Nice article. A lot of people asking this question.
U can use the following code to make it easier.
PHP Code:
void AlertOnce(string alert_msg, int ref)
{
if (ref > 10)
return;
ref--;
static int LastAlert[10];
if( LastAlert[ref] == 0 || LastAlert[ref] < Bars)
{
Alert(alert_msg);
LastAlert[ref] = Bars;
}
}