C++ Lazy deletion

#include <iostream>
#include <string>
using namespace std;
struct Node
{
int data;
bool mark;
Node *next;
};
void prepend(int x , int m, Node* &p)
{
if(m == -1 && p == NULL)
{
p = new Node;
p->data = x;
p->mark = false;
p->next = NULL;
}
else
{
Node *New = new Node;
New->data = x;
New->mark = false;
New->next = p;
p = New;
}
}
void remove(int y, Node* &p)
{
for(int i = 0; i < y; i++)
{
while(p->mark)
p = p->next;
p = p->next;
}
while(p->mark)
p = p->next;
p->mark = true;

}
void Delete(Node* &head)
{
Node* p = head;
Node* pprev;
Node* temp;
while(head != NULL && head->mark)
{
temp = head;
head = head->next;
delete temp;
p = head;
pprev = head;
}
while(p != NULL)
{
if(p->mark)
{
pprev->next = p->next;
temp = p;
p = p->next;
delete temp;
}
else
{
pprev = p;
p = p->next;
}
}
}
void clear (Node* &p)
{
Node* temp;
while(p != NULL)
{
temp = p;
p = p->next;
delete temp;
}
}
int main ()
{
string x;
int y , m = -1 , n = 0;
Node * head;
head = NULL;
Node * p;
while(x != "end")
{
cin >> x;
if(x != "end" && (x == "prepend" || x == "remove"))
cin >> y;
if(x == "prepend")
{
prepend(y , m , head);
p = head;
while(p != NULL)
{
cout << p->data;
if(p->mark)
cout << '*';
if(p->next != NULL)
cout << ' ';
p = p->next;
}
cout << endl;
m++;
}

else if(x == "remove" && y <= m && m > -1)
{
m--;
p = head;
remove(y , p);
n++;
p = head;
if(n%3 != 0)
{
while(p != NULL)
{
cout << p->data;
if(p->mark)
cout << '*';
if(p->next != NULL)
cout << ' ';
p = p->next;
}
cout << endl;
}
}
if (n%3 == 0 && n !=0 && x != "end" && x != "prepend")
{
if(m == -1)
head = NULL;
Delete(head);
p = head;
while(p != NULL)
{
cout << p->data;
if(p->next != NULL)
cout << ' ';
p = p->next;
}
if(head != NULL)
cout << endl;
if(m == -1)
head = new Node;
}

}
if(m > -1)
clear(head);
return 0;
}