Link class' add, erase, find and advance member functions

[Osman Zakir]

I want to ask if I got them right, and to ask how to fix them otherwise.

Link *Link::add(Link *n)
{
 if (n == nullptr)
 {
  return this;
 }
 if (this == nullptr)
 {
  return n;
 }
 n->prev = this;
 if (succ)
 {
  succ->prev = n;
 }
 n->succ = succ;
 succ = n;
 return n;
}

Link *Link::erase()
{
 if (this == nullptr)
 {
  return nullptr;
 }
 if (succ)
 {
  succ->prev = prev;
 }
 if (prev)
 {
  prev->succ = succ;
 }
 return succ;
}

Link *Link::find(const std::string &s)
{
 while (this != nullptr)
 {
  if (value == s)
  {
   return this;
  }
  this->succ;
 }
 return nullptr;
}

const Link *Link::find(const std::string &s) const
{
 while (this != nullptr)
 {
  if (value == s)
  {
   return this;
  }
  this->succ;
 }
 return nullptr;
}

Link *Link::advance(int n) const
{
 if (this == nullptr)
 {
  return nullptr;
 }
 if (n > 0)
 {
  while (n--)
  {
   if (succ == nullptr)
   {
    return nullptr;
   }
  }
 }
 else if (n < 0)
 {
  while (n++)
  {
   if (prev == nullptr)
   {
    return nullptr;
   }
  }
 }
 return const_cast<Link *>(this);
}

I'm not sure if I got it right, so it'd be appreciated if someone would please help me out here.  Thanks in advance.