新手入门，简单问题

看书上的例子，但是有地方看不懂。
procedure Tmainform.FormActivate(Sender: TObject);
var
times,rn:integer;
s1,s2:string[200];
username,userpass:string[200];
myfile:file;
rt:boolean;
numread:integer;
buf1,buf2:string[200];
result:boolean;
begin
times:=1;
if login=false then          //说用来控制登陆窗口是否显示
begin
  login:=true;
repeat
  rn:=passwordDlg.ShowModal;
  if rn=mrok then
  begin
  s1:=passwordDlg.ComboBox1.Text;
  s2:=passwordDlg.Edit2.Text;
  begin
  rt:=false;
  result:=false;
  assignfile(myfile,'system.ini');
  reset(myfile,1);
    repeat
      blockread(myfile,buf1,12,numread);
      blockread(myfile,buf2,12,numread);
      if(s1=buf1)and(s2=buf2)then
      begin
        username:=s1;
        userpass:=s2;
        result:=true;
      exit;
      end;
    until(numread=0);
    closefile(myfile);
//    password:=rt;
  end;
  if result=true then
  times:=200
  else
  begin
    times:=times+1;
    if times>3 then
    close
    else
    messagedlg('密码有误,重新输入!',mtwarning,[mbok],0);
    end;
  end
  else  //rn=mrcancel
  begin
  times:=100;
  close;
  end;
  until(times>3);
if passwordDlg.ComboBox1.Text='system' then
  begin
  mainform.UpdateActions;
  pagecontrol1.ActivePage:=tabsheet1;
  end
else if passworddlg.ComboBox1.Text='renshi' then
  begin
    mainform.UpdateActions;
    pagecontrol1.ActivePage:=tabsheet1;
    tabsheet3.TabVisible:=false;
    tabsheet4.TabVisible:=false;
  end
else if passworddlg.ComboBox1.Text='caiwu' then
  begin
    mainform.UpdateActions;
    pagecontrol1.ActivePage:=tabsheet3;
    tabsheet1.TabVisible:=false;
    tabsheet2.TabVisible:=false;
  end
else if passworddlg.ComboBox1.Text='guest' then
  begin
    mainform.UpdateActions;
    pagecontrol1.ActivePage:=tabsheet1;
    tabsheet3.TabVisible:=false;
    tabsheet4.TabVisible:=false;
    tabsheet5.TabVisible:=false;
    tabsheet6.TabVisible:=false;
  end;
end;
end;
end.
说用login变量来控制登陆窗口是否显示，怎么做到的？书上没有写login定义