Expert Advisor Programming by Andrew R. Young

EXPERT ADVISOR PROGRAMMING
Here's how we would use the Slope Direction Line indicator in our expert advisor. If the slope is
trending upward, SlopeUp will return a price value, while SlopeDown will return EMPTY_VALUE, or
2147483647. The opposite applies when the slope is trending downward.
if(SlopeUp != EMPTY_VALUE && SlopeDown == EMPTY_VALUE) // Buy
if(SlopeUp == EMPTY_VALUE && SlopeDown != EMPTY_VALUE) // Sell
These conditions simply check to see which line is equal to EMPTY_VALUE, and which line is not.
Indicator Constants
Time Frames
Many functions in MQL, including indicator and price functions, accept a time frame parameter. As
indicated before, if we use a Timeframe parameter of 0, the current chart time frame will be used. If
we wish to use a different time frame, we will need to specify the time frame in minutes. For
example, M5 is 5, H1 is 60 and H4 is 240. We can also use constants to indicate the time frame:
• PERIOD_M1 – 1 minute.
• PERIOD_M5 – 5 minute.
• PERIOD_M15 – 15 minute.
• PERIOD_M30 – 30 minute.
• PERIOD_H1 – 1 hour (60 minutes).
• PERIOD_H4 – 4 hour (240 minutes).
• PERIOD_D1 – Daily (1440 minutes).
Applied Price
The applied price indicator parameter indicates the price series to use when calculating the indicator
value. You will generally use the close to calculate indicator values, although you may wish to use
other values as well. Here is the list of price series and their associated constants, along with the
integer value:
• PRICE_CLOSE – 0: Close price.
• PRICE_OPEN – 1: Open price.
• PRICE_HIGH – 2: High price.
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