Expert: Zlatko - 2/23/2010

Question
QUESTION: I try with this code..
but still cannot make it..
help..me sir..Thanks

void List::DisplayList()
{
  int num      =   0; //initialize counter for number of data in the list
 Node* currNode = head;
  Node* lastNode = NULL;
  while (lastNode->next != head)
  {
  cout << currNode->data << endl; //display each element
     currNode = currNode->next; //tetpkan nilai next node as the currNode
  num++; //increase counter
  }
  cout << "Number of nodes in the list: " << num << endl;
}

ANSWER: If you set lastNode to null, you cannot then ask what lastNode->next is because you cannot go "through" a NULL pointer.


Here is how you do it.

Set currNode to head
print currNode
go to currNode->next

Put the last 2 steps into a loop.
When do you stop ? When you're back at the head.

What will you do if head is NULL ?

---------- FOLLOW-UP ----------

QUESTION: If head == NULL then there will be nothing to be print
Is this true sir??
but it still cant print the correct output..
fuh..

void List::DisplayList()
{
  int num      =   0; //initialize counter for number of data in the list
  
  Node* currNode   =   head;
  
   if( head == NULL)
 // {
     cout<<"Link list is empty"<<endl;
    // return true;
 // }
  
  else
  {
  cout <<  currNode->data << endl;
  currNode = currNode->next;
  
      while (currNode == head)
      {
   cout <<  currNode->data << endl;
  currNode = currNode->next;
  num++; //increase counter
      }
  
 
  cout << "Number of nodes in the list: " << num << endl;
  }
}

Answer
That's pretty good, but your num value is one less than it should be because the first node is printed outside of the loop. Also while(currNode==head) should be while(currNode != head).

Below is a more compact way of doing it using some of your older code.

Good luck with the rest of your program. I can help you again around the same time tomorrow.

Good night.

void List::DisplayList()
{
   int num          =       0; //initialize counter for number of data in the list
   Node* currNode       =       head; //initialize start currNode dr head
   if (currNode == NULL)
   {
       cout<<"Link list is empty"<<endl;
   }
   else
   {
       do
       {
         cout << currNode->data << endl; //display each element
         currNode        =       currNode->next; //tetpkan nilai next node as the currNode
         num++; //increase counter
       }
       while (currNode != head);
   }
   
   cout << "Number of nodes in the list: " << num << endl;
}