Dmitry

#include <algorithm>
#include <iterator>
#include <iostream>
#include <vector>

using namespace std;

auto fx = [](int x){
  int r = 0;
  switch(x % 3)
  {
    case 0:
      r = x * x;
      break;
    case 1:
      r = x;
      break;
    default:
      r = x / 3;
      break;
  }
  return r;
};

auto calculate = [](const vector<int>& vx, auto fx){
  vector<int> calcValues(vx.size());
  transform(vx.begin(), vx.end(), calcValues.begin(), fx);
  return calcValues;
};

int main()
{
  cout << "Введи кол-во чисел: ";
  int n = 0;
  cin >> n;

  cout << "Введи через пробел " << n << " натуральных чисел:\n" << "$: ";
  vector<int> values(n);
  copy_n(istream_iterator<int>(cin), n, values.begin());

  cout << "Результат твоих расчетов:\n";
  copy_n(calculate(values, fx).begin(), n, ostream_iterator<int>(cout, "\n"));
}

#include <iostream>
#include <sstream>
#include <algorithm>
#include <iterator>
#include <vector>
using namespace std;

int main()
{
  size_t n = 4;
  string s = "42 54 35 76";
  
  istringstream is(s);
  
  vector<int> v;
  copy_n(istream_iterator<int>(is), n, back_inserter(v));

  /*******
  ** vector<int> v2(n);
  ** copy_n(istream_iterator<int>(is), n, v.begin());
  *******/
  copy_n(v.begin(), n, ostream_iterator<int>(cout, " "));
}