Working with Parameters

Overview

Input parameters in MQL5 let you configure a program without editing its source code. By declaring variables with the input keyword, you expose them in the EA/Script settings dialog and in the Strategy Tester, making your logic flexible, testable, and ready for optimization.

What You Will Be Able to Do

• Declare configurable settings using the input keyword.
• Modify parameters from the EA properties and the Strategy Tester.
• Understand differences between input, extern (legacy), and normal variables.
• Use typed inputs (numbers, bools, enums) safely inside trading logic.

Code Example

//+------------------------------------------------------------------+
//|                                           ParametrizedEA.mq5     |
//+------------------------------------------------------------------+
#property strict
#property version   "1.00"

// ---- User-configurable inputs (visible in EA settings & Strategy Tester)
input double    Lots            = 0.10;                 // Trade lot size
input int       MAPeriod        = 20;                   // Moving Average period
input ENUM_TIMEFRAMES MaTf      = PERIOD_M5;            // MA timeframe
input ENUM_MA_METHOD MaMethod   = MODE_SMA;             // MA method
input ENUM_APPLIED_PRICE MaPrice= PRICE_CLOSE;          // Applied price
input bool      LogEveryTick    = true;                 // Verbose logging

// Example of using an enum to constrain choices
enum TradeDirection { DIR_Buy = 0, DIR_Sell = 1, DIR_None = 2 };
input TradeDirection Direction  = DIR_None;             // Planned direction

// ---- Internal state
int    maHandle = INVALID_HANDLE;

int OnInit()
  {
   // Create an MA indicator handle using current symbol, selected TF, etc.
   maHandle = iMA(_Symbol, MaTf, MAPeriod, 0, MaMethod, MaPrice);
   if(maHandle == INVALID_HANDLE)
     {
      Print("Failed to create iMA handle. Check parameters.");
      return(INIT_FAILED);
     }

   // Basic parameter sanity checks
   if(Lots <= 0.0)      { Print("Lots must be > 0");       return(INIT_PARAMETERS_INCORRECT); }
   if(MAPeriod <= 1)     { Print("MAPeriod must be > 1");  return(INIT_PARAMETERS_INCORRECT); }

   Print(StringFormat("EA initialized. Lots=%.2f, MAPeriod=%d, TF=%s, Dir=%d",
         Lots, MAPeriod, EnumToString(MaTf), Direction));
   return(INIT_SUCCEEDED);
  }

void OnDeinit(const int reason)
  {
   if(maHandle != INVALID_HANDLE) IndicatorRelease(maHandle);
   Print("EA deinitialized.");
  }

void OnTick()
  {
   // Optionally log every tick (controlled by input)
   if(LogEveryTick)
      Print("Tick at ", TimeToString(TimeCurrent(), TIME_SECONDS));

   // Read latest MA value
   double buf[];
   if(CopyBuffer(maHandle, 0, 0, 1, buf) == 1)
     {
      double ma = buf[0];
      Print(StringFormat("Latest MA(%d) on %s = %.5f", MAPeriod, EnumToString(MaTf), ma));
     }
   else
     {
      Print("CopyBuffer failed (no data yet on this timeframe?).");
     }

   // Example: use Direction input to branch logic (no live orders here)
   if(Direction == DIR_Buy)
     {
      // ... evaluate buy conditions using inputs
     }
   else if(Direction == DIR_Sell)
     {
      // ... evaluate sell conditions using inputs
     }
  }

Execution Steps

1. Open MetaEditor → File → New → Expert Advisor (template) and name it ParametrizedEA.
2. Paste the code above and press F7 to compile.
3. Attach the EA to a chart in MetaTrader 5.
4. Open the EA’s Inputs tab to change values (e.g., MAPeriod, MaTf, Direction).
5. Observe effects in the Experts log; try different inputs and verify behavior.
6. (Optional) Open the Strategy Tester, set input ranges, and run optimizations.

Key Point

Use input for user-facing, configurable settings; use normal variables for internal state. Typed inputs (including enums) make your EA safer and easier to test, and they integrate seamlessly with the Strategy Tester for optimization.

Next Section

→ Next: Reading the Log