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Having issues with Check 50 and the is_tie function:

:( is_tie returns false when only some of the candidates are tied
    is_tie did not return false
:( is_tie detects tie after some candidates have been eliminated
    is_tie did not return true

I get these errors within Check50 but i am unsure why. See my code below.

bool is_tie(int min)
{
    //Create a variable that stores the amount of Candidates still in the race.
    int remaining_candidates = 0;

    //Loop over the candidates and find out how many candidates still are standing.
    for (int i = 0; i < candidate_count; i++)
    {
        if (candidates[i].eliminated == false)
        {
            remaining_candidates++;
        }

    }

    //Loop over the candidates a second time now to test the equation and see if a tie exists
    for (int j =0; j < candidate_count; j++)
    {
        if ((voter_count / candidates[j].votes) == remaining_candidates)
        {
            printf("\nIts a Tie\n");
            return true;
        }

        else
        {
            return false;
        }
    }
    return false;
}

I understand the faults to be saying that my function returns "true" when only some candidates are tied. but I thought I had eliminated this from possibly happening in the "find-min" function and the "eliminate" function as invalid candidates would be either eliminated or ignored in this function.

if anyone could give me some insight I would most appreciate it. full source code below:

#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 (i being rows and j being columns)
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("Voter %i - Rank %i: ", i + 1, 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();

        for (int j = 0; j < candidate_count; j++)
    {
        printf("candidate: %s\n votes:%d\n", candidates[j].name, candidates[j].votes);
    }

        // 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("Joint Victor %i: %s\n",(i+1), 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)
{
    // Iterate over the number of candidates
        for(int i = 0; i < candidate_count; i++)
        {

            //Check if any of the name entered by the user matches any of the candidates names
            if (strcmp(name, candidates[i].name) == 0)
            {
                preferences[voter][rank] = i;
                return true;
                break;
            }
        }

    return false;
}

// Tabulate votes for non-eliminated candidates
void tabulate(void)
{
    // Iterate over the number of candidates to find 'true' votes

    for(int i = 0; i < voter_count; i++)
    {

        for (int j = 0; j < candidate_count; j++)
        {

            if (candidates[preferences[i][j]].eliminated == false)
            {
                candidates[preferences[i][j]].votes++;
                break;
            }
        }
    }

    return;
}

// Print the winner of the election, if there is one
bool print_winner(void)
{
    for (int i = 0; i < candidate_count; i++)
    {

        if (candidates[i].votes > (voter_count/2))
        {
            printf("\nElection winner: %s\n", candidates[i].name);
            return true;
        }

    }
    return false;
}

// Return the minimum number of votes any remaining candidate has
int find_min(void)
{
    int losing_candidates_count = voter_count;
    string losing_candidate;

    for (int i = 0; i < candidate_count; i++)
    {
        if (candidates[i].votes < losing_candidates_count && candidates[i].eliminated == false)
        {
            losing_candidates_count = candidates[i].votes;
        }
    }

    printf("\n Lowest ranking candidate:  ");

    for (int i = 0; i < candidate_count; i++)
    {
        if (candidates[i].votes == losing_candidates_count && candidates[i].eliminated == false)
        {
            losing_candidate = candidates[i].name;
        }
    }

    printf(" %s\n", losing_candidate);

    return losing_candidates_count;
}

// Return true if the election is tied between all candidates, false otherwise
bool is_tie(int min)
{
    //Create a variable that stores the amount of Candidates still in the race.
    int remaining_candidates = 0;

    //Loop over the candidates and find out how many candidates still are standing.
    for (int i = 0; i < candidate_count; i++)
    {
        if (candidates[i].eliminated == false)
        {
            remaining_candidates++;
        }

    }

    //Loop over the candidates a second time now to test the equation and see if a tie exists
    for (int j =0; j < candidate_count; j++)
    {
        if ((voter_count / candidates[j].votes) == remaining_candidates)
        {
            printf("\nIts a Tie\n");
            return true;
        }

        else
        {
            return false;
        }
    }
    return false;
}

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

    return;
}

3
  • I do not understand the approach used here viz. if ((voter_count / candidates[j].votes) == remaining_candidates). A tie means all remaining candidates have the same number of votes. It is not a function of how many candidates are remaining, it is a simply a comparison of the number of votes each remaining candidate has accumulated. Feb 4 at 16:17
  • Thanks for your comment mate.
    – Pot Noodle
    Feb 4 at 17:25
  • Thanks for your comment mate. my logic was that the programme is incapable of instinctively seeing all the votes are the same so i need to sum up all the information already gathered in the arrays into 2 figures for comparison. or use the numerical figures to find a mathmatical relationship to derive a tie situation... so if e.g 6 voters (voter count) / e.g. 3 candidates vote count (candidates[j].votes) = e.g 2 standing candidates (remaining_candidates) then a tie exists.
    – Pot Noodle
    Feb 4 at 17:32
1

This for (int j =0; j < candidate_count; j++) only ever tests the 1st candidate, because it returns from the if/else block. (And it doesn't care whether candidate has been eliminated!).

This election will produce an invalid result: 4 candidates (a b c d), 8 voters whose first choices are a, a, b, b, b, b, c, d respectively. The rest of the ballot doesn't matter because function will report a tie on the first iteration when it processes candidate[0] (a).

Remember: is_tie is called before eliminate.

1
  • AWESOME! thank you so much mate. i thought this was what was wrong but I was conviced that the previous functions worked as a failsafe. Thanks mate, I really appreciate your help..... back to the drawing board haha
    – Pot Noodle
    Feb 4 at 22:24

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