Trailing stop method.

getTrailingStop.mq4

// this function requires the following parameters:
// sym = currency
// op = opening price of the current trade
// sl = stop loss price of the current trade
// ot = opening datetime of the current trade
// per = active chart's period - for calculating ATR distance properly
// type = order type of the current trade
double getTrailingStop( string sym, double op, double sl, datetime ot, int per, int type ) {
	double temp;	
	// make the result for this function initially equal the stop loss
	double result = sl;	
	// calculate the trailing stop distance
	double atr = iATR( sym, per, EXT_ATR, 1 ) * EXT_ATR_TRAILSTOP;
	// check if we are operating in the bar of entry, if so move to minute charts to find out
	// what the highest high or lowest low is since entry (rather than using the whole bar)
	// As Pepperstone timestamp their bars with the opening time of that bar we can frame
	// our logic by checking if the current bar is less than or equal to the current bar
	// if it is, then the current bar *IS* the bar of entry.
	if ( iTime( sym, per, 0 ) <= ot ) {
		temp = getMinutePrice( sym, ot, atr, type );
		if ( type == OP_BUY && temp > result ) result = temp;
		if ( type == OP_SELL && temp < result ) result = temp;
	}
	// get bars of current periods' chart	
	int b = iBars( sym, per );	
	// let's loop through the bars now, starting with the most recent bar
	for ( int i = 0; i < b; i += 1 ) {
		// if the time of the active chart is LESS than the time of when the trade opened, end
		if ( iTime( sym, per, i ) < ot ) break;
		// calculate the ATR trailing distance - using active chart's period
		// and always using the previous bar's ATR as the current bar is still
		// forming
		atr = iATR( sym, per, EXT_ATR, i+1 ) * EXT_ATR_TRAILSTOP;
		// for long trades
		if ( type == OP_BUY ) {
			// using the high of the minute chart subtract the ATR distance
			temp = iHigh( sym, per, i ) - atr;
			// compare against the current best result, and if it is better modify result
			if ( temp > result ) result = temp;
		// for short trades
		} else if ( type == OP_SELL ) {
			// using the low of the minute chart add the ATR distance
			temp = iLow( sym, per, i ) + atr;
			// compare against the current best result, and if it is better modify result
			if ( temp < result ) result = temp;
		}
	}
	// return the result, normalizing the double
	return ( N( result ) );
}

// this function will return the highest high or lowest low in the minute chart
// parameters of this function: 
// sym = currency's symbol
// ot = opening datetime of the trade
// atr = atr value used as trailing distance
// type = order type of the trade
double getMinutePrice( string sym, datetime ot, double atr, int type ) {
	int per = PERIOD_M1;
	int b = iBars( sym, per );
	// better to start with a value, rather than 0
	double result = iClose( sym, per, 0 );
	for ( int i = 0; i < b; i += 1 ) {
		// once the active bar is less than the opening time then we are analysing
		// bars PRIOR to entry, therefore exit
		if ( iTime( sym, per, i ) < ot ) break;
		if ( type == OP_BUY && iHigh( sym, per, i ) > result ) result = iHigh( sym, per, i );
		if ( type == OP_SELL && iLow( sym, per, i ) < result ) result = iLow( sym, per, i );
	}
	// now that we have found the highest value since entry let's subtract the atr distance
	if ( type == OP_BUY ) return( result - atr );
	// now that we hav found the lowest value since entry let's add the atr distance
	if ( type == OP_SELL ) return ( result + atr );
}