Expert Advisor Programming by Andrew R. Young

Working with Functions
The arguments to our function are highlighted in bold. Other than the fact that we're using
arguments now, the code is identical to the lot size calculation code from earlier. We've added a
return statement at the end of the function – this will return the value of LotSize to our calling
function.
The function itself will be placed somewhere in our program file, outside of the start() and init()
functions, or it will be located in an external include file. In the latter case, an #include statement at
the top of the program would include the file for use in our program.
Here's how we would use this function in code. First, let's list the external variables we'll use for our
lot size settings:
extern bool DynamicLotSize = true;
extern double EquityPercent = 2;
extern double FixedLotSize = 0.1;
extern double StopLoss = 50;
And here's how we call the function. This line of code would be located inside the start() function:
double LotSize = CalcLotSize(DynamicStopLoss,EquityPercent,StopLoss,FixedLotSize);
Our external variables are passed to the function as arguments. The function will calculate our lot
size, and the value will be saved in the variable LotSize. Note that this variable is different from the
LotSize variable that is inside the CalcLotSize() function. Both variables are local to their
functions, so even though they have the same name, they are not the same variable.
Lot Verification Function
Let's continue with the lot verification code from page 51. This will be a separate function, in case
you decide to use an alternate method of calculating lot size. Regardless of the method of
determining lot size, you'll want to verify it before using passing it to an order placement function:
double VerifyLotSize(double argLotSize)
{
if(argLotSize < MarketInfo(Symbol(),MODE_MINLOT))
{
argLotSize = MarketInfo(Symbol(),MODE_MINLOT);
}
else if(argLotSize > MarketInfo(Symbol(),MODE_MAXLOT))
{
argLotSize = MarketInfo(Symbol(),MODE_MAXLOT);
}
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