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Help me understand MQL4 coding

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Hi all,

 i'm studying MQL4 through the book here and documentation, i'm also watching some youtube video, but everything is before build 600+.

 So i need someone who can kindly help me adding some comment on Custom Moving Avarage Indicator, the one as example in MT4 and Moving Avarage EA.

  

//+------------------------------------------------------------------+
//|                                       Custom Moving Averages.mq4 |
//|                   Copyright 2005-2014, MetaQuotes Software Corp. |
//|                                              https://www.mql4.com |
//+------------------------------------------------------------------+
#property copyright   "2005-2014, MetaQuotes Software Corp."
#property link        "https://www.mql4.com"
#property description "Moving Average"
#property strict

#property indicator_chart_window
#property indicator_buffers 1
#property indicator_color1 Red
//--- indicator parameters
input int            InpMAPeriod=13;        // Period
input int            InpMAShift=0;          // Shift
input ENUM_MA_METHOD InpMAMethod=MODE_SMA;  // Method
//--- indicator buffer
double ExtLineBuffer[];
//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int OnInit(void)
  {
   string short_name;
   int    draw_begin=InpMAPeriod-1;
//--- indicator short name
   switch(InpMAMethod)
     {
      case MODE_SMA  : short_name="SMA(";                break;
      case MODE_EMA  : short_name="EMA(";  draw_begin=0; break;
      case MODE_SMMA : short_name="SMMA(";               break;
      case MODE_LWMA : short_name="LWMA(";               break;
      default :        return(INIT_FAILED);
     }
   IndicatorShortName(short_name+string(InpMAPeriod)+")");
   IndicatorDigits(Digits);
//--- check for input
   if(InpMAPeriod<2)
      return(INIT_FAILED);
//--- drawing settings
   SetIndexStyle(0,DRAW_LINE);
   SetIndexShift(0,InpMAShift);
   SetIndexDrawBegin(0,draw_begin);
//--- indicator buffers mapping
   SetIndexBuffer(0,ExtLineBuffer);
//--- initialization done
   return(INIT_SUCCEEDED);
  }
//+------------------------------------------------------------------+
//|  Moving Average                                                  |
//+------------------------------------------------------------------+
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[])
  {
//--- check for bars count
   if(rates_total<InpMAPeriod-1 || InpMAPeriod<2)
      return(0);
//--- counting from 0 to rates_total
   ArraySetAsSeries(ExtLineBuffer,false);
   ArraySetAsSeries(close,false);
//--- first calculation or number of bars was changed
   if(prev_calculated==0)
      ArrayInitialize(ExtLineBuffer,0);
//--- calculation
   switch(InpMAMethod)
     {
      case MODE_EMA:  CalculateEMA(rates_total,prev_calculated,close);        break;
      case MODE_LWMA: CalculateLWMA(rates_total,prev_calculated,close);       break;
      case MODE_SMMA: CalculateSmoothedMA(rates_total,prev_calculated,close); break;
      case MODE_SMA:  CalculateSimpleMA(rates_total,prev_calculated,close);   break;
     }
//--- return value of prev_calculated for next call
   return(rates_total);
  }
//+------------------------------------------------------------------+
//|   simple moving average                                          |
//+------------------------------------------------------------------+
void CalculateSimpleMA(int rates_total,int prev_calculated,const double &price[])
  {
   int i,limit;
//--- first calculation or number of bars was changed
   if(prev_calculated==0)
   
     {
      limit=InpMAPeriod;
      //--- calculate first visible value
      double firstValue=0;
      for(i=0; i<limit; i++)
         firstValue+=price[i];
      firstValue/=InpMAPeriod;
      ExtLineBuffer[limit-1]=firstValue;
     }
   else
      limit=prev_calculated-1;//
//--- main loop
   for(i=limit; i<rates_total && !IsStopped(); i++)
      ExtLineBuffer[i]=ExtLineBuffer[i-1]+(price[i]-price[i-InpMAPeriod])/InpMAPeriod;
//---
  }
//+------------------------------------------------------------------+
//|  exponential moving average                                      |
//+------------------------------------------------------------------+
void CalculateEMA(int rates_total,int prev_calculated,const double &price[])
  {
   int    i,limit;
   double SmoothFactor=2.0/(1.0+InpMAPeriod);
//--- first calculation or number of bars was changed
   if(prev_calculated==0)
     {
      limit=InpMAPeriod;
      ExtLineBuffer[0]=price[0];
      for(i=1; i<limit; i++)
         ExtLineBuffer[i]=price[i]*SmoothFactor+ExtLineBuffer[i-1]*(1.0-SmoothFactor);
     }
   else
      limit=prev_calculated-1;
//--- main loop
   for(i=limit; i<rates_total && !IsStopped(); i++)
      ExtLineBuffer[i]=price[i]*SmoothFactor+ExtLineBuffer[i-1]*(1.0-SmoothFactor);
//---
  }
//+------------------------------------------------------------------+
//|  linear weighted moving average                                  |
//+------------------------------------------------------------------+
void CalculateLWMA(int rates_total,int prev_calculated,const double &price[])
  {
   int        i,limit;
   static int weightsum;
   double     sum;
//--- first calculation or number of bars was changed
   if(prev_calculated==0)
     {
      weightsum=0;
      limit=InpMAPeriod;
      //--- calculate first visible value
      double firstValue=0;
      for(i=0;i<limit;i++)
        {
         int k=i-1;
         weightsum+=k;
         firstValue+=k*price[i];
        }
      firstValue/=(double)weightsum;
      ExtLineBuffer[limit-1]=firstValue;
     }
   else
      limit=prev_calculated-1;
//--- main loop
   for(i=limit; i<rates_total && !IsStopped(); i++)
     {
      sum=0;
      for(int j=0;j<InpMAPeriod;j++)
         sum+=(InpMAPeriod-j)*price[i-j];
      ExtLineBuffer[i]=sum/weightsum;
     }
//---
  }
//+------------------------------------------------------------------+
//|  smoothed moving average                                         |
//+------------------------------------------------------------------+
void CalculateSmoothedMA(int rates_total,int prev_calculated,const double &price[])
  {
   int i,limit;
//--- first calculation or number of bars was changed
   if(prev_calculated==0)
     {
      limit=InpMAPeriod;
      double firstValue=0;
      for(i=0; i<limit; i++)
         firstValue+=price[i];
      firstValue/=InpMAPeriod;
      ExtLineBuffer[limit-1]=firstValue;
     }
   else
      limit=prev_calculated-1;
//--- main loop
   for(i=limit; i<rates_total && !IsStopped(); i++)
      ExtLineBuffer[i]=(ExtLineBuffer[i-1]*(InpMAPeriod-1)+price[i])/InpMAPeriod;
//---
  }
//+-------------------------------------------------------------------

Here i find difficul to understand 

if(prev_calculated==0)
      ArrayInitialize(ExtLineBuffer,0);

and the for loop with all the array like the on in SMA calculation

void CalculateSimpleMA(int rates_total,int prev_calculated,const double &price[])
  {
   int i,limit;
//--- first calculation or number of bars was changed
   if(prev_calculated==0)//prima iterazione, cioè quando prev_calculated==0 
   
     {
      limit=InpMAPeriod;
      //--- calculate first visible value
      double firstValue=0;
      for(i=0; i<limit; i++)
         firstValue+=price[i];
      firstValue/=InpMAPeriod;
      ExtLineBuffer[limit-1]=firstValue;
     }
   else
      limit=prev_calculated-1;//
//--- main loop
   for(i=limit; i<rates_total && !IsStopped(); i++)
      ExtLineBuffer[i]=ExtLineBuffer[i-1]+(price[i]-price[i-InpMAPeriod])/InpMAPeriod;
//---
  }

 

The EA code is this one

//+------------------------------------------------------------------+
//|                                               Moving Average.mq4 |
//|                   Copyright 2005-2014, MetaQuotes Software Corp. |
//|                                              https://www.mql4.com |
//+------------------------------------------------------------------+
#property copyright   "2005-2014, MetaQuotes Software Corp."
#property link        "https://www.mql4.com"
#property description "Moving Average sample expert advisor"

#define MAGICMA  20131111
//--- Inputs
input double Lots          =0.1;
input double MaximumRisk   =0.02;
input double DecreaseFactor=3;
input int    MovingPeriod  =12;
input int    MovingShift   =6;
//+------------------------------------------------------------------+
//| Calculate open positions                                         |
//+------------------------------------------------------------------+
int CalculateCurrentOrders(string symbol)
  {
   int buys=0,sells=0;
//---
   for(int i=0;i<OrdersTotal();i++)
     {
      if(OrderSelect(i,SELECT_BY_POS,MODE_TRADES)==false) break;
      if(OrderSymbol()==Symbol() && OrderMagicNumber()==MAGICMA)
        {
         if(OrderType()==OP_BUY)  buys++;
         if(OrderType()==OP_SELL) sells++;
        }
     }
//--- return orders volume
   if(buys>0) return(buys);
   else       return(-sells);
  }
//+------------------------------------------------------------------+
//| Calculate optimal lot size                                       |
//+------------------------------------------------------------------+
double LotsOptimized()
  {
   double lot=Lots;
   int    orders=HistoryTotal();     // history orders total
   int    losses=0;                  // number of losses orders without a break
//--- select lot size
   lot=NormalizeDouble(AccountFreeMargin()*MaximumRisk/1000.0,1);
//--- calculate number of losses orders without a break
   if(DecreaseFactor>0)
     {
      for(int i=orders-1;i>=0;i--)
        {
         if(OrderSelect(i,SELECT_BY_POS,MODE_HISTORY)==false)
           {
            Print("Error in history!");
            break;
           }
         if(OrderSymbol()!=Symbol() || OrderType()>OP_SELL)
            continue;
         //---
         if(OrderProfit()>0) break;
         if(OrderProfit()<0) losses++;
        }
      if(losses>1)
         lot=NormalizeDouble(lot-lot*losses/DecreaseFactor,1);
     }
//--- return lot size
   if(lot<0.1) lot=0.1;
   return(lot);
  }
//+------------------------------------------------------------------+
//| Check for open order conditions                                  |
//+------------------------------------------------------------------+
void CheckForOpen()
  {
   double ma;
   int    res;
//--- go trading only for first tiks of new bar
   if(Volume[0]>1) return;
//--- get Moving Average 
   ma=iMA(NULL,0,MovingPeriod,MovingShift,MODE_SMA,PRICE_CLOSE,0);
//--- sell conditions
   if(Open[1]>ma && Close[1]<ma)
     {
      res=OrderSend(Symbol(),OP_SELL,LotsOptimized(),Bid,3,0,0,"",MAGICMA,0,Red);
      return;
     }
//--- buy conditions
   if(Open[1]<ma && Close[1]>ma)
     {
      res=OrderSend(Symbol(),OP_BUY,LotsOptimized(),Ask,3,0,0,"",MAGICMA,0,Blue);
      return;
     }
//---
  }
//+------------------------------------------------------------------+
//| Check for close order conditions                                 |
//+------------------------------------------------------------------+
void CheckForClose()
  {
   double ma;
//--- go trading only for first tiks of new bar
   if(Volume[0]>1) return;
//--- get Moving Average 
   ma=iMA(NULL,0,MovingPeriod,MovingShift,MODE_SMA,PRICE_CLOSE,0);
//---
   for(int i=0;i<OrdersTotal();i++)
     {
      if(OrderSelect(i,SELECT_BY_POS,MODE_TRADES)==false) break;
      if(OrderMagicNumber()!=MAGICMA || OrderSymbol()!=Symbol()) continue;
      //--- check order type 
      if(OrderType()==OP_BUY)
        {
         if(Open[1]>ma && Close[1]<ma)
           {
            if(!OrderClose(OrderTicket(),OrderLots(),Bid,3,White))
               Print("OrderClose error ",GetLastError());
           }
         break;
        }
      if(OrderType()==OP_SELL)
        {
         if(Open[1]<ma && Close[1]>ma)
           {
            if(!OrderClose(OrderTicket(),OrderLots(),Ask,3,White))
               Print("OrderClose error ",GetLastError());
           }
         break;
        }
     }
//---
  }
//+------------------------------------------------------------------+
//| OnTick function                                                  |
//+------------------------------------------------------------------+
void OnTick()
  {
//--- check for history and trading
   if(Bars<100 || IsTradeAllowed()==false)
      return;
//--- calculate open orders by current symbol
   if(CalculateCurrentOrders(Symbol())==0) CheckForOpen();
   else                                    CheckForClose();
//---
  }
//+------------------------------------------------------------------+

 and i find diffucult as before to understand loops.

 

Thank You 

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