Custom Indicator MQL5: Complete Coding Tutorial for Traders 2026

//+------------------------------------------------------------------+
//|  DualSmoothMA.mq5                                                |
//|  Custom Indicator MQL5 Tutorial — Pineify.app                    |
//|  Demonstrates: buffers, inputs, OnCalculate, OnInit, OnDeinit    |
//+------------------------------------------------------------------+
#property copyright   "Pineify.app"
#property link        "https://pineify.app"
#property version     "1.00"
#property description "Dual-smoothed Moving Average — MQL5 tutorial indicator"

// Indicator drawn in the main chart window
#property indicator_chart_window

// Two indicator buffers: fast MA and slow MA
#property indicator_buffers 2
#property indicator_plots   2

//--- Plot 1: Fast MA
#property indicator_label1  "Fast MA"
#property indicator_type1   DRAW_LINE
#property indicator_color1  clrDodgerBlue
#property indicator_style1  STYLE_SOLID
#property indicator_width1  2

//--- Plot 2: Slow MA
#property indicator_label2  "Slow MA"
#property indicator_type2   DRAW_LINE
#property indicator_color2  clrOrangeRed
#property indicator_style2  STYLE_SOLID
#property indicator_width2  2

//--- Input parameters
input int    InpFastPeriod  = 9;          // Fast MA period
input int    InpSlowPeriod  = 21;         // Slow MA period
input int    InpSmoothPeriod = 3;         // Secondary smoothing period
input ENUM_MA_METHOD    InpMAMethod  = MODE_EMA;  // MA method
input ENUM_APPLIED_PRICE InpPrice    = PRICE_CLOSE; // Applied price

//--- Indicator buffers
double FastMABuffer[];
double SlowMABuffer[];

//--- Indicator handles for internal MA calculations
int handleFastMA  = INVALID_HANDLE;
int handleSlowMA  = INVALID_HANDLE;

//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int OnInit()
  {
//--- Validate input periods
   if(InpFastPeriod <= 0 || InpSlowPeriod <= 0 || InpSmoothPeriod <= 0)
     {
      Print("ERROR: All period inputs must be greater than zero.");
      return INIT_PARAMETERS_INCORRECT;
     }
   if(InpFastPeriod >= InpSlowPeriod)
     {
      Print("ERROR: Fast period must be less than slow period.");
      return INIT_PARAMETERS_INCORRECT;
     }

//--- Map arrays to indicator buffers (index matches #property indicator_buffers order)
   SetIndexBuffer(0, FastMABuffer, INDICATOR_DATA);
   SetIndexBuffer(1, SlowMABuffer, INDICATOR_DATA);

//--- Set empty value for gaps (bars not yet calculated)
   PlotIndexSetDouble(0, PLOT_EMPTY_VALUE, EMPTY_VALUE);
   PlotIndexSetDouble(1, PLOT_EMPTY_VALUE, EMPTY_VALUE);

//--- Hide warm-up samples before valid smoothed output
   PlotIndexSetInteger(0, PLOT_DRAW_BEGIN, InpFastPeriod + InpSmoothPeriod - 2);
   PlotIndexSetInteger(1, PLOT_DRAW_BEGIN, InpSlowPeriod + InpSmoothPeriod - 2);

//--- Create handles for first-pass MA (fast and slow)
   handleFastMA = iMA(_Symbol, _Period, InpFastPeriod, 0, InpMAMethod, InpPrice);
   if(handleFastMA == INVALID_HANDLE)
     {
      Print("ERROR: Failed to create fast MA handle. Error=", GetLastError());
      return INIT_FAILED;
     }

   handleSlowMA = iMA(_Symbol, _Period, InpSlowPeriod, 0, InpMAMethod, InpPrice);
   if(handleSlowMA == INVALID_HANDLE)
     {
      Print("ERROR: Failed to create slow MA handle. Error=", GetLastError());
      return INIT_FAILED;
     }

//--- Set short name visible in the Data Window
   string shortName = StringFormat("DualSmoothMA(%d,%d,%d)", InpFastPeriod, InpSlowPeriod, InpSmoothPeriod);
   IndicatorSetString(INDICATOR_SHORTNAME, shortName);

   return INIT_SUCCEEDED;
  }

//+------------------------------------------------------------------+
//| Custom indicator deinitialization function                       |
//+------------------------------------------------------------------+
void OnDeinit(const int reason)
  {
//--- Release all indicator handles to free terminal resources
   if(handleFastMA != INVALID_HANDLE)
     {
      IndicatorRelease(handleFastMA);
      handleFastMA = INVALID_HANDLE;
     }
   if(handleSlowMA != INVALID_HANDLE)
     {
      IndicatorRelease(handleSlowMA);
      handleSlowMA = INVALID_HANDLE;
     }
   Print("DualSmoothMA deinitialized. Reason code=", reason);
  }

//+------------------------------------------------------------------+
//| Custom indicator iteration function                              |
//+------------------------------------------------------------------+
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[])
  {
//--- Minimum bars needed before we can draw anything
   int minBars = InpSlowPeriod + InpSmoothPeriod;
   if(rates_total < minBars)
      return 0;

//--- Determine the starting bar for this call
//    prev_calculated == 0 means a full recalculation is required
   bool reset = (prev_calculated<=0 || prev_calculated>rates_total);
   if(reset)
     {
      ArrayInitialize(FastMABuffer,EMPTY_VALUE);
      ArrayInitialize(SlowMABuffer,EMPTY_VALUE);
     }
   int start = reset ? minBars - 1 : MathMax(minBars - 1,prev_calculated - 1);

//--- Copy fast MA values from handle into a temporary buffer
   double tempFast[];
   double tempSlow[];
   ArraySetAsSeries(tempFast, false);
   ArraySetAsSeries(tempSlow, false);

   if(CopyBuffer(handleFastMA, 0, 0, rates_total, tempFast) != rates_total)
     {
      Print("ERROR: CopyBuffer fast MA failed. Error=", GetLastError());
      return prev_calculated;
     }
   if(CopyBuffer(handleSlowMA, 0, 0, rates_total, tempSlow) != rates_total)
     {
      Print("ERROR: CopyBuffer slow MA failed. Error=", GetLastError());
      return prev_calculated;
     }

//--- Apply secondary SMA smoothing and write to output buffers
   for(int i = start; i < rates_total; i++)
     {
      //--- Fast: SMA of fast MA values over InpSmoothPeriod bars
      double sumFast = 0.0;
      double sumSlow = 0.0;
      int    count   = 0;
      for(int k = 0; k < InpSmoothPeriod && (i - k) >= 0; k++)
        {
         sumFast += tempFast[i - k];
         sumSlow += tempSlow[i - k];
         count++;
        }
      FastMABuffer[i] = (count > 0) ? sumFast / count : EMPTY_VALUE;
      SlowMABuffer[i] = (count > 0) ? sumSlow / count : EMPTY_VALUE;
     }

//--- Return the total number of bars processed
   return rates_total;
  }
//+------------------------------------------------------------------+