Extern variables are not shown in the setting pane

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Here is the official Custom Moving Average.mq5 where i replaced ''input'' by ''extern'' and all the inputs disappear from the dialog box. What is going on?

//+------------------------------------------------------------------+
//|                                        Custom Moving Average.mq5 |
//|                   Copyright 2009-2020, MetaQuotes Software Corp. |
//|                                              http://www.mql5.com |
//+------------------------------------------------------------------+
#property copyright "2009-2020, MetaQuotes Software Corp."
#property link      "http://www.mql5.com"

//--- indicator settings
#property indicator_chart_window
#property indicator_buffers 1
#property indicator_plots   1
#property indicator_type1   DRAW_LINE
#property indicator_color1  Red
//--- input parameters
extern int            InpMAPeriod=13;         // Period
extern int            InpMAShift=0;           // Shift
extern ENUM_MA_METHOD InpMAMethod=MODE_SMMA;  // Method
//--- indicator buffer
double ExtLineBuffer[];
//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
void OnInit()
  {
//--- indicator buffers mapping
   SetIndexBuffer(0,ExtLineBuffer,INDICATOR_DATA);
//--- set accuracy
   IndicatorSetInteger(INDICATOR_DIGITS,_Digits+1);
//--- set first bar from what index will be drawn
   PlotIndexSetInteger(0,PLOT_DRAW_BEGIN,InpMAPeriod);
//--- line shifts when drawing
   PlotIndexSetInteger(0,PLOT_SHIFT,InpMAShift);
//--- name for DataWindow
   string short_name;
   switch(InpMAMethod)
     {
      case MODE_EMA :
         short_name="EMA";
         break;
      case MODE_LWMA :
         short_name="LWMA";
         break;
      case MODE_SMA :
         short_name="SMA";
         break;
      case MODE_SMMA :
         short_name="SMMA";
         break;
      default :
         short_name="unknown ma";
     }
   IndicatorSetString(INDICATOR_SHORTNAME,short_name+"("+string(InpMAPeriod)+")");
//--- set drawing line empty value
   PlotIndexSetDouble(0,PLOT_EMPTY_VALUE,0.0);
  }
//+------------------------------------------------------------------+
//|  Moving Average                                                  |
//+------------------------------------------------------------------+
int OnCalculate(const int rates_total,
                const int prev_calculated,
                const int begin,
                const double &price[])
  {
   if(rates_total<InpMAPeriod-1+begin)
      return(0);
//--- first calculation or number of bars was changed
   if(prev_calculated==0)
     {
      ArrayInitialize(ExtLineBuffer,0);
      PlotIndexSetInteger(0,PLOT_DRAW_BEGIN,InpMAPeriod-1+begin);
     }
//--- calculation
   switch(InpMAMethod)
     {
      case MODE_EMA:
         CalculateEMA(rates_total,prev_calculated,begin,price);
         break;
      case MODE_LWMA:
         CalculateLWMA(rates_total,prev_calculated,begin,price);
         break;
      case MODE_SMMA:
         CalculateSmoothedMA(rates_total,prev_calculated,begin,price);
         break;
      case MODE_SMA:
         CalculateSimpleMA(rates_total,prev_calculated,begin,price);
         break;
     }
//--- return value of prev_calculated for next call
   return(rates_total);
  }
//+------------------------------------------------------------------+
//|   simple moving average                                          |
//+------------------------------------------------------------------+
void CalculateSimpleMA(int rates_total,int prev_calculated,int begin,const double &price[])
  {
   int i,start;
//--- first calculation or number of bars was changed
   if(prev_calculated==0)
     {
      start=InpMAPeriod+begin;
      //--- set empty value for first start bars
      for(i=0; i<start-1; i++)
         ExtLineBuffer[i]=0.0;
      //--- calculate first visible value
      double first_value=0;
      for(i=begin; i<start; i++)
         first_value+=price[i];
      first_value/=InpMAPeriod;
      ExtLineBuffer[start-1]=first_value;
     }
   else
      start=prev_calculated-1;
//--- main loop
   for(i=start; 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,int begin,const double &price[])
  {
   int    i,start;
   double SmoothFactor=2.0/(1.0+InpMAPeriod);
//--- first calculation or number of bars was changed
   if(prev_calculated==0)
     {
      start=InpMAPeriod+begin;
      ExtLineBuffer[begin]=price[begin];
      for(i=begin+1; i<start; i++)
         ExtLineBuffer[i]=price[i]*SmoothFactor+ExtLineBuffer[i-1]*(1.0-SmoothFactor);
     }
   else
      start=prev_calculated-1;
//--- main loop
   for(i=start; 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,int begin,const double &price[])
  {
   int    weight=0;
   int    i,l,start;
   double sum=0.0,lsum=0.0;
//--- first calculation or number of bars was changed
   if(prev_calculated<=InpMAPeriod+begin+2)
     {
      start=InpMAPeriod+begin;
      //--- set empty value for first start bars
      for(i=0; i<start; i++)
         ExtLineBuffer[i]=0.0;
     }
   else
      start=prev_calculated-1;

   for(i=start-InpMAPeriod,l=1; i<start; i++,l++)
     {
      sum   +=price[i]*l;
      lsum  +=price[i];
      weight+=l;
     }
   ExtLineBuffer[start-1]=sum/weight;
//--- main loop
   for(i=start; i<rates_total && !IsStopped(); i++)
     {
      sum             =sum-lsum+price[i]*InpMAPeriod;
      lsum            =lsum-price[i-InpMAPeriod]+price[i];
      ExtLineBuffer[i]=sum/weight;
     }
  }
//+------------------------------------------------------------------+
//|  smoothed moving average                                         |
//+------------------------------------------------------------------+
void CalculateSmoothedMA(int rates_total,int prev_calculated,int begin,const double &price[])
  {
   int i,start;
//--- first calculation or number of bars was changed
   if(prev_calculated==0)
     {
      start=InpMAPeriod+begin;
      //--- set empty value for first start bars
      for(i=0; i<start-1; i++)
         ExtLineBuffer[i]=0.0;
      //--- calculate first visible value
      double first_value=0;
      for(i=begin; i<start; i++)
         first_value+=price[i];
      first_value/=InpMAPeriod;
      ExtLineBuffer[start-1]=first_value;
     }
   else
      start=prev_calculated-1;
//--- main loop
   for(i=start; i<rates_total && !IsStopped(); i++)
      ExtLineBuffer[i]=(ExtLineBuffer[i-1]*(InpMAPeriod-1)+price[i])/InpMAPeriod;
  }
//+------------------------------------------------------------------+
 
Enaud:

Here is the official Custom Moving Average.mq5 where i replaced ''input'' by ''extern'' and all the inputs disappear from the dialog box. What is going on?

extern is not the same in MQL5 as it is in MQL4.

Use input.

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