Unordered list returns non equal values of integer

#include<iostream>
#include<windows.h>
using namespace std;

void init();
void push(int n);
void list();
void pop();

struct elem
{   int key;
    elem *next;
} *start,*p,*q;
elem* ordered(int index);

void init()
{
      start=NULL;
}
void push(int n)
{
      p=start;
      start=new elem;
      start->key=n;
      start->next=p;
}
void list()
{
      p=start;
      cout<<"\nЛист: ";
      while(p){
            cout<<p->key<<" ";
            p=p->next;
      }
      cout<<endl<<endl;
}

elem* ordered(int index)
{
      p=start;

      while(index)
      {
            p=p->next;
       index--;
      }

      return p;
}
int size()
{
      p=start;
      int sum=0;
      while(p->next!=NULL)
      {
            sum++;
            p=p->next;
      }

      return sum+1;

}
void pop()
{

      for(int i=0;i<size();i++)
{
for(int j=0;j<size();j++)
{
      if(i!=j)
      {
      if((ordered(i))->key==(ordered(j))->key)
      {
break;
      }
      if(j==size()-1)

      {
   cout<<ordered(i)->key;
}
}
}

      }
      }


void main()
{
int n;
init();
SetConsoleCP(1251);SetConsoleOutputCP(1251);
cout<<"Въведете число:\n";
while(cin>>n&&n!=999)
{
push(n);
}
cout<<"\nЛист :";
pop();
system("pause");
}