Expert: Zlatko - 2/21/2010

Question
This program actually have 4 function.
1)AddLast = to add a new node at the last of the list
2)FindNode = to find the desired node
3)DeleteNode = to delete the desired node
4)DisplayNode = display the list

Now..my problems is with the AddLast function..
Before this I done with the AddFirst..Therefore,i try for this AddLast fuction.
I have already compile it using DevC compiler..no error listed..
But suddenly when the command prompt ask me to close the program..
I think maybe it became crash..Why???
I think the AddLast function is correct..
So,,can anyone help me to fix this crash things so that I can compile&run this code..


class List  
{
public:
       List(void) { head = NULL; }     // constructor
       ~List(void);                            // destructor

       bool IsEmpty() { return head == NULL; }
       Node* AddLast(int index, double x);      
       int FindNode(double x);  
       int DeleteNode(double x);
       void DisplayList(void);
private:
       Node* head;
};

  
Node* List::AddLast(int index,double x)     //please check for me with this AddLast function
{
     if(index<0)
     return NULL;
      
     Node* currNode=head;
      
     Node* newNode = new Node;
     newNode->data = x;
      
     if(head == NULL)
     head = newNode;  
      
     else
     {
       currNode->next = head;
       while(currNode->next !=NULL)
       {
          currNode = currNode->next;
       }
     currNode->next = newNode;
     }
}

int main()
{
   List n;
    
   n.AddLast(22,7.0);
   n.AddLast(44,5.0);
   n.AddLast(66,3.0);
   n.AddLast(88,6.0);
   n.AddLast(99,4.0);
    
   n.DisplayList();
    
    
  
}

Answer
Hello wale89

Please make sure that your Node constructor sets the Node::next pointer to NULL. You did not supply me with all the code so I can only guess at what Node looks like. Here is my version of Node

struct Node
{
   Node() {next = NULL;}

   Node* next;
   double data;
};

In List::AddLast you do not need an index parameter. What purpose would it serve ? Also the AddLast does not return anything, so declare it as void.

The biggest problem is the line currNode->next = head, right before the loop while(currNode->next !=NULL)

That line causes head to point to itself and you get an unending loop.

Here is a working version of your code.

Best regards
Zlatko




#include <stdlib.h>
struct Node
{
   Node() {next = NULL;}

   Node* next;
   double data;
};

class List
{
public:
   List(void) { head = NULL; }     // constructor
   void AddLast(double x);

private:
   Node* head;
};


void List::AddLast(double x)     //please check for me with this AddLast function
{
   Node* currNode=head;

   Node* newNode = new Node;
   newNode->data = x;

   if(head == NULL)
   {
       head = newNode;
   }
   else
   {
       //XXX this is the problem ->>>>> currNode->next = head;
       while(currNode->next !=NULL)
       {
           currNode = currNode->next;
       }
       currNode->next = newNode;
   }
   return;
}

int main()
{
   List n;

   n.AddLast(7.0);
   n.AddLast(5.0);
   n.AddLast(3.0);
   n.AddLast(6.0);
   n.AddLast(4.0);

   //n.DisplayList();

   return 0;

}