Expert Advisor Programming by Andrew R. Young

EXPERT ADVISOR PROGRAMMING
// start() function
for(int Count = CalculateBars; Count >= 0; Count--)
{
EMA[Count] = iMA(NULL,0,BandsPeriod,BandsShift,BandsMethod,BandsPrice,Count);
double StdDev = iStdDev(NULL,0,BandsPeriod,BandsShift,BandsMethod,BandsPrice,Count);
}
UpperBand[Count] = EMA[Count] + (StdDev * Deviations);
LowerBand[Count] = EMA[Count] - (StdDev * Deviations);
We've added external variables to adjust the remaining parameters for the iMA() and iStdDev()
functions. We also added a parameter to adjust the number of standard deviations. To calculate this,
we simply multiply StdDev by Deviations. Now we have a fully adjustable Bollinger Bands indicator
that is more flexible than the standard MetaTrader indicator. The full code is listed in Appendix E.
You can do more with custom indicators than just recalculate built-in indicators. Depending on your
level of mathematical knowledge, you can code indicators that aren't included with MetaTrader, or
even create your own. You can also draw and manipulate objects as well. If you'd like to learn more
about custom indicator creation, see the MQL Reference topics Custom indicators, Object functions
and Math & Trig.
Scripts
A script is an MQL program that runs only once, when it is first attached to a chart. Scripts can be
used to automate a series of trading actions, such as closing all orders on the chart or sending a
pending order. Some scripts, such as the period_converter script that ships with MetaTrader, can
redraw the chart based on a custom time period.
A script source code file should have either the show_confirm or show_inputs property directive.
The show_confirm property prompts the user to confirm the operation of the script, while
show_inputs displays the script properties dialog.
#property show_confirm
#property show_inputs
// shows confirm dialog
// shows properties dialog
If your script has parameters that need to be adjusted, use the show_inputs property. Otherwise,
use show_confirm.
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