#include <iostream>
#include <vector>
using namespace std;
void add_number(vector<int> &vec) {
vec.push_back(4);
}
int main()
{
vector<int> vec;
vec.push_back(1);
vec.push_back(2);
vec.push_back(3);
add_number(vec);
for(auto const& v : vec) cout << v << " ";
return 0;
}
/*
run:
1 2 3 4
*/