How do you use OnCalculate

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I refer to the sample given in the documentation. How are we meant to use OnCalculate?

  1. With the old "start" event, we have a for loop to calculate the indicator per bar, how do we do that here with OnCalculate?
  2. why are these arguments have an ampersand, e.g. &open[]? What is the difference with the normal open[]? 
  3. why do they need to be declared here as constants? Aren't open[], close[], etc are already available normally outside having to do OnCalculate?
  4. why return(rates_total)? 
  5. Does anyone have a sample working indicator with OnCalculate?

 THANK YOU

int OnCalculate(const int rates_total,
                const int prev_calculated,
                const datetime &time[],
                const double &open[],
                const double &high[],
                const double &low[],
                const double &close[],
                const long &tick_volume[],
                const long &volume[],
                const int &spread[])
  {
//--- Get the number of bars available for the current symbol and chart period
   int bars=Bars(Symbol(),0);
   Print("Bars = ",bars,", rates_total = ",rates_total,",  prev_calculated = ",prev_calculated);
   Print("time[0] = ",time[0]," time[rates_total-1] = ",time[rates_total-1]);
//--- return value of prev_calculated for next call
   return(rates_total);
  }

 
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JD4:
When posting small portions of code, please make use of the SRC button.  If it is a large amount of code, please use "Attach file" and add the entire MQL file.

Hello Angus,

did you find how to answer all your questions?

I have the same now...


Thanks

Franco

 
See How to do your lookbacks correctly.
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