BOLINGER BAND

Bollinger Bands consist of a middle band with two outer bands, the middle band is a simple moving average which usually set at 20 periods, the bands widen when volatility increases and narrow when volatility decreases.

//+------------------------------------------------------------------+

//|                                                        Bands.mq4 |

//|                      Copyright © 2005, MetaQuotes Software Corp. |

//|                                       http://www.metaquotes.net/ |

//+------------------------------------------------------------------+

#property copyright "Copyright © 2005, MetaQuotes Software Corp."

#property link      "http://www.metaquotes.net/"

#property indicator_chart_window

#property indicator_buffers 3

#property indicator_color1 LightSeaGreen

#property indicator_color2 LightSeaGreen

#property indicator_color3 LightSeaGreen

//---- indicator parameters

extern int    BandsPeriod=20;

extern int    BandsShift=0;

extern double BandsDeviations=2.0;

//---- buffers

double MovingBuffer[];

double UpperBuffer[];

double LowerBuffer[];

//+------------------------------------------------------------------+

//| Custom indicator initialization function                         |

//+------------------------------------------------------------------+

int init()

  {

//---- indicators

   SetIndexStyle(0,DRAW_LINE);

   SetIndexBuffer(0,MovingBuffer);

   SetIndexStyle(1,DRAW_LINE);

   SetIndexBuffer(1,UpperBuffer);

   SetIndexStyle(2,DRAW_LINE);

   SetIndexBuffer(2,LowerBuffer);

//----

   SetIndexDrawBegin(0,BandsPeriod+BandsShift);

   SetIndexDrawBegin(1,BandsPeriod+BandsShift);

   SetIndexDrawBegin(2,BandsPeriod+BandsShift);

//----

   return(0);

  }

//+------------------------------------------------------------------+

//| Bollinger Bands                                                  |

//+------------------------------------------------------------------+

int start()

  {

   int    i,k,counted_bars=IndicatorCounted();

   double deviation;

   double sum,oldval,newres;

//----

   if(Bars<=BandsPeriod) return(0);

//---- initial zero

   if(counted_bars<1)

      for(i=1;i<=BandsPeriod;i++)

        {

         MovingBuffer[Bars-i]=EMPTY_VALUE;

         UpperBuffer[Bars-i]=EMPTY_VALUE;

         LowerBuffer[Bars-i]=EMPTY_VALUE;

        }

//----

   int limit=Bars-counted_bars;

   if(counted_bars>0) limit++;

   for(i=0; i<limit; i++)

      MovingBuffer[i]=iMA(NULL,0,BandsPeriod,BandsShift,MODE_SMA,PRICE_CLOSE,i);

//----

   i=Bars-BandsPeriod+1;

   if(counted_bars>BandsPeriod-1) i=Bars-counted_bars-1;

   while(i>=0)

     {

      sum=0.0;

      k=i+BandsPeriod-1;

      oldval=MovingBuffer[i];

      while(k>=i)

        {

         newres=Close[k]-oldval;

         sum+=newres*newres;

         k--;

        }

      deviation=BandsDeviations*MathSqrt(sum/BandsPeriod);

      UpperBuffer[i]=oldval+deviation;

      LowerBuffer[i]=oldval-deviation;

      i--;

     }

//----

   return(0);

  }

//+------------------------------------------------------------------+