تشخیص عدد بودن inputbox در دلفی

function IsNumber(N : String) : Boolean;

var

I : Integer;

begin

Result := True;

if Trim(N) = '' then

Exit(False);

if (Length(Trim(N)) > 1) and (Trim(N)[1] = '0') then

Exit(False);

for I := 1 to Length(N) do

begin

if not (N[I] in ['0'..'9']) then

begin

Result := False;

Break;

end;

end;

var avalue:string;

isn:boolean;

begin

avalue:=inputbox ('test1','test2','');

isn:=isnumber(avalue);

if isn=true then

showmessage('yes')

else

showmessage('no');

end;