//+------------------------------------------------------------------+
//|                                                       StdDev.mq5 |
//|                             Copyright 2000-2026, MetaQuotes Ltd. |
//|                                                     www.mql5.com |
//+------------------------------------------------------------------+
#property copyright   "Copyright 2000-2026, MetaQuotes Ltd."
#property link        "https://www.mql5.com"
#property description "Standard Deviation"
#include <MovingAverages.mqh>

#property indicator_separate_window
#property indicator_buffers 2
#property indicator_plots   1
#property indicator_type1   DRAW_LINE
#property indicator_color1  clrMediumSeaGreen
#property indicator_style1  STYLE_SOLID
//--- input parametrs
input int            InpStdDevPeriod=20;   // Period
input int            InpStdDevShift=0;     // Shift
input ENUM_MA_METHOD InpMAMethod=MODE_SMA; // Method
//--- indicator buffers
double ExtStdDevBuffer[];
double ExtMABuffer[];

int    ExtStdDevPeriod,ExtStdDevShift;
//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
void OnInit()
  {
//--- check for input values
   if(InpStdDevPeriod<=1)
     {
      ExtStdDevPeriod=20;
      PrintFormat("Incorrect value for input variable InpStdDevPeriod=%d. Indicator will use value %d for calculations.",
                   InpStdDevPeriod,ExtStdDevPeriod);
     }
   else
      ExtStdDevPeriod=InpStdDevPeriod;
   if(InpStdDevShift<0)
     {
      ExtStdDevShift=0;
      PrintFormat("Incorrect value for input variable InpStdDevShift=%d. Indicator will use value %d for calculations.",
                  InpStdDevShift,ExtStdDevShift);
     }
   else
      ExtStdDevShift=InpStdDevShift;
//--- define indicator buffers as indexes
   SetIndexBuffer(0,ExtStdDevBuffer);
   SetIndexBuffer(1,ExtMABuffer,INDICATOR_CALCULATIONS);
//--- set indicator short name
   string short_name=StringFormat("StdDev(%d)",ExtStdDevPeriod);
   IndicatorSetString(INDICATOR_SHORTNAME,short_name);
   PlotIndexSetString(0,PLOT_LABEL,short_name);
//--- set index shift
   PlotIndexSetInteger(0,PLOT_SHIFT,ExtStdDevShift);
  }
//+------------------------------------------------------------------+
//| Custom indicator iteration function                              |
//+------------------------------------------------------------------+
int OnCalculate(const int rates_total,const int prev_calculated,const int begin,const double &price[])
  {
   if(rates_total<ExtStdDevPeriod)
      return(0);
//--- starting work
   int start=prev_calculated-1;
//--- correct position for first iteration
   if(start<ExtStdDevPeriod)
     {
      start=ExtStdDevPeriod-1;
      ArrayInitialize(ExtStdDevBuffer,0.0);
      ArrayInitialize(ExtMABuffer,0.0);
      PlotIndexSetInteger(0,PLOT_DRAW_BEGIN,ExtStdDevPeriod-1+begin);
     }
//--- main cycle
   switch(InpMAMethod)
     {
      case  MODE_EMA :
         for(int i=start; i<rates_total && !IsStopped(); i++)
           {
            if(i==InpStdDevPeriod-1)
               ExtMABuffer[i]=SimpleMA(i,InpStdDevPeriod,price);
            else
               ExtMABuffer[i]=ExponentialMA(i,InpStdDevPeriod,ExtMABuffer[i-1],price);
            //--- Calculate StdDev
            ExtStdDevBuffer[i]=StdDevFunc(price,ExtMABuffer,i);
           }
         break;
      case MODE_SMMA :
         for(int i=start; i<rates_total && !IsStopped(); i++)
           {
            if(i==InpStdDevPeriod-1)
               ExtMABuffer[i]=SimpleMA(i,InpStdDevPeriod,price);
            else
               ExtMABuffer[i]=SmoothedMA(i,InpStdDevPeriod,ExtMABuffer[i-1],price);
            //--- Calculate StdDev
            ExtStdDevBuffer[i]=StdDevFunc(price,ExtMABuffer,i);
           }
         break;
      case MODE_LWMA :
         for(int i=start; i<rates_total && !IsStopped(); i++)
           {
            ExtMABuffer[i]=LinearWeightedMA(i,InpStdDevPeriod,price);
            ExtStdDevBuffer[i]=StdDevFunc(price,ExtMABuffer,i);
           }
         break;
      default :
         for(int i=start; i<rates_total && !IsStopped(); i++)
           {
            ExtMABuffer[i]=SimpleMA(i,InpStdDevPeriod,price);
            //--- Calculate StdDev
            ExtStdDevBuffer[i]=StdDevFunc(price,ExtMABuffer,i);
           }
     }
//--- OnCalculate done. Return new prev_calculated.
   return(rates_total);
  }
//+------------------------------------------------------------------+
//| Calculate Standard Deviation                                     |
//+------------------------------------------------------------------+
double StdDevFunc(const double &price[],const double &ma_price[],const int position)
  {
   double dev=0.0;
   for(int i=0; i<ExtStdDevPeriod; i++)
      dev+=MathPow(price[position-i]-ma_price[position],2.0);
   dev=MathSqrt(dev/ExtStdDevPeriod);
   return(dev);
  }
//+------------------------------------------------------------------+