Subtraction of alternate nodes of linked list in c#

Csharp program for Subtraction of alternate nodes of linked list. Here more information.

// Include namespace system
using System;
/*
    Csharp program for
    Subtraction of the alternate nodes of linked list
*/
// Linked list node
public class LinkNode
{
	public int data;
	public LinkNode next;
	public LinkNode(int data)
	{
		this.data = data;
		this.next = null;
	}
}
public class SingleLL
{
	public LinkNode head;
	public LinkNode tail;
	public SingleLL()
	{
		// Set initial value
		this.head = null;
		this.tail = null;
	}
	public void insert(int data)
	{
		var node = new LinkNode(data);
		if (this.head == null)
		{
			// Add first node
			this.head = node;
		}
		else
		{
			// Add node at the end position
			this.tail.next = node;
		}
		// New last node
		this.tail = node;
	}
	// Display linked list element
	public void display()
	{
		if (this.head == null)
		{
			return;
		}
		var temp = this.head;
		// iterating linked list elements
		while (temp != null)
		{
			Console.Write(" " + temp.data + " →");
			// Visit to next node
			temp = temp.next;
		}
		Console.WriteLine(" NULL");
	}
	// Find the subtraction of all alternate 
	// nodes in linked list
	public void alternateSubtraction()
	{
		// Define resultant variables
		var result = 0;
		var counter = 0;
		// Start to first node of linked list
		var temp = this.head;
		// iterating linked list elements
		while (temp != null)
		{
			if (counter % 2 == 0)
			{
				// When get alternate node
				if (result == 0)
				{
					result = temp.data;
				}
				else
				{
					result = result - temp.data;
				}
			}
			// Node counter
			counter++;
			// Visit to next node
			temp = temp.next;
		}
		Console.WriteLine(" Alternate nodes subtraction : " +
                          result);
	}
	public static void Main(String[] args)
	{
		var sll = new SingleLL();
		// Add node in linked list
		// 4 → 7 → 2 → 9 → 1 → 3 → 4 → 3 → 6 → NULL
		sll.insert(4);
		sll.insert(7);
		sll.insert(2);
		sll.insert(9);
		sll.insert(1);
		sll.insert(3);
		sll.insert(4);
		sll.insert(3);
		sll.insert(6);
		// Display of linked list nodes
		sll.display();
		// Test
		sll.alternateSubtraction();
	}
}

Output

 4 → 7 → 2 → 9 → 1 → 3 → 4 → 3 → 6 → NULL
 Alternate nodes subtraction : -9