sort a pair using c++ stl

// C++ program to demonstrate sorting in vector 
// of pair according to 2nd element of pair 
#include<bits/stdc++.h> 
using namespace std; 
  
// Driver function to sort the vector elements 
// by second element of pairs 
bool sortbysec(const pair<int,int> &a, 
              const pair<int,int> &b) 
{ 
    return (a.second < b.second); 
} 
  
int main() 
{ 
    // declaring vector of pairs 
    vector< pair <int, int> > vect; 
  
    // Initialising 1st and 2nd element of pairs 
    // with array values 
    int arr[] = {10, 20, 5, 40 }; 
    int arr1[] = {30, 60, 20, 50}; 
    int n = sizeof(arr)/sizeof(arr[0]); 
  
    // Entering values in vector of pairs 
    for (int i=0; i<n; i++) 
        vect.push_back( make_pair(arr[i],arr1[i]) ); 
  
    // Printing the original vector(before sort()) 
    cout << "The vector before sort operation is:\n" ; 
    for (int i=0; i<n; i++) 
    { 
        // "first" and "second" are used to access 
        // 1st and 2nd element of pair respectively 
        cout << vect[i].first << " "
             << vect[i].second << endl; 
  
    } 
  
    // Using sort() function to sort by 2nd element 
    // of pair 
    sort(vect.begin(), vect.end(), sortbysec); 
  
    // Printing the sorted vector(after using sort()) 
    cout << "The vector after sort operation is:\n" ; 
    for (int i=0; i<n; i++) 
    { 
        // "first" and "second" are used to access 
        // 1st and 2nd element of pair respectively 
        cout << vect[i].first << " "
             << vect[i].second << endl; 
    } 
    return 0; 
}