If you want to reverse the order of elements in a given range, then you can use the reverse function defined in the STL algorithm.

Template for reverse

template <class BidirectionalIterator>
  void reverse (BidirectionalIterator first, BidirectionalIterator last);

About parameters
InputIterator first
InputIterator first for the initial position of the range which is included in the range.
InputIterator last
InputIterator last for the final position which it not included in the range.

A sample program using reverse

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

using namespace std;

int main()
{
        vector <int> v;
        vector <int>:: iterator it;

        // Pushing 11 random elements inside the vector
        v.push_back(11);
        v.push_back(10);
        v.push_back(9);
        v.push_back(8);
        v.push_back(7);
        v.push_back(6);
        v.push_back(5);
        v.push_back(4);
        v.push_back(3);
        v.push_back(2);
        v.push_back(1);

        // printing the elemnets inside the raange
        cout <<"Elements inside the range. " << endl;
        for ( it = v.begin(); it != v.end(); it++)
                cout << *it << " ";
        cout << endl;

        //applying reverse function on the range
        reverse(v.begin(),v.end());

        // printing the elemnets inside the range
        cout <<"Elements inside the range after reverse. " << endl;
        for ( it = v.begin(); it != v.end(); it++)
                cout << *it << " ";
        cout << endl;

        return 0;
}

Output of the above program

Elements inside the range. 
11 10 9 8 7 6 5 4 3 2 1 
Elements inside the range after reverse. 
1 2 3 4 5 6 7 8 9 10 11

Time complexity for reverse is linear in half the distance between the range.