ex3_20.cpp

#include <iostream>
#include <vector>

using std::vector; using std::cout; using std::endl; using std::cin;

int main()
{
  vector<int> ivec;
  int i;
  while (cin >> i)
    ivec.push_back(i);  
  
  if (ivec.empty())
  {
    cout << "input at least one integer." << endl;
    return -1;
  }
  else if (ivec.size() == 1)
  {
    cout << ivec[0] << " don't have any adjacent elements.";
  }
  else
  {
    for(decltype(ivec.size()) i=0; i!=ivec.size()-1; ++i)
    cout << ivec[i] + ivec[i+1] << " ";
  }

  cout << endl;

  decltype(ivec.size()) size = ivec.size();
  if (size%2 != 0) size = size/2 + 1;
  else size /= 2;

  for(decltype(ivec.size()) i = 0; i != size; ++i)
    cout << ivec[i] + ivec[ivec.size()-i-1] << " ";
  cout << endl;  

  return 0;
}