Code:#include <iostream> #include <vector> #include <set> using namespace std; void add123(vector<set<int> >& numbers); int main() { vector<set<int> > vector_set; add123(vector_set); //cout << vector_set[0]; //how to print/access the 1st element of the first set of the vector vector_set? return 0; } void add123(vector<set<int> >& numbers) { set<int> s; s.insert(123); numbers.push_back(s); }