Create Linked list in Memory

type
  TMyObjectPtr = ^TMyObject;
  TMyObject = record
    First_Name: String[20];
    Last_Name: String[20];
    Next: TMyObjectPtr;
  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;

//

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^.Next;
    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^.Next := 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^.Next <> nil do
    begin
      if not AreInAlphaOrder(aBest^.Last_Name, aSearch^.Last_Name) then
        aBest := aSearch;
      aSearch := aSearch^.Next;
    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^.Next, 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^.Next
  else
  begin
    while (pTemp^.Next <> aRemoveMe) and (pTemp^.Next <> nil) do
      pTemp := pTemp^.Next;
    if pTemp = nil then Exit; //Shouldn't ever happen
    if pTemp^.Next = nil then Exit; //Shouldn't ever happen
    pTemp^.Next := aRemoveMe^.Next;
  end;
  aRemoveMe^.Next := 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;

// Clear
procedure TForm1.Button1Click(Sender: TObject);
begin
  ClearMyObjectList(pStartOfList);
end;

// Populare
procedure TForm1.Button2Click(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;

// Sort List
procedure TForm1.Button3Click(Sender: TObject);
begin
  SortMyObjectListByLastName(pStartOfList);
end;

// Display List
procedure TForm1.Button4Click(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^.Next;
  end;
end;