Writing Clean, Readable EA Code (MQL4)

Lesson Goal

In this lesson, you will learn:

• Why readable code matters more than clever code
• How professionals name variables and functions
• How to structure code so it makes sense months later
• How to avoid common beginner readability mistakes

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1) Why Clean Code Matters (Even If Your EA Works)

Many beginners think:

“If the EA works, the code is fine.”

This is not true.

Your EA will eventually need:

• Bug fixes
• New features
• Improvements

If your code is messy, you will:

• Forget what it does
• Be afraid to change it
• Accidentally break things

Clean code is not about being fancy. It is about making your future self’s life easier.

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2) Use Clear, Descriptive Names

Good names explain the code without comments.

Bad Variable Names

double x;
bool ok;
int t;

These names tell you nothing.

Good Variable Names

double RiskPercent;
bool TradingAllowed;
int MaxTrades;

You should be able to guess what a variable does just by reading its name.

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3) Name Functions Like Actions

Functions should sound like something happening.

Bad Function Names

void Func1();
void DoStuff();
void Check();

Good Function Names

void UpdateTradingRules();
void ManageOpenTrades();
void LookForEntries();

If you read your function names in order, they should describe what the EA does.

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4) Keep Functions Small and Focused

Each function should do one job only.

If a function does too many things:

• It becomes hard to understand
• It becomes hard to debug
• It becomes hard to reuse

Bad Example (Too Much in One Function)

void DoEverything()
{
   // check spread
   // check time
   // open trades
   // manage trades
   // close trades
}

Good Example (Split by Responsibility)

void UpdateTradingRules();
void LookForEntries();
void ManageOpenTrades();

One function = one responsibility.

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5) Use Spacing and Empty Lines

Spacing makes code readable.

Hard to Read

void OnTick(){UpdateTradingRules();if(!TradingAllowed)return;ManageOpenTrades();LookForEntries();}

Easy to Read

void OnTick()
{
   UpdateTradingRules();
   if(!TradingAllowed) return;

   ManageOpenTrades();
   LookForEntries();
}

Whitespace is not wasted space. It is visual clarity.

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6) Comment the WHY, Not the WHAT

Avoid comments that repeat the code.

Bad Comments

// increment i
i++;

Good Comments

// Stop trading after daily profit or loss limit is hit
if(!TradingAllowed) return;

Comments should explain:

• Why something exists
• Why a decision is made
• What rule is being enforced

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7) Organize Your EA in Clear Sections

A clean EA follows a predictable structure.

Recommended EA Layout

//==============================
// INPUTS (user settings)
//==============================

//==============================
// GLOBAL VARIABLES (EA state)
//==============================

//==============================
// ONINIT / ONDEINIT
//==============================

//==============================
// ONTICK (controller)
//==============================

//==============================
// LOGIC FUNCTIONS
//==============================

//==============================
// HELPER FUNCTIONS
//==============================

When every EA follows the same structure, you instantly feel at home in the code.

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8) Full Clean EA Example

This example shows clean naming, spacing, structure, and readability.

//==============================
// GLOBAL VARIABLES
//==============================
bool TradingAllowed = true;
datetime LastBarTime = 0;

//==============================
// ONTICK
//==============================
void OnTick()
{
   UpdateTradingRules();
   if(!TradingAllowed) return;

   if(IsNewBar())
   {
      ManageOpenTrades();
      LookForEntries();
   }
}

//==============================
// LOGIC FUNCTIONS
//==============================

void UpdateTradingRules()
{
   TradingAllowed = true;

   if(MarketInfo(Symbol(), MODE_SPREAD) > 20)
      TradingAllowed = false;
}

void ManageOpenTrades()
{
   // trailing stops, exits, breakeven logic
}

void LookForEntries()
{
   if(OrdersTotal() > 0) return;

   // entry logic here
}

//==============================
// HELPER FUNCTIONS
//==============================

bool IsNewBar()
{
   static datetime lastBar = 0;

   if(Time[0] != lastBar)
   {
      lastBar = Time[0];
      return(true);
   }
   return(false);
}

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9) Common Beginner Mistakes

• Using short, unclear variable names
• Writing very long functions
• Putting logic back into OnTick()
• Not spacing code properly
• Over-commenting obvious lines

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Lesson Summary

• Readable code is more important than clever code
• Good names reduce bugs
• Small functions are easier to manage
• Spacing and structure improve clarity
• Clean code protects your future self

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End of Section

You now understand:

• Global vs local scope
• Using void functions for reusable logic
• Organizing logic outside OnTick()
• Writing clean, readable EA code

You now have the foundation to build professional-quality Expert Advisors.

Next Up: Functions and Event Handlers -> Predefined and Custom Functions in MQL4