Singly Linked Circular List

Ok I'm creating a template class for a singly linked circular list. I was wondering if someone could look it over and tell me if they see any errors. I had people here go over it and have spotted some but its still not working so if anyone can take a look and let me know it would be greatly appreciated.

Code:

---

#include sclist.h



sclist::sclist()
{
        headPtr = NULL;
        size = 0;
}

sclist::~sclist()
{
//here need to delete all the nodes and set the headPtr back to NULL
//and size equal to 0

//temp count variable
int i;

//loops through starting at the front and uses the RemoveFromHead
//function to remove all the nodes till none are left at which point
//the loop is broken and size and headPtr get set back to their
//starting values of 0 and NULL respectively.
    for(i=1;i <= 5;i++)
{
        RemoveFromHead();
}
    size = 0;
    headPtr = NULL;

}       

template <class T>
void sclist::InsertAtHead(const T& data)
{
//this is a temp pointer that points to the current node
slnode<T>* currentPtr = new slnode<T>(data);

    //if there is nothing in the list
    if(headPtr == NULL)
    { 
        //sets the headPtr of the list to the newly created node
        headPtr = currentPtr;
     
        //since its a circular list the only nodes nextPtr must point to               
        //itself
        nextPtr = headPtr;
    }
   
    //if there is something in the list
    else if(headPtr != NULL)
        {
        //it will fist make a new node
        slnode = new slnode<T>(data);
     
        //it will first set the headPtr to the new node
        headPtr = slnode;
     
        //will set the nextPtr of the slnode equal to teh currentPtr
        //so that it will now point to the previous node
        nextPtr = currenPtr;     
    }
        //increments the size
        size++;     
 
}

template <class T>
void sclist::InsertAtTail(const T& data)
{
//first will walk through size times to get to the correct node then
//will take that node that has the nextPtr pointing to the head and
//set currentPtr equal to that nextPtr. Then it will have that nextPtr
//point to the new node. Then have the new nodes nextPtr set
//equal to the currentPtr.

//temp count variable
int i;

//check to see if this is the first node in the list being added and if it is
//the node will just be inserted at the head
if(headPtr = NULL)
{
    InsertAtHead();
}
else if(headPtr != NULL)
{

//will set the currentPtr back to headPtr so it starts at the beginning of
//the list

currentPtr = headPtr;       
//this for loop will go through chaging what currentPtr is equal to
    for(i=1;i<=size;i++)
    {
    currentPtr = currentPtr->nextPtr;
        }

//creates a new node with the data in it.
slnode = new slnode<T>(data);

//set the nextPTr of the new node equal to the currentPtr which will be
//pointing to the headPtr
nextPtr = currentPTr;

//sets the last end nodes nextPtr equal to the new node
nextPtr = slnode;       
}
}

//returns a pointer to the node removed from the head of the list
slnode<T>* sclist::RemoveFromHead()
{
//going to have the currentPtr set equal to the headPtr. Then set the headPtr
//equal to the nextPtr of the node we are removing from the head. Then delete
//the currentPtr because it will be pointing to the now unliked node

currentPtr = headPtr;
headPtr = headPtr->nextPtr;
delete currentPtr;

}

template <class T>
//returns a pointer to the node removed from the tail of the list.
slnode<T>* sclist::RemoveFromTail()
{

//Walk through the list size number of times.
//Set up a temp pointer named delete equal to that
//node. Then walk through the list again but this time size-1 times and
//set that nodes nextPtr  equal to headPtr.Then delete the delete pointer

//temp count variable
int i;

//the tempPtr named tempEnd
T* delete = new delete;

//set currentPtr equal to the head
delete = head;

//the for loop to walk to the end of the list
for(i=1;i<=size;i++)
{
    delete = delete->nextPtr;
}

//now will go through size-1 times
for(i=1;i<=size-1;i++)
{
    currentPtr = currentPtr->nextPtr;
}

//this leaves the previous tail node unlinked
nextPtr = headPtr;

//deletes the unlinked node
delete delete;


}

template <class T>
//true if the list is empty, otherwise false.
bool sclist::IsEmpty()
{

//if the headPtr is equal to null then its empty;
if(headPtr == NULL)
{
    IsEmpty = true;
}
else
{
    IsEmpty = false;
}

}

template <class T>
//moves headPtr one node forward in the list.
void sclist::Advance()
{

//is just advancing one spot so just set currentPtr equal to the nextPtr
currentPtr = currentPtr->nextPtr;

}

template <class T>
//returns a pointer to the first node in the list, starting from the head of
//the list,that contains the indicated data. If the data is not in the list,
//returns NULL.
slnode<T>* sclist::Locate(T data)
{

//will first set currentPtr equal to head. Then it will advance one at a
//time and check the data to see if it matches the data in the parameter.
//If not it will continue to move on. A if statement will be used here.

//a temporary counter so that when or if the data is found it will have a
//number that will correspond to where in the size it is.
int count;

if(*currentPtr != data)
{
    Advance();
    //need an if statement to see if its at the end of the list will compare
    //count to the size if they are equal it will stop and print not found.
   
    if(size = count)
    {
        cout << "Data not found." << endl;
        break;
    }
    count++;
}

//if the data is found
else if(*currentPtr == data)
{
    //will print the count number the data is located at and then break.
    cout << "Data found at node #" << count << endl;
    break;
}

}

---

What does #include sclist.h look like? For example sclist::Advance() uses a currentPtr, which isn't declared locally, so it must be declared in sclist? And is * overloaded in the scnode class to get at the data, so that this line (if(*currentPtr != data)) works?

sclist.h

Code:

---

#ifndef SCLIST_H
#define SCLIST_H

#include "slnode.h"

template<class T>
class sclist
{
    public:
        //default constructor
        sclist();
       
        //deconstructor
        ~sclist();
       
        //inserts a node at the head of the list
        void InsertAtHead(const T&);

        //inserts a node at the tail of the list
        void InsertAtTail(const T&);
       
        //returns a pointer to the node removed
        //from the head of the list       
        slnode<T>* RemoveFromHead();
       
        //returns a pointer to the node removed
        //from the tail of the list
        slnode<T>* RemoveFromTail();
       
        //true if the list is empty, otherwise false
        bool IsEmpty();
       
        //moves headPtr one node forward in the list
        void Advance();
       
        //returns a pointer to the first node in the list
        //starting from the head of the list, that contains
        //the indicated data. If the data is not in the list,
        //returns NULL.
        slnode<T>* Locate(T data);
       
    private:
        T* headPtr;
        int size;
};
#include "sclist.template"

#endif

---

If the list is circular, you don't need a tail.

Code:

---

    //if there is nothing in the list
    if(headPtr == NULL)
    { 
        //sets the headPtr of the list to the newly created node
        headPtr = currentPtr;
     
        //since its a circular list the only nodes nextPtr must point to               
        //itself
        nextPtr = headPtr;
    }
   
    //if there is something in the list
    else if(headPtr != NULL)
        {
        //it will fist make a new node
        slnode = new slnode<T>(data);

---

You already know it's not NULL because you just checked for that. No need to do it again.

Code:

---

     
        //it will first set the headPtr to the new node
        headPtr = slnode;

---

This shouldn't be done until you've fixed up the pointers. You should set "slnode->next = headPtr;" before this.


Quzah.