delphi7计算1+2+3+....N

unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;

type
TForm1 = class(TForm)
Button1: TButton;
Edit1: TEdit;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
i,n,sum:integer;
begin
sum :=0;
n := strToInt(edit1.text);
for i:=1 to N
sum := sum+i;
caption := inttostr(sum);
end;

end.

上学的时候没怎么学数学，不知道对不对了：

if (N mod 2) = 0 then
result := N/2 * (N + 1)
else
result := 1 + (N - 1)/2 * (N + 2);