Сортировка двусвязного списка

#include <iostream.h>
#include <conio.h>
#include <stdio.h>
struct student
{
 char name[30];
 char gruppa[10];
 char kniga[20];
 int year;
 char tel[30];
};
 
struct elem
{
  student data;
  elem *pnext;
  elem *pprev;
};
 
elem *plist=NULL, *pfirst, *pend;
int i,n;
 
void show()
{
 elem *tmp=pfirst;
 while(tmp)
  {
  cout<<"FIO studenta "<<tmp->data.name<<' '<<"Gruppa "<<tmp->data.gruppa<<" "<<"Nomer zachetki "<<tmp->data.kniga<<" "<<"God "<<tmp->data.year<<" "<<"Telefon "<<tmp->data.tel<<endl;
  tmp=tmp->pnext;
  }
}
 
void addend()
{
elem *tmp=new elem;
cout<<"Vvedite FIO stdenta ";
gets(tmp->data.name);
cout<<"Vvedite gruppy stdenta ";
gets(tmp->data.gruppa);
cout<<"Vvedite nomer zacetki stdenta ";
gets(tmp->data.kniga);
cout<<"Vvedite god rogdeniya stdenta ";
cin>>tmp->data.year;
cout<<"Vvedite nomer telefona stdenta ";
cin>>tmp->data.tel;
cout<<"\n";
if (!plist)
{
 tmp->pnext=NULL;
 plist=tmp;
 pfirst=plist;
 }
else
{
 plist->pnext=tmp;
 tmp->pnext=NULL;
 tmp->pprev=NULL;
 plist=tmp;
}
}
 
void main()
{
 cout<<"Vvedite kolichestvo studentov - ";
 cin>>n;
 cout<<"\n";
 for(i=0; i<n;i++){
 addend();
 show();}
 getch();
}