Expert Advisor Programming by Andrew R. Young

EXPERT ADVISOR PROGRAMMING
Let's take a moment to talk about the Mode parameter. Some indicators draw multiple lines on the
chart. The stochastic has two. We will need to call the iStochastic() function for both the %K and
%D lines, as shown below:
double KLine = iStochastic(NULL,0,KPeriod,DPeriod,Slowing,MAMethod,Price,0,0);
double DLine = iStochastic(NULL,0,KPeriod,DPeriod,Slowing,MAMethod,Price,1,0);
Note that the Mode parameter is 0 for the %K line, and 1 for the %D line. The MQL Reference topic,
Standard Constants – Indicator lines lists the valid integer constants for the various indicators that
use the Mode parameter.
You can generate trade signals based on the relationship between the indicator lines and certain
indicator levels, such as the overbought and oversold levels of 70 and 30, respectively. You can also
evaluate trade signals based on the indicator lines' relationship to each other. For example, you may
want to open a buy order only when the %K line is above the %D line. Here are some example
conditions:
if(KLine < 70) // Buy if stochastic is not overbought
if(KLine > DLine) // Buy if %K is greater than %D
The built-in indicator functions are in the MQL Reference under Technical indicators. If you'd like
more information on an indicator's usage or method of calculation, consult the technical analysis
section of the MQL website at http://ta.mql4.com/.
Custom Indicators
Hundreds of custom indicators for MetaTrader are available online. If you decide to use a custom
indicator in your expert advisor, a little legwork will have to be done. It is best if you have the .mq4
source code file when using a custom indicator. While it is possible to use a custom indicator without
it, having the source code will make it easier to figure out the buffer indexes for the Mode parameter.
MQL has a built-in function for handling custom indicators – iCustom(). Here is the syntax:
double iCustom(string Symbol, int Timeframe, string IndicatorName, Indicator Parameters,
int Mode, int Shift);
You're already familiar with Symbol, Timeframe, Mode and Shift from earlier in the chapter. Let's
start with IndicatorName. This is the name of the indicator file, exactly as it appears in the Custom
Indicators list in the Navigator window. For example, "Slope Direction Line", or "super_signal".
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