Непонятно, как работает push_back

    vector<char> h; char q;
 
    q=')';
    h.push_back(q);
    if(h.empty()) printV(h); else cout<<"ERROR"<<endl;

    unsigned int N; vector<rate> Sigma;
 
    cin>>N;
    for(unsigned int i=1;i<=N;i++){
        string o;
 
        getline(cin,o);
        Sigma.push_back(make_pair(o,i));
    }

#include <iostream>
#include <string>
#include <vector>
 
struct rate
{
   std::string name;
   int rating;
 
   rate(const std::string& s, int r): name(s), rating(r) {}
};
 
int main()
{
   std::vector<rate> Sigma;
   std::string name;
   unsigned int N;
   (std::cin >> N).get();
   for(unsigned int i = 0; i<N; ++i)
   {
      std::cout << "Enter name: ";
      std::getline(std::cin, name);
      Sigma.push_back(rate(name, i));
   }
   for(std::vector<rate>::iterator it = Sigma.begin(); it != Sigma.end(); ++it)
      std::cout << (*it).name << ", " << (*it).rating << std::endl;
 
   std::cout << "\nDone" << std::endl;
   return 0;
}

#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
using namespace std;
 
typedef pair<string, unsigned int> rate;
 
void ShowMeStudents(vector<rate> &v){
    for(unsigned int a=0;a<v.size();a++){
        cout<<v[a].first<<" "<<"("<<v[a].second<<")"<<endl;
    }
    cout<<endl;
}
 
int main(){
    unsigned int N; vector<rate> Sigma; string o;
 
    cin>>N;
    for(unsigned int i=1;i<=N;i++){
        getline(cin,o);
        Sigma.push_back(rate(o,i));
    }
    sort(Sigma.begin(),Sigma.end());
    ShowMeStudents(Sigma);
    return 0;
}

pair<T1, T2>
 
template <class T1, class T2> struct pair
{
    T1 first;
    T2 second;
};

template<class T1, class T2> struct pair
{
T1 first;
T2 second;
 
pair(T1 f,T2 s) : first(f), second(s) {}
 
};

#include <iostream>
#include <string>
#include <vector>
 
typedef std::pair<std::string, unsigned int> rate;
 
void ShowMeStudents(const std::vector<rate>& v)
{
    for(unsigned int i = 0; i<v.size(); ++i){
        std::cout << v[i].first << " " << "(" << v[i].second << ")" << std::endl;
    }
    std::cout << std::endl;
}
 
int main()
{
   std::vector<rate> Sigma;
   std::string name;
   unsigned int N;
   (std::cin >> N).get();
   for(unsigned int i = 0; i<N; ++i)
   {
      std::cout << "Enter name: ";
      std::getline(std::cin, name);
      Sigma.push_back(std::make_pair(name, i));
   }
   ShowMeStudents(Sigma);
 
   std::cout << "\nDone" << std::endl;
   return 0;
}

std::sort(Sigma.begin(), Sigma.end(), [](const rate& r1, const rate& r2) 
{return r1.first < r2.first;});