help with double link list

[bonnie1702]

Hi all,

I have a double link list program that compiles ok, and when I run it, I get a message box saying that windows needs to stop the program.
Here is the code:

#include <iostream>
#include <conio.h>

using namespace std;

class linklist
{
      private:
             struct dnode
             {
                 dnode *prev;
                 int data;
                 dnode *next;
             }*p;
      public:
             linklist();
             ~linklist();
             void d_addatbeg(int num);
             void d_append(int num);
             void d_addafter(int loc,int num);
             void d_delete(int num);
};

linklist::linklist()
{
   p = NULL;
}

linklist::~linklist()
{
   dnode *q;
   while (q->next != NULL)
   {
      q = p->next;
      delete p;
      p = q;
   }
}

void linklist::d_addatbeg(int num)
{
     dnode *q;
     q = new dnode;
     q->prev = NULL;
     q->data = num;
     q->next = p;
     p->prev = q;
     p = q;
}

void linklist::d_append(int num)
{
     dnode *q,*r;
     q = p;
     if (q == NULL)
     {
         q = new dnode;
         q->prev = NULL;
         q->data = num;
         q->next = NULL;
         p = q;
     }
     else
     {
         while (q->next != NULL)
            q = q->next;
            r = new dnode;
            r->data = num;
            r->next = NULL;
            r->prev = q;
            q->next = r;
     }
}

void linklist::d_addafter(int loc,int num)
{
     dnode *q;
     q = p;
     for (int i = 0;i < loc;i++)
     {
         q = q->next;
         if (q == NULL)
         {
             cout << "There are less than " << loc << " elements";
             return;
         }
     }
     q = q->prev;
     dnode *temp = new dnode;
     temp->data = num;
     temp->prev = q;
     temp->next = q->next;
     temp->next->prev = temp;
     q->next = temp;
}

void linklist::d_delete(int num)
{
     dnode *q = p;
     while (q != NULL)
     {
        if (q->data == num)
          if (q == p)
          {
              p = p->next;
              p->prev = NULL;
          }
          else
          {
              if (q->next = NULL)
                q->prev->next = NULL;
              else
              {
                  q->prev->next = q->next;
                  q->next->prev = q->prev;
              }
              delete q;
          }
          return;
     }
     q = q->next;

     cout << "\n" << num << " not found";
}

int main()
{
    linklist P;
    cout << "Adding at beginning: " << endl;
    P.d_addatbeg(33);
    P.d_addatbeg(55);
    getch();
    return 0;
}//end main

I am not sure where I have gone wrong and would appreciate it if someone could give some advice?
Thanks in advance

[cikara21]

Check you destructor

[ArkM]

Not only destructor: d_addatbeg is wrong too (see empty list case)...

Please, use code tag correctly:
[code=cplusplus] source

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