Write a new indicator

//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
void OnInit()
  {
//--- check for input value
   if(InpWPRPeriod<3)
     {
      ExtPeriodWPR=14;
      Print("Incorrect InpWPRPeriod value. Indicator will use value=",ExtPeriodWPR);
     }
   else ExtPeriodWPR=InpWPRPeriod;
//---- name for DataWindow and indicator subwindow label
   IndicatorSetString(INDICATOR_SHORTNAME,"%R"+"("+string(ExtPeriodWPR)+")");
//---- indicator's buffer  
   SetIndexBuffer(0,ExtWPRBuffer);
   PlotIndexSetInteger(0,PLOT_DRAW_BEGIN,ExtPeriodWPR-1);
//--- digits  
   IndicatorSetInteger(INDICATOR_DIGITS,2);
//----
  }
//+------------------------------------------------------------------+
//| Williams’ Percent Range                                          |
//+------------------------------------------------------------------+
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[])
  {
//---- insufficient data
   if(rates_total<ExtPeriodWPR)
      return(0);
//--- start working
   int i=prev_calculated-1;
//--- correct position
   if(i<ExtPeriodWPR-1) i=ExtPeriodWPR-1;
//---  main cycle
   while(i<rates_total && !IsStopped())
     {
      //--- calculate maximum High
      double dMaxHigh=MaxAr(high,ExtPeriodWPR,i);
      //--- calculate minimum Low
      double dMinLow=MinAr(low,ExtPeriodWPR,i);
      //--- calculate WPR
      if(dMaxHigh!=dMinLow)
         ExtWPRBuffer[i]=-(dMaxHigh-close[i])*100/(dMaxHigh-dMinLow);
      else
         ExtWPRBuffer[i]=ExtWPRBuffer[i-1];
      //--- increment i for next iteration
      i++;
     }
   //--- return new prev_calculated value
   return(rates_total);
  }