Expert Advisor Programming by Andrew R. Young

Order Conditions and Indicators
The first SetIndexBuffer() function sets an indicator buffer with an index of 0, and uses the array
Uptrend. We can guess from the array name that this applies to to the blue indicator line. The
second function does likewise for for the array DnTrend. Note the SetIndexStyle() functions at the
bottom that sets buffers 0 and 1 to draw a solid line.
The third buffer, with the index of 2 and the array ExtMapBuffer, is used for calculation only. We can
therefore conclude that 0 and 1 are the buffer indexes that contain our indicator price information.
Based on the array identifiers, 0 is the uptrend line, and 1 is the downtrend. Here is how we declare
our indicators:
double SlopeUp = iCustom(NULL,0,"Slope Direction Line",SlopePeriod,SlopeMethod,
SlopePrice,0,1);
double SlopeDown = iCustom(NULL,0,"Slope Direction Line",SlopePeriod,SlopeMethod,
SlopePrice,1,1);
Note that the Mode parameter – the next to last one – has been set to the appropriate indicator
buffer index – 0 for SlopeUp, and 1 for SlopeDown. The Shift parameter – the very last one – has
been set to 1, which checks the closing value of the last bar.
It's a good idea to double check that you're using the correct Mode parameters. Add a Print()
function to your expert advisor, and run a back test in the Strategy Tester using "Open prices only" as
the testing model. Make sure the Shift parameter is set to 1 in the iCustom() function.
Print("Slope Up: "+SlopeUp+", Slope Down: "+SlopeDown+" Time: "+TimeToStr(Time[1]));
The Print() function prints the value of our indicator buffers to the log, along with the time and
date of the previous bar. You can view the log under the Journal tab in the Strategy Tester window.
Here is the output of the Print() function in the log:
Slope Up: 2147483647.00000000, Slope Down: 1.50483900 Time: 2009.11.26 16:00
The value for SlopeUp, 2147483647, is a very large integer that represents the EMPTY_VALUE state of
a custom indicator. You can actually use this as a trading condition. SlopeDown returns the indicator
value of the previous bar. Time indicates the bar that we want to find on the chart.
Click the Open Chart button in the Strategy Tester window to open a chart with your indicator
already applied. Find the bar indicated in the log by Time, and make sure the indicator values in the
Data Window match those printed in the log. If not, adjust the Mode parameter in the iCustom()
function until you find the correct buffer.
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