Ошибка Return value of function 'rec' might be undefined

unit Unit1;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;
 
type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Button1: TButton;
    Label1: TLabel;
    Label2: TLabel;
    Label3: TLabel;
    Label4: TLabel;
    Label5: TLabel;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form1: TForm1;
  
implementation
 
{$R *.dfm}
 
function rec(k:integer):integer;
var sr:integer;
begin
if k<=0 then sr:=0
else sr:=(k mod 10)+rec(k div 10);
 
end;
 
 
procedure TForm1.Button1Click(Sender: TObject);
var k,s:integer;
begin
k:=StrToInt(Edit1.Text);
s:=0;
while k>0 do begin
s:=s+ (k mod 10);
k:=k div 10;
end;
Label1.Caption:=IntToStr(s);
Label3.Caption:=IntToStr(rec(k));
end;
end.

function rec(k:integer):integer;
begin
if k<=0 then rec:=0
else rec:=(k mod 10)+rec(k div 10);
end;

function rec(k:integer):integer;
begin
if k=0 then rec:=0
else rec:=(k mod 10)+rec(k div 10);
end;
.................
k:=abs(StrToInt(Edit1.Text));

function rec(k:integer):integer;
begin
if k=0 then rec:=0
else rec:=(k mod 10)+rec(k div 10);
end;
procedure TForm1.Button1Click(Sender: TObject);
var k:integer;
begin
k:=strtoint(Edit1.Text);
Label1.Caption:=inttostr(rec(k))
end;

procedure TForm1.Button1Click(Sender: TObject);
var k,n,s:integer;
begin
k:=StrToInt(Edit1.Text);
n:=k;
s:=0;
while k>0 do begin
s:=s+ (k mod 10);
k:=k div 10;
end;
Label1.Caption:=IntToStr(s);
Label3.Caption:=IntToStr(rec(n));
end;