Question

I am working with a link list. I have set my constructor to take an array named ax with a set of already defined items. I also decided to have an input box which through a BtnAddTree_Click appends the new item to the list ax. But instead of appending to the list ax it creates a whole new separate list. How can I append items to the array list ax through my AddTree function?

            public ListForTrees(IEnumerable<fruit_trees> trees)
            {
                foreach (fruit_trees t in trees)
                {
                    this.AddTree(t);
                }
            }



            public void AddTree(fruit_trees new_tree)
            {
                fruit_trees current = first_tree;

                if (count == 0)
                {
                    first_tree = new_tree;
                    last_tree = new_tree;
                    count = 1;
                }

                else if (count != 0)
                {
                    if (new_tree.tree_price <= first_tree.tree_price)
                    {
                        new_tree.next_tree = first_tree;
                        first_tree = new_tree;
                    }
                    else if (new_tree.tree_price >= last_tree.tree_price)
                    {
                        last_tree.next_tree = new_tree;
                        last_tree = new_tree;
                    }
                    else
                    {
                        while (new_tree.tree_price > current.next_tree.tree_price)
                        {
                            current = current.next_tree;
                        }
                        new_tree.next_tree = current.next_tree;
                        current.next_tree = new_tree;
                    }
                    count++;
                }
            }

        }

        ListForTrees mainlist = new ListForTrees();

        private void BtnGo_Click(object sender, EventArgs e)
        {
            fruit_trees[] ax = {   new fruit_trees("cherry", 48, 12.95, 3),
                                             new fruit_trees("pine", 36, 9.95, 8),
                                             new fruit_trees("oak", 60, 14.95, 2),
                                             new fruit_trees("peach", 54, 19.95, 3),
                                             new fruit_trees("pear", 36, 11.85, 2),
                                             new fruit_trees("apple", 62, 13.45, 5)
                                         };

            mainlist = new ListForTrees(ax);
            fruit_trees current = mainlist.first_tree;
            while (current != null)
            {                   
                current = current.next_tree;             
            }

        }
    }
}

Answer 1

It doesn’t seem to be creating a new separate list. I tested out the following code with yours:

public class TreeTester
{
  public static void Main(string[] args)
  {
    var list = new ListForTrees(
        new[] { new fruit_trees("tree10",10,10,10), new fruit_trees("tree2",2,2,2) });

    list.AddTree( new fruit_trees("tree3",3,3,3) );     // middle
    list.AddTree( new fruit_trees("tree1",1,1,1) );     // first
    list.AddTree( new fruit_trees("tree50",50,50,50) ); // last
    list.AddTree( new fruit_trees("tree5",5,5,5) );     // middle
    Console.Write(list);
  }
}

And got the following output, which seems correct.

tree1 1 1 1
tree2 2 2 2
tree3 3 3 3
tree5 5 5 5
tree10 10 10 10
tree50 50 50 50

What is the expected behavior, if this is not correct? Clearly these items are all being added to the original list, since they’re present when I iterate through the list.

By the way, I also added the following ToString function to your ListForTrees class; it makes debugging easier.

public override string ToString()
{
  string s = "";
  for (var tree=first_tree; tree!=null; tree = tree.next_tree)
    s += tree + "\n";
  return s;
}

---

Edit: I must comment that you may find it helpful to cleanup your code a bit in trying to understand where it is going wrong. For example, your ListForTrees(fruit_trees new_tree) constructor does the same exact thing as calling Add(new_tree) would. Also, think about three cases you have in Add, under else if (count != 0) — perhaps there’s a way they could elegantly combined into one general while loop? It makes it easier to analyze, and (potentially) less error-prone.