cfunctioncs50vote

Vote function in Tideman (pset 3 of CS50)

I'm trying to deal with the vote function and there are 2 questions I'd like to seek for your help:

  1. In the vote function definition, we have:
bool vote(int rank, string name, int ranks[])

I don't understand what the rank parameter is for and why is it declared here?

  1. My solution for the vote function as follows:
// Update ranks given a new vote
bool vote(int rank, string name, int ranks[])
{
    for (int j = 0; j < candidate_count; j++)
    {
        for (int k = 0; k < candidate_count; k++)
        {
            //Compare the name provided by the user with the name of the candidates numbered jth in the array candidates[MAX] which already populated above
            if (strcmp(name, candidates[k]) == 0)
            {
                ranks[j] = k;
                printf("ranks[%d] = %d\n", j, k);
                }
        }
        return true;
    }
    return false;
}

The result of the printf function as follows (with candidates = {a,b,c}, voter_count = 2):

Rank 1: a, ranks[0] = 0; Rank 2: b, ranks[0] = 1; Rank 3: c, ranks[0] = 2; Rank 1: c, ranks[0] = 2; Rank 2: b, ranks[0] = 1; Rank 3: a, ranks[0] = 0

The value of j in ranks[j] was not updated. How can I resolve this problem?

Thanks so much for your help!

Solution

  • Here is some code:

    // Update ranks given a new vote    
bool vote(int rank, string name, int ranks[]){                      
    
    //We want to cycle through the list of candidates given
    for(int i = 0; i < candidate_count; i++){

        //If the candidate(s) in the array matches with string name, we will continue
        if(strcmp(candidates[i], name) == 0){

            //This is the tricky part to understand. Read below for answer.
            ranks[rank] = i;
            return true;
        }
    }
    
    return false;
}

    int rank represents the user's given rank for the candidate and int i would the candidate's position in the candidates[]. We want to update the ranks[] according to the right rank. This is still quite confusing to understand so here is an example.

    We have four candidates: John, Jim, Sam, Alex

    In string candidates[MAX];, John is at candidates[0], Jim is at candidates[1], Sam is at candidates[2], and Alex is at candidates[3].

    Suppose the user gives their vote and they vote in this order:

    1. Alex
    2. John
    3. Jim
    4. Sam

    Let's run it in the bool vote(int rank, string name, int ranks[]).

    1. vote(j, name, ranks) where j = 0, name = Alex, and ranks is the ranks[]
    2. We will loop the name Alex until we find it in candidates[MAX].
    3. Alex is found in candidates[i] where i = 3.
    4. We want to update the ranks[]
    5. ranks[rank] = i; would mean that at ranks[rank] is equal to i which is 3. In other words, ranks[0] is equal to Alex's ith position in the candidates[MAX].

    Then you repeat this cycle until all the voter's ranking is done.