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);
}