Duplicates in list

[C++ Programming]

How to show only unique elements from this double linked list using UniqueList function? I made something, but it removes only the first...


#include "iostream"

using namespace std;

void Add(int n);
void UniqueList();

struct Elem
{
int key;
Elem *prev;
Elem *next;
} *start;

int main()
{
int num;

while(cin >> num)
{
Add(num);
}

cout key = n;
start->next = p;
start->prev = NULL;
}

void UniqueList()
{
Elem *p = start;

if(NULL != start) cout