show online users

Global.asax

Application_start
{
    Application["unm"] =0;
}
Application_end
{
   Application["unm"] =0;
}
Session_start
{
   Application.lock();
   Application["unm"] =Convert.toInt16(Application["unm"]+1);
   Application.Unlock();
}Session_end
{
   Application.lock();
   Application["unm"] =Convert.toInt16(Application["unm"]-1);
   Application.Unlock();
}

.cs file

label1.text="online users"+Application["unm"];