[amibroker] First day of buy signal

[dralexchambers]

How do I find the first day of a buy in the following loop:

for (i=1; i<BarCount; i++)
{
   if (FIRST DAY OF BUY SIGNAL ONLY)
      XXX[I] = YYYY;
}

I am looking for the first day of each buy and not subsequent days in 
the buy, eg:-

Monday = No signal, or sell from previous trade
Tues = Buy   <<<- today only
Weds = In trade
Thurs = In trade
Fri = Sell

Thanks in advance.