#include <iostream>
#include <vector>
using namespace std;

int main() {
    vector<int> v; //only int type

    v.push_back(1);
    v.push_back(2);
    v.push_back(3);

    for(int i=0; i<v.size(); i++)
        cout<<v[i]<<" ";          //1 2 3
    cout<<endl;

    v[0] = 9;
    int n = v[2];
    v.at(2) = 7;

    for(int i=0; i<v.size(); i++)
        cout<<v[i]<<" ";
    cout<<endl;                  //9 2 7
}