Swap second and fourth element in a vector

/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <iterator>
using namespace std;

int main()
{
// create empty vector for strings
vector<string> sentence;

// reserve memory for five elements to avoid reallocation
sentence.reserve(5);

// append some elements
sentence.push_back("Hello,");
sentence.push_back("how");
sentence.push_back("are");
sentence.push_back("you");
sentence.push_back("?");

// swap second and fourth element
swap (sentence[1], sentence[3]);
// print elements separated with spaces
copy (sentence.begin(), sentence.end(),
ostream_iterator<string>(cout," "));
cout << endl;

}