Question about OnCalculate() regarding prev_calculated / rates_total / IndicatorCounted()

[Marbo]

Hi guys,

I am (still) confused about the things in the headline. I made a little test indicator which plots a dot in the middle of a candle if the candle's size is larger than its ATR(100).

Of course the indicator should only work if a new bar is printed and I still use this old IndicatorCounted() because I don't know how to use the prev_calculated and rates_total parameters.

Can anyone please tell me how to use these parameters correctly so that I can get rid of IndicatorCounted()?

#property strict
#property indicator_chart_window
#property indicator_buffers 1

double testArray[];

//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int OnInit()
  {
//--- indicator buffers mapping

   SetIndexBuffer(0, testArray);
   SetIndexStyle(0, DRAW_ARROW, 0, 2, clrYellow);
   SetIndexArrow(0, 159);
   
//---
   return(INIT_SUCCEEDED);
  }
//+------------------------------------------------------------------+
//| Custom indicator iteration function                              |
//+------------------------------------------------------------------+
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[])
  {
//---

   int Counted_bars=IndicatorCounted();
   int i=Bars-100-Counted_bars;
   while(i>0) {
      if (High[i]-Low[i]>iATR(_Symbol, _Period, 100, i)) testArray[i]=(High[i]+Low[i])/2;
      i--;
   }
//--- return value of prev_calculated for next call
   return(rates_total);
  }

[Marbo]

I tried it this way but that doesn't seem to work once a new bar is printed:

//+------------------------------------------------------------------+
//| Custom indicator iteration function                              |
//+------------------------------------------------------------------+
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[])
  {
//---

   for (int i=Bars-1-MathMax(100, prev_calculated); i>=0; --i) {
      if (High[i]-Low[i]>iATR(_Symbol, _Period, 100, i)) testArray[i]=(High[i]+Low[i])/2;
   }
//--- return value of prev_calculated for next call
   return(rates_total-1);
  }

[Alain Verleyen]

Marbo:

Hi guys,

I am (still) confused about the things in the headline. I made a little test indicator which plots a dot in the middle of a candle if the candle's size is larger than its ATR(100).

Of course the indicator should only work if a new bar is printed and I still use this old IndicatorCounted() because I don't know how to use the prev_calculated and rates_total parameters.

Can anyone please tell me how to use these parameters correctly so that I can get rid of IndicatorCounted()?

  int i=(prev_calculated==0 ? rates_total-100 : rates_total-prev_calculated);

  while(i>0)
   {
    if (high[i]-low[i]>iATR(_Symbol, _Period, 100, i)) testArray[i]=(high[i]+low[i])/2;
    i--;
   }
//--- return value of prev_calculated for next call
  return(rates_total);

On first call or when the indicator needs to be recalculated (bars on chart reached the limit "Max bars in chart" for example), prev_calculated = 0

On subsequent call, prev_calculated equals the previous rates_total (value returned at the end of OnCalculate), if it's a simple tick prev_calculated=(current) rates_total, if it's a tick with a new bar, prev_calculated = (current)rates_total-1.

rates_total is similar to "Bars".

Also use the OnCalculate() parameters high/low and not the old predefined arrays High/Low.

[Marbo]

Alain Verleyen:

On first call or when the indicator needs to be recalculated (bars on chart reached the limit "Max bars in chart" for example), prev_calculated = 0

On subsequent call, prev_calculated equals the previous rates_total (value returned at the end of OnCalculate), if it's a simple tick prev_calculated=(current) rates_total, if it's a tick with a new bar, prev_calculated = (current)rates_total-1.

rates_total is similar to "Bars".

Also use the OnCalculate() parameters high/low and not the old predefined arrays High/Low.

Great! Thank you very much!

Could you please tell me what the following means? I have never seen this kind of syntax:

int i=(prev_calculated==0 ? rates_total-100 : rates_total-prev_calculated);

[Alain Verleyen]

Marbo:

Great! Thank you very much!

Could you please tell me what the following means? I have never seen this kind of syntax:

It's the ternary operator.

It's similar to

int i;
if(prev_calculated==0)
  i=rates_total-100;
else
  i=rates_total-prev_calculated;

[William Roeder]

Marbo: I still use this old IndicatorCounted() because I don't know how to use the prev_calculated and rates_total parameters.

Can anyone please tell me how to use these parameters correctly so that I can get rid of IndicatorCounted()?

See How to do your lookbacks correctly.

[Marbo]

Alain Verleyen:

It's the ternary operator.

It's similar to

Ah, ok... so many things I have to learn. :)

[Marbo]

William Roeder:
See How to do your lookbacks correctly.

I saved your posting about lookbacks a long time ago in my bookmarks and I tried to understand it. In the second version above I tried it the new way, couting down as a time series as you described.

But as you can see I made something wrong and it didn't work as expected.