C++ list empty()

#include <iostream>
#include <list>
using namespace std;
int main()/*from w  w w  .j ava2s . co m*/
{
   int j;
   list<int> list1, list2;
   int arr1[] = { 40, 30, 20, 10 };
   int arr2[] = { 15, 20, 25, 30, 35 };
   for(j=0; j<4; j++)
      list1.push_back( arr1[j] );    // list1: 40, 30, 20, 10
   for(j=0; j<5; j++)
      list2.push_back( arr2[j] );    // list2: 15, 20, 25, 30, 35
   list1.reverse();                  // reverse list1: 10 20 30 40
   list1.merge(list2);               // merge list2 into list1
   list1.unique();                   // remove duplicate 20 and 30
   int size = list1.size();
   while( !list1.empty() )
   {
      cout << list1.front() << ' ';  // read item from front
      list1.pop_front();             // pop item off front
   }
   cout << endl;
   return 0;
}