Question

For an assignment, I need to add one objects linked list to the back of another. I have this:

WORD you("you");//where you's linked list now contains y o u
WORD are("are");//where are's linked list now contains a r e

and I want to do this:

you.Insert(are,543);//(anything greater they the current objects length is
                    //attached to the back. So that 543 can be anything > you's length

so Now, you’s linked linked list should contain:

y o u a r e

I was able to insert in the front, and anywhere in between the letters, but when I try to insert in the back the program crashes instantly. Can someone please help me figure out what is wrong? I tried using the debugger and it points to one line, but I cant figure out what is wrong. I’ve marked the line as a coming in the function:

void WORD::Insert(WORD & w, int pos)
{
if(!w.IsEmpty())
{
    alpha_numeric *r = w.Cpy();
    alpha_numeric *loc;

    (*this).Traverse(loc,pos);//pasing Traverse a pointer to a node and the     position in the list

    //if(loc == 0)
    //{
    //  alpha_numeric *k = r;//k is pointing to the begin. of the copied words list
    //  while(k -> next != 0)
    //  {
    //      k = k -> next;//k goes to the back 
    //  }
    //  k -> next = front;//k(the back) is now the front of *this
    //  front = r;//front now points to r, the copy
    //}
    else if(loc == back)
    {

        back -> next = r; //<<<-------DEBUGGER SAYS ERROR HERE?
        length += w.Length();
        while(back -> next!= 0)
        {
            back = back -> next;
        }
    }
    /*else
    {
        alpha_numeric *l = r;

        while(l -> next != 0)
        {
            l = l -> next;
        }
        l -> next = loc -> next;
        loc -> next = r;
    }
    length += w.Length();
}*/
}

Also, here is the Traverse function I used if it helps

void WORD::Traverse(alpha_numeric * & p, const int & pos)
{
if(pos <= 1)
{
    p = 0;
}
else if( pos > (*this).Length())
{
    p = back;
}
else
{
    p = front;
    for(int i = 1; i < pos - 1; i++)
    {
        p = p -> next;
    }
}

}

I DECLARED BACK AS A POINTER IN THE PRIVATE SECTION OF THE CLASS. *back

This is how I put it in the constructor

WORD::WORD()
{
alpha_numeric *p;

front = new alpha_numeric;
front = 0;
length = 0;
back = front;

for(p = front; p != 0; p = p -> next)
{
    back = back -> next;
}
}

Answer 1

*back is not pointing to the correct node in the Traverse function. It should look like this:

else if( pos > (*this).Length())
{
    alpha_numeric *k = (*this).front;
    while( k -> next != 0)
    {
        k = k -> next;
    }
    back = k;
    p = back;
}