unit Unit1;
 interface
 uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;
 type
  TMyObjectPtr = ^TMyObject;
  TMyObject = record
  First_Name: String[20];
  Last_Name: String[20];
  : TMyObjectPtr;
  end;
 type
  TForm1 = class(TForm)
  bSortByLastName: TButton;
  bDisplay: TButton;
  bPopulate: TButton;
  ListBox1: TListBox;
  bClear: TButton;
  procedure bSortByLastNameClick(Sender: TObject);
  procedure bPopulateClick(Sender: TObject);
  procedure bDisplayClick(Sender: TObject);
  procedure bClearClick(Sender: TObject);
  private
  { Private declarations }
  public
  { Public declarations }
  end;
 var
  Form1: TForm1;
  pStartOfList: TMyObjectPtr = nil;
 {List manipulation routines}
 procedure SortMyObjectListByLastName(var aStartOfList: TMyObjectPtr);
 function CreateMyObject(aFirstName, aLastName: String): TMyObjectPtr;
 procedure AppendMyObject(var aCurrentItem, aNewItem: TMyObjectPtr);
 procedure ClearMyObjectList(var aMyObject: TMyObjectPtr);
 procedure RemoveMyObject(var aStartOfList, aRemoveMe: TMyObjectPtr);
 function AreInAlphaOrder(aString1, aString2: String): Boolean;

 implementation
 {$R *.DFM}

 procedure TForm1.bClearClick(Sender: TObject);
 begin
  ClearMyObjectList(pStartOfList);
 end;
 procedure TForm1.bPopulateClick(Sender: TObject);
 var
  pNew: TMyObjectPtr;
 begin
  {Initialize the list with some static data}
  pNew := CreateMyObject('Suzy','Martinez');
  AppendMyObject(pStartOfList, pNew);
  pNew := CreateMyObject('John','Sanchez');
  AppendMyObject(pStartOfList, pNew);
  pNew := CreateMyObject('Mike','Rodriguez');
  AppendMyObject(pStartOfList, pNew);
  pNew := CreateMyObject('Mary','Sosa');
  AppendMyObject(pStartOfList, pNew);
  pNew := CreateMyObject('Betty','Hayek');
  AppendMyObject(pStartOfList, pNew);
  pNew := CreateMyObject('Luke','Smith');
  AppendMyObject(pStartOfList, pNew);
  pNew := CreateMyObject('John','Sosa');
  AppendMyObject(pStartOfList, pNew);
 end;
 procedure TForm1.bSortByLastNameClick(Sender: TObject);
 begin
  SortMyObjectListByLastName(pStartOfList);
 end;
 procedure TForm1.bDisplayClick(Sender: TObject);
 var
  pTemp: TMyObjectPtr;
 begin
  {Display the list items}
  ListBox1.Items.Clear;
  pTemp := pStartOfList;
  while pTemp <> nil do
  begin
  ListBox1.Items.Add(pTemp^.Last_Name + ', ' + pTemp.First_Name);
  pTemp := pTemp^.;
  end;
 end;
 procedure ClearMyObjectList(var aMyObject: TMyObjectPtr);
 var
  TempMyObject: TMyObjectPtr;
 begin
  {Free the memory used by the list items}
  TempMyObject := aMyObject;
  while aMyObject <> nil do
  begin
  aMyObject := aMyObject^.;
  Dispose(TempMyObject);
  TempMyObject := aMyObject;
  end;
 end;
 function CreateMyObject(aFirstName, aLastName: String): TMyObjectPtr;
 begin
  {Instantiate a new list item}
  new(result);
  result^.First_Name := aFirstName;
  result^.Last_Name := aLastName;
  result^. := nil;
 end;
 procedure SortMyObjectListByLastName(var aStartOfList: TMyObjectPtr);
 var
  aSortedListStart, aSearch, aBest: TMyObjectPtr;
 begin
  {Sort the list by the Last_Name "field"}
  aSortedListStart := nil;
  while (aStartOfList <> nil) do
  begin
  aSearch := aStartOfList;
  aBest := aSearch;
  while aSearch^. <> nil do
  begin
  if not AreInAlphaOrder(aBest^.Last_Name, aSearch^.Last_Name) then
  aBest := aSearch;
  aSearch := aSearch^.;
  end;
  RemoveMyObject(aStartOfList, aBest);
  AppendMyObject(aSortedListStart, aBest);
  end;
  aStartOfList := aSortedListStart;
 end;
 procedure AppendMyObject(var aCurrentItem, aNewItem: TMyObjectPtr);
 begin
  {Recursive function that appends the new item to the end of the list}
  if aCurrentItem = nil then
  aCurrentItem := aNewItem
  else
  AppendMyObject(aCurrentItem^., aNewItem);
 end;
 procedure RemoveMyObject(var aStartOfList, aRemoveMe: TMyObjectPtr);
 var
  pTemp: TMyObjectPtr;
 begin
  {Removes a specific item from the list and collapses the empty spot.}
  pTemp := aStartOfList;
  if pTemp = aRemoveMe then
  aStartOfList := aStartOfList^.
  else
  begin
  while (pTemp^. <> aRemoveMe) and (pTemp^. <> nil) do
  pTemp := pTemp^.;
  if pTemp = nil then Exit; //Shouldn't ever happen
  if pTemp^. = nil then Exit; //Shouldn't ever happen
  pTemp^. := aRemoveMe^.;
  end;
  aRemoveMe^. := nil;
 end;
 function AreInAlphaOrder(aString1, aString2: String): Boolean;
 var
  i: Integer;
 begin
  {Returns True if aString1 should come before aString2 in an alphabetic ascending sort}
  Result := True;
  while Length(aString2) < Length(aString1) do aString2 := aString2 + '!';
  while Length(aString1) < Length(aString2) do aString1 := aString1 + '!';
  for i := 1 to Length(aString1) do
  begin
  if aString1[i] > aString2[i] then Result := False;
  if aString1[i] <> aString2[i] then break;
  end;
 end;
 end.