This EA is just a clever way of drawing lines based on the CCI values as given by:

cciTrendNow = iCCI(NULL, 0, 50, PRICE_TYPICAL, i);
cciTrendPrevious = iCCI(NULL, 0, 50, PRICE_TYPICAL, i+1);

It has been defined previously in the code that st = 0;

Then, you have
if (cciTrendNow >= st && cciTrendPrevious < st) {
TrendUp[i+1] = TrendDown[i+1];
}

if (cciTrendNow <= st && cciTrendPrevious > st) {
TrendDown[i+1] = TrendUp[i+1];
}

Thus, just put in your own EA the equivalent of the CCI functions and consider it trendup signal when
cciTrendNow >= 0 && cciTrendPrevious < 0

and trenddown signal when
cciTrendNow <= st && cciTrendPrevious > st

This indicator is nothing more but a fancy way of showing on the screen CCI crossing the 0 line.