Savoir si un string ne comporte que des chiffres

function IsStrANumber( const S: String): Boolean;
var
P:PChar;

begin
P:=PChar(S);
result:=False;
while P^ <> #130 do
begin
if not (P^ in ['0'..'9']) then exit;
inc(P);
end;
result:=True;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
if IsStrANumber(edit1.text)=false then
ShowMessage('Pas composé uniquement de ch if fres');
end;