Bidirectional Iterator

#include <iostream>
#include <string>
#include <list>
 
using namespace std;
 
int main()
{
  list<int> lst1(8);
 
  cout <<"\nFirst we enter some integer squares into "
         "a list of size 8, and then display: \n";
  //Create and initialize an iterator.
  list<int>::iterator p = lst1.begin();
  int i = 0;
 
  while(p != lst1.end())
  {
    *p = i*i; //Assign i*i to list lst via iterator p.
    p++;      //Advance the iterator **after** using it.
    i++;      //Increment the value to be squared.
  }
  p = lst1.begin();
  while(p != lst1.end()) 
    cout <<*p++<<" ";
 
  cout <<"\nNext we double the values in the list and "
         "re-display (backwards this time): \n";
  p = lst1.begin();
  while(p != lst1.end())
  {
    *p = *p * 2;
    p++;
  }
  //This time, initialize the iterator to lst1.end().
  //And decrement the iterator **before** using it!
   p = lst1.end();
   while(p != lst1.begin())
     cout <<*--p<<" "; //Note *--p "idiom".
 
  return 0;
}