For the linked list to be round, your tail node must reference the head of the node. So this is just the question at the end of your method Add():
toAdd.next = head;
Note that your method Add()does not iterate over all nodes of the linked list, it just does
Node current = head;
, , node, , , Add(), 2 .
node ( , ):
Node current = head;
while (current.next != head)
{
current = current.next;
}
current node , . node, , - node.
: Add() , node, NullReferenceException , - . , .