Question from a newbie code learner - page 2

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double Prev_HA_Open = iCustom(NULL,PERIOD_H4,"heikinashi",2,1);
double Prev_HA_Close = iCustom(NULL,PERIOD_H4,"heikinashi",3,1);
double HA_Open = (Prev_HA_Open+Prev_HA_Close)/2;
double HA_Close = (iOpen(Symbol(),PERIOD_H4,1)+iHigh(Symbol(),PERIOD_H4,1)+iLow(Symbol(),PERIOD_H4,1)+iClose(Symbol(),PERIOD_H4,1))/4;
double Current_Low = iLow(Symbol(),PERIOD_H4,1);
double Current_High = iHigh(Symbol(),PERIOD_H4,1);  


double HA_Low = MathMin(
                        MathMin(Current_Low, 
                                HA_Open),
                        HA_Close
                       );

double HA_High = MathMax(
                         MathMin(Current_High,
                                 HA_Open),
                         HA_Close
                        );

Those are not assignments; they are initialization of a common (globally declared), or static variable with a constant. They work exactly the same way in MT4/MT5/C/C++.

  1. They are initialized once on program load.

  2. They don't update unless you assign to them.

  3. In C/C++ you can only initialize them with constants, and they default to zero. In MTx you should only initialize them with constants. There is no default in MT5, or MT4 with strict (which you should always use).

    MT4/MT5 actually compiles with non-constants, but the order that they are initialized is unspecified and

    Don't try to use any price or server related functions in OnInit (or on load), as there may be no connection/chart yet:

    1. Terminal starts.
    2. Indicators/EAs are loaded. Static and globally declared variables are initialized. (Do not depend on a specific order.)
    3. OnInit is called.
    4. For indicators OnCalculate is called with any existing history.
    5. Human may have to enter password, connection to server begins.
    6. New history is received, OnCalculate called again.
    7. New tick is received, OnCalculate/OnTick is called. Now TickValue, TimeCurrent, account information and prices are valid.
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