HELP!

[itfreakas]

Hello everyone, I have this working program with operations on circular doubly linked list. But I have one slight problem, for example when there is only one node in the list and when I try to remove it with my remove function, afterwards instead of printing that the list is now empty, it prints me garbage like 41096232 or crashes, why is that?

#include <iostream>
#include <fstream>
#include <vector>
#include <cstdlib>
using namespace std;

struct node
{
    int info;
    node *next;
    node *prev;
}
*start, *last;
int counter = 0;

class double_clist
{
    public:
        node *create_node(int);
        void insert_file(int value);
        void insert_begin();
        void insert_last();
        void insert_pos();
        void delete_pos();
        void display();
        void display_file();
        double_clist()
        {
            start = 0;
            last = 0;
        }
};

int main()
{
    double_clist cdl;

    ifstream fin("1.txt");
    int value;
    if (!fin)
    {
        cout << "Error! Unable to read a text file " << "1.txt" << endl << endl;
        return -1;
    }
    while(fin >> value)
    {
        cdl.insert_file(value);
    }

    cout << "Formed circular doubly linked list:" << endl;
    cdl.display();
    cdl.display_file();

    int choice;
    while (1)
    {
        cout << "OPERATIONS ON CIRCULAR DOUBLY LINKED LIST!" << endl << endl;
        cout << "1. Insert element in the begining!" << endl << endl;
        cout << "2. Insert element in the end!" << endl << endl;
        cout << "3. Insert element in the middle!" << endl << endl;
        cout << "4. Remove element from the position!" << endl << endl;
        cout << "5. Display elements on the screen!" << endl <<endl;
        cout << "6. End program!" << endl << endl;
        cout << "Enter your choice: ";
        cin >> choice;
        switch(choice)
        {
        case 1:
            cdl.insert_begin();
            cdl.display();
            break;
        case 2:
            cdl.insert_last();
            cdl.display();
            break;
        case 3:
            cdl.insert_pos();
            cdl.display();
            break;
        case 4:
            cdl.delete_pos();
            cdl.display();
            break;
        case 5:
            cdl.display();
            break;
        case 6:
            cdl.display_file();
            system("start results.txt");
            exit(1);
        default:
            cout << "Wrong choice!" << endl << endl;
        }
    }
    return 0;
}

node* double_clist::create_node(int value)
{
    counter++;
    struct node *temp;
    temp = new(struct node);
    temp->info = value;
    temp->next = 0;
    temp->prev = 0;
    return temp;
}

void double_clist::insert_file(int value)
{
    struct node *temp;
    temp = create_node(value);
    if (start == last && start == 0)
    {
        cout << "Elements are successfully read from the text file!" << "1.txt" << "!" << endl << endl;
        start = last = temp;
        start->next = last->next = 0;
        start->prev = last->prev = 0;
    }
    else
    {
        last->next = temp;
        temp->prev = last;
        last = temp;
        start->prev = last;
        last->next = start;
    }
}

void double_clist::insert_begin()
{
    int value;
    cout << endl << "Enter the element which you want to insert at the beginning: ";
    cin >> value;
    struct node *temp;
    temp = create_node(value);
    if (start == last && start == 0)
    {
        cout << "Element successfully inserted!" << endl << endl;
        start = last = temp;
        start->next = last->next = 0;
        start->prev = last->prev = 0;
    }
    else
    {
        temp->next = start;
        start->prev = temp;
        start = temp;
        start->prev = last;
        last->next = start;
        cout << "Element successfully inserted!" << endl << endl;
    }
}

void double_clist::insert_last()
{
    int value;
    cout << endl<<"Enter the element which you want to insert at the end: ";
    cin >> value;
    struct node *temp;
    temp = create_node(value);
    if (start == last && start == 0)
    {
        cout << "Element successfully inserted!" << endl << endl;
        start = last = temp;
        start->next = last->next = 0;
        start->prev = last->prev = 0;
    }
    else
    {
        last->next = temp;
        temp->prev = last;
        last = temp;
        start->prev = last;
        last->next = start;
        cout << "Element successfully inserted!" << endl << endl;
    }
}

void double_clist::insert_pos()
{
    int value, pos, i;
    cout << endl << "Enter the element which you want to insert: ";
    cin >> value;
    cout << endl << "Enter the position: ";
    cin >> pos;
    struct node *temp, *s, *ptr;
    temp = create_node(value);
    if (start == last && start == 0)
    {
        if (pos == 1)
        {
            start = last = temp;
            start->next = last->next = 0;
            start->prev = last->prev = 0;
        }
        else
        {
            cout << "Position is unavailable!" << endl << endl;
            counter--;
            return;
        }
    }
    else
    {
        if (counter < pos)
        {
             cout << "Position is unavailable!" << endl << endl;
             counter--;
             return;
        }
        s = start;
        for (i = 1;i <= counter;i++)
        {
            ptr = s;
            s = s->next;
            if (i == pos - 1)
            {
                ptr->next = temp;
                temp->prev = ptr;
                temp->next = s;
                s->prev = temp;
                cout << "Element successfully inserted!" << endl << endl;
                break;
            }
        }
    }
}

void double_clist::delete_pos()
{
    int pos, i;
    node *ptr, *s;
    if (start == last && start == 0)
    {
        cout << "Circular doubly linked list is empty!" << endl << endl;
        return;
    }
    cout << "Enter the position of the elements which you want to remove: ";
    cin >> pos;
    if (counter < pos)
    {
        cout << "Position is unavailable!" << endl << endl;
        return;
    }
    s = start;
    if(pos == 1)
    {
        counter--;
        last->next = s->next;
        s->next->prev = last;
        start = s->next;
        delete(s);
        cout << "Element successfully removed!" << endl << endl;
        return;
    }
    for (i = 0;i < pos - 1;i++ )
    {
        s = s->next;
        ptr = s->prev;
    }
    ptr->next = s->next;
    s->next->prev = ptr;
    if (pos == counter)
    {
        last = ptr;
    }
    counter--;
    delete(s);
    cout << "Element successfully removed!" << endl << endl;
}

void double_clist::display()
{
    int i;
    struct node *s;
    if (start == last && start == 0)
    {
        cout << "Circular doubly linked list is empty!" << endl << endl;
        return;
    }
    s = start;
    for (i = 0;i < counter-1;i++)
    {
        cout <<s->info << "<->";
        s = s->next;
    }
    cout <<s->info << endl << endl;
}

void double_clist::display_file()
{
    ofstream fout;
    fout.open("results.txt", ios::app);
    int i;
    struct node *s;
    if (start == last && start == 0)
    {
        fout << "Circular doubly linked list is empty!" << endl << endl;
        return;
    }
    s = start;
    for (i = 0;i < counter-1;i++)
    {
        fout<<s->info<<"<->";
        s = s->next;
    }
    fout << s->info << endl << endl;
    fout.close();
}

[kbw]

Your delete method doesn't reset the pointers to null, which is your invariant state for empty. So the object doen't know when it's empty.

You can improve the usability of your list my making start and last members of the class. That way you can instantiate many different instances of lists.

The methods should just take the values or positions to be processed. They shouldn't prompt the user. That will allow more flexible use.