Build error

#include <iostream>
#include <vector>
#include <string>

using std::cout;
using std::endl;
using std::vector;
using std::string;

template <class T>
void print_size_and_contents(T v, string vn) {
  cout << "Size of " << vn << " " << v.size() << endl;
  cout << "Contents:";
  for (decltype(v.size()) i : v)
    cout << i << endl;
}

int main(void) {
  vector<int> v1;
  vector<int> v2(10);
  vector<int> v3(10, 42);
  vector<int> v4{10};
  vector<int> v5{10,42};
  vector<string> v6{10};
  vector<string> v7{10,"hi"};

  print_size_and_contents(v1, "v1");
  print_size_and_contents(v2, "v2");
  print_size_and_contents(v3, "v3");
  print_size_and_contents(v4, "v4");
  print_size_and_contents(v5, "v5");
  print_size_and_contents  (v6, "v6");
  print_size_and_contents  (v7, "v7");


  return 0;
}