Nrthugu

I'm trying to implement what I've learned about std::vector to solve a problem. User is going to input a list of animal names (not specified how many) and I need to record the animal names and their occurrences in the user input. At first, I tried using an array, but as it's static, I turned to std::vector. Again, at first, I tried using two std::vector, one with type int and the other with type string to store the animal names and the amount of occurrences. However, it seems a bit hard to sort both vectors later and a std::vector with a pair type sounds better in my mind. And now, I'm stuck with this code below with errors I don't quite understand:

#include <bits/stdc++.h>

#include <sstream>



using namespace std;



int position(vector< pair<string, int> > myList, string animalName) {

    int pos;

    for (int i = 0; i < myList.size(); i++) if (animalName.compare(myList[i].first) == 0) pos = i;

    return pos;

}



int main() {

    int Q;

    cin >> Q;



    vector< pair<string, int> > zooPair;

    string animal;



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

        cin >> animal;

        if (find_if(zooPair.begin(), zooPair.end(), animal.compare(zooPair.first) == 0) == zooPair.end())

            zooPair.emplace_back(animal, 1);

        else

            zooPair[position(zooPair, animal)].second += 1;

    }



    sort(zooPair.begin(), zooPair.end());



    for (vector< pair<string, int> >::iterator it = zooList.begin(); it != zooList.end(); it++)

        cout << *it;



    return 0;

}

You simply should use std::map as the container type, because it already sorts, have a easy to use access interface with operator. Here we create a std::map with your animal and the number of them in your zoo.

Example:

int main() {

    int Q;

    std::cout << "Enter number of entries" << std::endl;

    std::cin >> Q;



    std::map<std::string, int> zoo;



    std::string animal;



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

        std::cout << "Enter animal" << std::endl;

        std::cin >> animal;

        zoo[animal]++;

    }



    for ( auto& it: zoo )

    {

        std::cout << it.first << " " << it.second << std::endl;

    }





    return 0; 

}

As you see, there is no need for an additional sort as a map is always sorted for the first part, named the "key", of every entry.

The same with std::vector. Remark that you have to give operators for sort and find!

Full example:

struct SortableElements: public std::pair< std::string, int >

{

    // forward construction 

    using std::pair<std::string, int>::pair;



    // use for sort: 

    bool operator < (const SortableElements& e2 ) const

    {

        return first < e2.first;

    }



    // use for find: 

    bool operator == ( const std::string& e2 ) const

    {

        return first == e2;

    }

};







int main() 

{   

    std::vector< SortableElements > zoo;



    int Q;

    std::cout << "Enter number of entries" << std::endl;

    std::cin >> Q;



    std::string animal;



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

        std::cout << "Enter animal" << std::endl;

        std::cin >> animal;



        auto it = std::find( zoo.begin(), zoo.end(), animal);

        if ( it != zoo.end())

        {

            it->second++;

        }

        else

        {

            zoo.emplace_back( animal, 1 );

        }

    }



    // sort:

    std::sort(zoo.begin(), zoo.end());



    for ( auto& it: zoo )

    {

        std::cout << it.first << " " << it.second << std::endl;

    }



    return 0;

}