Arrays [i-2]

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Sorry if this is a nube question but it is driving me crazy. The first thing I'd like to say is that the time period system is annoying! I don't see why we are restricted to a limited time set. Second, I am struggling with an array issue. Why can't I write (for example) buffer[i-2]? eg consider the OBV function:

void CalculateOBV(int StartPosition,
                  int RatesCount,
                  const double &ClBuffer[],
                  const long &VolBuffer[])
  {
   for(int i=StartPosition;i<RatesCount;i++)
     {
      //--- get some data
      double Volume=VolBuffer[i];
      double PrevClose=ClBuffer[i-1];
      double CurrClose=ClBuffer[i];
      //--- fill ExtOBVBuffer
      if(CurrClose<PrevClose) ExtOBVBuffer[i]=ExtOBVBuffer[i-1]-Volume;
      else
        {
         if(CurrClose>PrevClose) ExtOBVBuffer[i]=ExtOBVBuffer[i-1]+Volume;
         else                    ExtOBVBuffer[i]=ExtOBVBuffer[i-1];
        }
     }
  }


Why can't I write:

if(CurrClose>PrevClose) ExtOBVBuffer[i]=ExtOBVBuffer[i-2]+Volume;

         else                    ExtOBVBuffer[i]=ExtOBVBuffer[i-2];


or:

double PrevClose=ClBuffer[i-2];


What  am trying to do is deal with the timeframe issue by starting with PERIOD_M1 and creating my own time spans with multiples of the 1 minute graph.

Thanks for any help...

 
Please explain your problem. Are you getting error?
 
alexvd:
Please explain your problem. Are you getting error?
I've tried this kind of approach many times in many contexts, [i-1] works but any other larger integer leads to the result that the graph disappears (although there is no error).
 
Abraham:
I've tried this kind of approach many times in many contexts, [i-1] works but any other larger integer leads to the result that the graph disappears (although there is no error).
Could you provide full source code?
 

Ok, this is basically the OBV indicator with some of the arrays in the function set to [i-2]:


//+------------------------------------------------------------------+
//|                                                          OBV.mq5 |
//|                        Copyright 2009, MetaQuotes Software Corp. |
//|                                              https://www.mql5.com |
//+------------------------------------------------------------------+
#property copyright   "2009, MetaQuotes Software Corp."
#property link        "https://www.mql5.com"
#property description "On Balance Volume"
//--- indicator settings
#property indicator_separate_window
#property indicator_buffers 1
#property indicator_plots   1
#property indicator_type1   DRAW_LINE
#property indicator_color1  DodgerBlue
#property indicator_label1  "OBV"
//--- input parametrs
input ENUM_APPLIED_VOLUME InpVolumeType=VOLUME_TICK; // Volumes
//---- indicator buffer
double                    ExtOBVBuffer[];
//+------------------------------------------------------------------+
//| On Balance Volume initialization function                        |
//+------------------------------------------------------------------+
void OnInit()
  {
//--- define indicator buffer
   SetIndexBuffer(0,ExtOBVBuffer);
//--- set indicator digits
   IndicatorSetInteger(INDICATOR_DIGITS,0);
//---- OnInit done
  }
//+------------------------------------------------------------------+
//| On Balance Volume                                                |
//+------------------------------------------------------------------+
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 &TickVolume[],
                const long &Volume[],
                const int &Spread[])
  {
//--- variables
   int    pos;
//--- check for bars count
   if(rates_total<2)
      return(0);
//--- starting calculation
   pos=prev_calculated-1;
//--- correct position, when it's first iteration
   if(pos<1)
     {
      pos=1;
      if(InpVolumeType==VOLUME_TICK)
         ExtOBVBuffer[0]=TickVolume[0];
      else ExtOBVBuffer[0]=Volume[0];
     }
    
//--- main cycle
   if(InpVolumeType==VOLUME_TICK)
    
      CalculateOBV(pos,rates_total,Close,TickVolume);

  
   else
      CalculateOBV(pos,rates_total,Close,Volume);
     
//---- OnCalculate done. Return new prev_calculated.
   return(rates_total);
  }
//+------------------------------------------------------------------+
//| Calculate OBV by volume argument                                 |
//+------------------------------------------------------------------+
void CalculateOBV(int StartPosition,
                  int RatesCount,
                  const double &ClBuffer[],
                  const long &VolBuffer[])
  {
   for(int i=StartPosition;i<RatesCount;i++)
     {
      //--- get some data
      double Volume=VolBuffer[i];
      double PrevClose=ClBuffer[i-2];
      double CurrClose=ClBuffer[i];
      //--- fill ExtOBVBuffer
      if(CurrClose<PrevClose) ExtOBVBuffer[i]=ExtOBVBuffer[i-2]-Volume;
      else
        {
         if(CurrClose>PrevClose) ExtOBVBuffer[i]=ExtOBVBuffer[i-2]+Volume;
         else                    ExtOBVBuffer[i]=ExtOBVBuffer[i-1];
        }
     }
  }
//+------------------------------------------------------------------+

 

I've tried to attach your indicator to chart. There are error.

 

 

I assume in order for you to be on the safe side, the loop should be:

for(int i=StartPosition+2;i<RatesCount;i++)
     {
      //--- get some data
      double Volume=VolBuffer[i];
      double PrevClose=ClBuffer[i-2];
      double CurrClose=ClBuffer[i];...

 for every start position>=0.

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