CIRCULAR LINK LIST insert Before dalam Pascal

Insert before

program P_circular;

{$APPTYPE CONSOLE}

uses

  SysUtils;

type

  point  = ^recpoint ;

  recpoint = record

              id_mhs : string ;

              nama : string ;

              alamat : string ;

              semester : integer ;

              next,prev : point ;

             end;

var

  head,now,tail : point ;

  jawab : char ;

procedure insertBefore ;

begin

  new(now) ;

  if head = nil  then

    begin

      head := now ;

      tail := now ;

    end

  else

    begin

      now^.prev := head ;

      head^.next := now ;

    end;

  now^.next :=tail ;

  tail^.prev := now ;

  tail := now ;

end;

begin

  writeln ('INPUT DATA');

  writeln ('____________________');

  writeln ;

  repeat

    insertBefore ;

    write('masukan id :') ;readln(now^.id_mhs);

    write('masukan nama :') ;readln(now^.nama);

    write('masukan alamat :') ;readln(now^.alamat);

    write('masukan semester :') ;readln(now^.semester);

    writeln;

    write('Apakah ingin input data lagi (Y/T)? :');readln(jawab);

    writeln ;

  until upcase(jawab) = 'T' ;

  writeln('OUTPUT DATA');

  writeln('-------------------');

  now := head ;    // output

  repeat

   writeln('ID       :', now^.id_mhs);

    writeln('nama     :', now^.nama);

    writeln('alamat   :', now^.alamat);

    writeln('semester :', now^.semester);

    writeln ;

    now := now^.next ;

  until (now^.next = head^.next) ;

readln ;

end.