Expert Advisor Programming by Andrew R. Young

EXPERT ADVISOR PROGRAMMING
// Lot size calculation
if(DynamicLotSize == true)
{
double RiskAmount = AccountEquity() * (EquityPercent / 100);
double TickValue = MarketInfo(Symbol(),MODE_TICKVALUE);
if(Point == 0.001 || Point == 0.00001) TickValue *= 10;
double CalcLots = (RiskAmount / StopLoss) / TickValue;
double LotSize = CalcLots;
}
else LotSize = FixedLotSize;
// Lot size verification
if(LotSize < MarketInfo(Symbol(),MODE_MINLOT))
{
LotSize = MarketInfo(Symbol(),MODE_MINLOT);
}
else if(LotSize > MarketInfo(Symbol(),MODE_MAXLOT))
{
LotSize = MarketInfo(Symbol(),MODE_MAXLOT);
}
if(MarketInfo(Symbol(),MODE_LOTSTEP) == 0.1)
{
LotSize = NormalizeDouble(LotSize,1);
}
else LotSize = NormalizeDouble(LotSize,2);
The lot size calculation and verification code from page 51 is added to the beginning of our start
function. Since our stop loss level is known beforehand, this is a good a place as any to put it. The
remaining code is our modified buy market order routine:
// Buy Order
if(FastMA > SlowMA && BuyTicket == 0)
{
// Close Order
OrderSelect(SellTicket,SELECT_BY_TICKET);
if(OrderCloseTime() == 0 && SellTicket > 0)
{
double CloseLots = OrderLots();
while(IsTradeContextBusy()) Sleep(10);
RefreshRates();
double ClosePrice = Ask;
bool Closed = OrderClose(SellTicket,CloseLots,ClosePrice,UseSlippage,Red);
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