// program that sets up a reference to the first value in a vector,
// but the vector is resized when a value is added to it, making this
// a reference to an unused part of memory

#include <iostream>
#include <vector>

using namespace std;
        
int main() {
    vector<int> v{10, 20,};
    int & x = v[0];
    v.push_back(30);
    x++;
    cout << x << endl;

    return 0;
}