C + + seeking FIB sequence _c language

1. The first version of the program

int fib (int pos)
  {
    int elem = 1;
    int n1 = 1, N2 = 1;
    for (int i = 3; I <= pos; i++)
    {
      Elem = n2 + n1;
      N1 = n2;
      N2 = Elem;
    }
    return elem;
  }

2. The second version

BOOL Fib (int pos, int &elem)
  {
    if (pos < 0 | | pos > 1024)
    {
      elem = 0;
      return false;
    }
    Elem = 1; Note: The definition can only be 1 times
    int n1 = 1, N2 = 1;
    for (int i = 3; I <= pos; i++)
    {
      Elem = n2 + n1;
      N1 = n2;
      N2 = Elem;
    }
    return true;
  }

Main function call

int main ()
  {  
      int pos;
    cout << "Please enter a position:";
    CIN >> POS;
  
    int elem;
    if (FIB (POS, elem))
    {
      cout << "element #" << Pos
         << "is" << elem << endl;
   
    
    else
      cout << Sorry. Couldn ' t calculate element #
         << pos <<endl;
  }

   

3. Third version of the improved FIB

Const vector<int>* fib_new (int size)
  {
    const int max_size = 1024;
    Static vector<int> Elems;
  
    if (size <= 0 | |-size >= max_size)
    {
      cerr << "Fib_new (): Oops:invalid size:"
         << size << "-Can ' t fulfill request.\n";
      return 0;
    }
    for (int ix = Elems.size (); ix < size; ix++)
    {
      if (ix = 0 | | | ix = 1)
        elems.push_back (1);
      else
        Elems.push_back (elems[ix-1] + elems[ix-2]);
    }
    Return &elems;
  }

Main function call

    Const vector<int> *result=fib_new (5);
    cout << result->back ();
    
    Const vector<int> *result=fib_new (5);
    cout << Result->at (4) << Endl;
    How many times this should be called back, this is not clear, leave a mark.

This last version avoids repeated operations and uses a local static object.