Expert Advisor Programming by Andrew R. Young

Order Management
Trailing Stops
We can also use our order loop to modify multiple orders. A common example of this is the trailing
stop. A trailing stop moves the stop loss up or down with the order price as the order gains in profit.
This "locks in" profit and provides excellent loss protection.
The trailing stop is expressed as a maximum number of pips. For example, if your trailing stop is 50
pips, the stop loss will never be more than 50 pips away from your price. If the price reverses and
the profit declines, the stop loss will stay where it is. The stop only moves in the direction of profit –
never in reverse.
When modifying a trailing stop, we must check to see if the distance in pips between the current
price and the current stop loss is greater that the trailing stop. If so, the stop loss will be modified so
that the distance from the current price in pips is equal to the number of pips in the trailing stop
setting.
The trailing stop is calculated relative to the closing price, which is the Bid for buy orders, and the
Ask for sell orders. Note that this is the opposite of the opening price. Let's examine the code for
modifying a trailing stop. First, we declare the external variable for our trailing stop setting:
extern double TrailingStop = 50;
This code checks all buy market orders and modifies the stop loss as necessary:
for(int Counter = 0; Counter