std::stack compilation error

Hi,

 I have the following program,

void dfs(struct node * root)
{
 if(root == NULL) return;
 std::stack <struct node *> s;
 s.push(root);

 while(!s.empty())
 {
  struct node * temp = s.pop();
  printf("%d ",temp->data);
  s.push(temp->rptr);
  s.push(temp->lptr);
 }
}

and i get a error saying,

 ro.c: In function `void dfs(node*)':
ro.c:419: `stack' undeclared in namespace `std'

Am i missing something?

Thanks in advance ! ! !