Introduction to MQL for Traders: Understanding Code Structure and Key Functions

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If you're a trader looking to automate your trading strategies using MetaTrader, understanding the structure of MQL (MetaQuotes Language) is crucial.

MQL is the programming language behind the powerful tools that make MetaTrader so flexible, allowing you to create custom indicators, Expert Advisors (EAs), and scripts. This thread will walk you through the key elements of MQL code and explain the core functions that every trader should know.

The Structure of MQL Code​

MQL code is organized into different sections depending on the type of program you're writing: Expert Advisors (EAs), custom indicators, or scripts. Let’s focus on the basic structure that applies to each type.

1. Expert Advisors (EAs)​

These are automated trading systems that execute trades based on the rules you define. The key functions in an EA include:

• OnInit(): This function is executed when the program is initialized. It is used for setting up the initial parameters.
• OnTick(): This is the heart of an EA. It’s executed every time the market price changes and is where you define your trading logic.
• OnDeinit(): This function is triggered when the EA is removed from the chart and is used for cleanup operations.

Example:

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2. Custom Indicators​

These are tools used to analyze market conditions and display visual data (like moving averages or RSI). Indicators don’t execute trades but provide important insights.

• OnInit(): Sets up the indicator parameters.
• OnCalculate(): Called every time a new price tick arrives and is responsible for calculating and updating the indicator values.

Example:

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3. Scripts​

These are simple programs that perform specific tasks. They run once when triggered and can be used to automate tasks like opening/closing orders or modifying trade parameters.

• OnStart(): The function that runs when the script is executed. It’s the entry point for scripts.

Example:

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Key Functions Every Trader Should Know​

Here are some of the most important functions in MQL that every trader should become familiar with:

• OrderSend(): This function is used to place orders (buy, sell, etc.). It requires several parameters, including the symbol, order type, lot size, and price.

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• OrderClose(): Used to close an open order. It requires the order ticket and the closing price.

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• Print(): A simple debugging tool that outputs text to the log. It’s very useful for troubleshooting and tracking variable values during code execution.

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• GetLastError(): Returns the last error code. It’s essential for troubleshooting when something goes wrong with an order or other function.

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• iMA(): The moving average function, used to calculate the moving average of a given symbol. It’s useful for creating trading strategies based on market trends.

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• OrderSelect(): Used to select an order from the history or open orders. Once selected, you can use other functions to retrieve order information.

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Organizing MQL Code for Readability​

A well-organized MQL code is easier to debug and maintain. Here are some tips:

• Use functions: Break your code into smaller, reusable functions to keep it clean and modular.
• Add comments: Always comment your code to explain what each part does, especially the more complex sections.
• Indent properly: Proper indentation makes your code easier to read.

Conclusion​

Understanding the structure and key functions of MQL is essential for automating trading strategies in MetaTrader. Whether you're building an Expert Advisor, a custom indicator, or a script, mastering the fundamentals of MQL will allow you to unlock the full potential of MetaTrader’s capabilities.

Start by experimenting with simple programs, testing them in the MetaTrader Strategy Tester, and gradually advancing to more complex systems. Happy coding and trading!

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