CS50 Runoff Pset3

runoff.c

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

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

// preferences[i][j] is jth preference for voter i(2d array)
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
//passed i,j and name of the candidate the user entered, look at line 77
bool vote(int voter, int rank, string name)
{
    bool exist = false;
    for (int i = 0; i < candidate_count; i++)
    {
        //check if name is present in the candidates entered by the user by camparing two strings 
        //strcmp is checking for the name and camparing it to the candidates array location 'i' which starts according to the for loop above 
        if (strcmp(name, candidates[i].name) == 0)
        {
            //if you found the person is present then add that number as a rank of the candidate in the preferences array
            //suppose this is a 2d array and the preference array is adding the preference number on a specific poistion so 
            // here ex - preferences[0][0] = i (the rank preferences from the candidate count) 
            // [i][][][]
            // [][][][]
            // [][][][]
            // [][][][]
            preferences[voter][rank] = i;
            exist = true;
            break;
            //This is a bool conditions which will become true, again look at line 77 
        }
    }
    return exist;
}

// Tabulate votes for non-eliminated candidates
void tabulate(void)
{
    // TODO
    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 += 1;
                break;
            }
        }
        
    }

    return;
}

// Print the winner of the election, if there is one
bool print_winner(void)
{
    // TODO
    for (int i = 0; i < candidate_count; i++)
    {
        string most = candidates[i].name;
        if (candidates[i].votes > voter_count / 2)
        {
            printf("%s\n", most);
            return true;
        }
    }
    return false;
}

// Return the minimum number of votes any remaining candidate has
int find_min(void)
{
    int minvotes = voter_count;
    for (int i = 0; i < candidate_count; i++)
    {
        if (candidates[i].eliminated == false && candidates[i].votes < minvotes)
        {
            minvotes = candidates[i].votes;
        }
    }
    return minvotes;
}

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

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

candidates[preferences[i][j]].votes
Can someone explain how these two things got combined? I thought preferences array was separate, and not totally understanding how we can just put it into the candidate struct variable. I am very new to any kind of programming, and wasn't sure what to even google to find this answer.
Also, if anyone has a good site they can recommend for some of the basic functions/rules of C.

I remember being very confused as well with programming, but it will definitely get better :).
Now, for your question. With candidates[preferences[i][j]].votes, you are indicating the number of votes the candidates has, in each voters preference.
Let me implement this more graphically!
So, when implementing the below function:

void tabulate(void)
{
// TODO
for (int i = 0; i < voter_count; i++)
{
for (int j = 0; j < candidate_count; j++)
{
if (candidates[preferences[i][j]].eliminated == false) \ if your candidate's elimination status in voters [i][j] is FALSE, thus not eliminated, do the below
{
candidates[preferences[i][j]].votes += 1; \ this just increments the above candidates votes by 1.
break;
}
}

}
return;

}

Now, candidates[preference[i][j]].votes indicates the amount of votes each candidate has in each voters preference array.
I hope I explained that clearly, but if you have any questions, please, please, please DO NOT hesitate to add another reply. @tara8970

Won't that make you add votes for all the [voters,candidates] array not only [voters,0] in the first iteration?

i'm getting this when making runoff

runoff.c:78:20: error: implicit declaration of function 'print_winnner' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
bool won = print_winnner();

why you include #include <stdbool.h> & #include <math.h>????

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I really appreciate your work man, you are helping students to solve mind-boggling problem sets. And your explanation is very easy to understand.
but, there is only one thing I am facing a problem with, I took references from many other answers as well but the same issues I am having. I am unable to visualize the pseudo code for the is_tie function, I mean, I can't able to visualize what it is doing. Can you elaborate on the pseudo-code for it?
When it will give true or when false.
It will be very helpful.

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thanks for your work on this mind-boggling problem! Can someone explain why is_tie works though? I really could not understand your reasoning behind this function :/

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Check CS50 is giving me this response:
:( print_winner prints name when someone has a majority
print_winner did not print winner of election
:( print_winner returns true when someone has a majority
print_winner did not print winner and then return true
:( print_winner returns false when nobody has a majority
print_winner did not return false
:( print_winner returns false when leader has exactly 50% of vote
print_winner did not return false

and this is my print_winner function:

bool print_winner(void)
{
for ( int i = 0; i < candidate_count; i++ )
{
if (candidates[i].votes > (candidate_count / 2))
{
printf("%s\n", candidates[i].name);
return true;
}
}

return false;

}

I am not able to understand where the problem is, if anybody can point it out for me it'll be a huge help.
Thanks in advance for your help

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please help me because as I run this code it is not compiling properly instead after entering one rank is giving the output of invalid .

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