates
        tabulate();

        // Check if election has been won
        bool won = print_winner();
        if (won)
        {
            break;
        }

        // Eliminate last-place candidates
        int min = find_min();
        bool tie = is_tie(min);

        // If tie, everyone wins
        if (tie)
        {
            for (int i = 0; i < candidate_count; i++)
            {
                if (!candidates[i].eliminated)
                {
                    printf("%s\n", candidates[i].name);
                }
            }
            break;
        }

        // Eliminate anyone with minimum number of votes
        eliminate(min);

        // Reset vote counts back to zero
        for (int i = 0; i < candidate_count; i++)
        {
            candidates[i].votes = 0;
        }
    }
    return 0;
}

// Record preference if vote is valid
bool vote(int voter, int rank, string name)
{
    for(int x = 0; x < candidate_count; x++)
    {
        if (strcmp(name,candidates[x].name) == 0)
        {
            preferences[voter][rank] = x;
            return true;
        }
    }
    return false;
}
// Tabulate votes for non-eliminated candidates        **here is the relevant code**
void tabulate(void)
{
    for (int v = 0; v < voter_count; v++)
    {
        for (int r = 0; r < candidate_count; v++)
        {
            if(candidates[preferences[v][r]].eliminated == false )
            {
                candidates[preferences[v][r]].votes++;
                break;
            }
        }
    }
    return;
}

// Print the winner of the election, if there is one
bool print_winner(void)
{
    for(int c = 0; c < candidate_count; c++)
    {
        if (candidates[c].votes > (voter_count * 0.5))
        {
            printf("%s\n",candidates[c].name);
            return true;
        }
    }
    return false;
}

// Return the minimum number of votes any remaining candidate has
int find_min(void)
{
    int min[1] = {0};
    for ( int c = 0; c < candidate_count; c++)
    {
        if (candidates[c].votes > min[0])
        {
            min[0] = candidates[c].votes;
        }
    }
    return min[0];
}

// Return true if the election is tied between all candidates, false otherwise
bool is_tie(int min)
{
    for (int c = 0; c< candidate_count; c++)
    {
        if (candidates[c].votes != min && candidates[c].eliminated == false)
        {
            return false;
        }
    }
    return true;
}

// Eliminate the candidate (or candidiates) in last place
void eliminate(int min)
{
    for (int c = 0; c < candidate_count; c++)
    {
        if (candidates[c].votes == min)
        {
            candidates[c].eliminated = true;
        }
    }
    return;
}

Answer 1

I think there a problem with this line of code:

        if(candidates[preferences[v][r]].eliminated == false )
        {
            candidates[preferences[v][r]].votes++;
            break;

What happens when it finds the first choice for a candidate has been eliminated? Because it needs to check what his next choice is and so forth. Until it ether finds a candidate that has not been eliminated or there is no more candidates.

Answer 2

How does this function returns the minimum votes and not the maximum votes?

int find_min(void)
{
    int min[1] = {0};
    for ( int c = 0; c < candidate_count; c++)
    {
        if (candidates[c].votes > min[0])
        {
            min[0] = candidates[c].votes;
        }
    }
    return min[0];
}

Answer 3

I was Encountering the same error and that was all due to a silly mistake we both have done. Have a Look here in the code

void tabulate(void)
{
    for (int v = 0; v < voter_count; v++)
    {
        for (int r = 0; r < candidate_count; v++)
        {
            if(candidates[preferences[v][r]].eliminated == false )
            {
                candidates[preferences[v][r]].votes++;
                break;
            }
        }
    }
    return;
}

Now have a closer look at this line only

for (int r = 0; r < candidate_count; v++)

You are Initialising r = 0;. But Incrementing v++; Just Replace that Vwith r and you are done.

Answer 4

I can find nothing wrong with your logic, and I did the exact same thing, have a look if this solves the problem. I just used different syntax and it works: (before we got into the loop, I initialized temp) int temp; . . . temp = preferences[v][r];

if (!candidates[temp].eliminated) { candidates[temp].votes++; break; }

I'm not sold on why this should work vis-a-vis what you did, but sometimes syntax does make a difference - and for some reason this works for me