Linked List Implementation by Structure In C#()

Question

I am implementing Linked List in C# so I use Two Approaches

First Approach

 unsafe public struct Node
        {
            public int info;
            public Node* link;
        }

Here Is Add Node Method

public void AddNode( int  a)
        {
            Node temp = new Node();
            temp.info = a;
               if (Head == null)
               {
                  Head = Current = &temp;        
               }
            else
            {
                    (*Current).link = &temp;  
                     Current = &temp; 
                }                                         
            }

When I run This Code It does not save memory means It create an instance of Node temp = new Node();Structure as long as it is inside AddNode Its memory is save but when I print It outside this method using Head its give me NullRefrenceException

Second Approach

By Using Class And Objects

    public class Node
        {
            public int info;
            public Node link;
        }
        class Linked_list
        {
           public Node Head;
           public Node Current;



            public void insert_element_linkedlist( int  a)
            {
                Node temp = new Node();
                temp.info = a;
                   if (Head == null)
                   {
                      Head = Current = temp;        
                   }
                else
                {
                        Current.link = temp;  
                         Current = temp; 
                    }                                         
                } 
}

The Second method is working perfectly means Every instance of temp node Node temp = new Node(); is save in memory .

Question : Why It does not save structure instance ?

Sorry For My Sub Standard English.

Answer 1

The structure instance, being a value type, gets created on the stack, so when AddNode returns it is cleaned up and you are left with pointers to a random place in memory. Simply creating a pointer to a variable is not enough to keep it alive.