BFS on Adjacency Matrix

Question

I'm trying to implement a BFS on adjacency matrix of undirected unweighted graph which returns the number of nodes visited. I've come up with this till now but I think this is not right as when I print out the top/ visited node, I'm getting multiple occurrences of some nodes as well as it's not sorted. I've read somewhere that BFS is a topological sort and the order I get is not sorted.

int BFS(std::vector<std::vector<int> > &matrix, int start)
{
    std::vector<bool> visited(matrix.size(), false);
    std::queue<int> Q;
    Q.push(start);
    int count = 0;

    while( ! Q.empty())
    {
        int top = Q.front(); Q.pop();
        visited[top] = true; count++;
        for (int i = 0; i < matrix.size(); ++i)
        {
            if(matrix[top][i] != 0 && (! visited[i]) )
            {
                Q.push(i);
            }
        }
    }
    return count;
}

Answer 1

Instead of setting visited node to true after popping the queue, you should set it when you insert it to the queue, and add count inside as well, as to prevent double counting of some nodes. Please refer to the following:

//..previous lines

Q.push(start);
visited[start] = true;
int count = 1;

while(!Q.empty()){
    int top = Q.front(); Q.pop();

    for (int i = 0; i < matrix.size(); ++i){
        if(matrix[top][i] != 0 && (! visited[i]) ){
            Q.push(i);
            visited[i] = true;
            count++;
        }
    }
}