[PAS] Stos

program Project1;

uses
    crt, DOS;
type
  listPtr = ^list;

  list = record
       next: listPtr;
       previous: listPtr;
       x: String;
  end;

procedure push(var listStart: listPtr; var listEnd: listPtr);
var
   newElement: listPtr;
begin
     clrScr;
     if listEnd = NIL then
     begin
          newElement := listStart;
          new(newElement);
          writeLn('Wprowadz element stosu: ');
          readLn(newElement^.x);
          newElement^.next := NIL;
          newElement^.previous := NIL;
          listEnd := newElement;
          listStart := newElement;
     end else
     begin
          newElement := listEnd;
          New(newElement^.next);
          newElement := newElement^.next;
          writeLn('Wprowadz element stosu: ');
          readLn(newElement^.x);

          newElement^.next := NIL;
          newElement^.previous := listEnd;
          listEnd := newElement;
     end;
end;


procedure pop(var listStart: listPtr; var listEnd: listPtr);
var
   pointer: listPtr;
begin
     if listStart = NIL then
     begin
          clrScr;
          writeLn('Nie moge usunac - stos pusty!');
          writeLn;
          writeLn('Nacisnij dowolny klawisz, aby powrocic do menu...');
          ReadKey;
     end;
     if listStart^.next = NIL then
     begin
          pointer := listStart;
          dispose(pointer);
          listStart := NIL;
          listEnd := NIL;
     end else
     begin
          pointer := listEnd;
          listEnd := pointer^.previous;
          listEnd^.next := NIL;
          dispose(pointer);
     end;
end;


procedure isEmpty(var listStart: listPtr);
var
   pointer: listPtr;
begin
     clrScr;
     if listStart = NIL then
     begin
          WriteLn('Stos pusty!');
     end else
     begin
          writeLn('Stos NIE jest pusty!');
     end;
     writeLn;
     writeLn('Nacisnij dowolny klawisz, aby powrocic do menu...');
     ReadKey;

end;


procedure listShow(var listStart: listPtr);
var
   pointer: listPtr;
begin
     clrScr;
     pointer := listStart;
     if pointer = NIL then
     begin
          writeLn('Lista pusta!');
     end else
     begin
          writeLn('Element: ', pointer^.x);

          while pointer^.next <> NIL do
          begin
               writeLn;
               pointer := pointer^.next;
               writeLn('Element: ', pointer^.x);
          end;
     end;
     writeLn;
     writeLn('Nacisnij dowolny klawisz, aby powrocic do menu...');
     ReadKey;
end;


var
   listStart, listEnd, pointer: listPtr;
   choice: String;
begin
     listEnd:= NIL;
     listStart := NIL;

     while true do
     begin
          clrScr;
          WriteLn('1. Dodaj element do stosu');
          WriteLn('2. Usun element ze stosu');
          WriteLn('3. Sprawdz czy stos jest pusty');
          WriteLn('4. Wyswietl zawartosc stosu');
          WriteLn('0. Wyjscie');
          ReadLn(choice);
          case choice of
          '1': push(listStart, listEnd);
          '2': pop(listStart, listEnd);
          '3': isEmpty(listStart);
          '4': listShow(listStart);
          '0': break;
          end;
     end;
end.