see the instructions to do all the assignment

#include "sequence.h"
// Constructor
Sequence::Sequence()
{
numItems = 0;
tailPtr = nullptr;
headPtr = nullptr;
cursor = nullptr;
precursor = nullptr;
}
void Sequence::start()
{
if(numItems == 0) // empty sequence
cursor = nullptr;
else // Non-empty sequence
cursor = headPtr;

precursor = nullptr;
}
void Sequence::advance()
{
if(cursor == nullptr)
return;
...