In this article you will learn about MQL5 Variables and how essentials they are in building your own indicators and EAs.
What are MQL5 Variables?
Variables are the foundation of any programming language, and MQL5 is no exception.
In MQL5, variables store data that can be manipulated and used throughout your trading algorithms.
Understanding how to declare, initialize, and use variables properly is essential for writing clean and efficient code.
To give another definition…
MQL5 Variables are named containers for storing data. This data can be of different types like numbers, text, or boolean values. Variables allow your program to remember and manipulate information during execution.
Official MQL5 documentation defines variables here.
To give an analogy also, think of a variable like a labeled box where you can store a value (numbers, text, dates, or other types of information) and retrieve or modify it when needed.
Variables are crucial because they allow your program to process and react to different inputs and conditions
Why Do We Need Variables in MQL5?
Awesome question, do we actually need variables? Answer is Yes and No…
If you code something simple you can probably hardcode values in you program, and it will work, however, placing set values in the code usually prevents a sufficient level of flexibility.
So we could say that variables are essential because they provide a way to store and reuse data, data that can also be modified.
Without variables, every value would have to be hardcoded, making your code inflexible and difficult to maintain.
By using variables, you can easily adjust your logic, store intermediate results, and manage complex algorithms.
How to Use MQL5 Variables
You will quickly become familiar with the use of variables, you have no choice, and it will make you a much better MQL5 coder.
There are very few and simple actions needed to use variables.
Declaring Variables
Declaring a variable means telling the MQL5 compiler that a variable exists and specifying its type. The type determines what kind of data the variable can hold.
The syntax to declare a variable is simply <data type> <name of the variable>;
Syntax:
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int tradeCount; string currencyPair; bool isActive; |
In this example:
tradeCountis an integer.currencyPairis a string.isActiveis a boolean.
Initializing Variables
Initializing a variable means giving it an initial value at the time of declaration.
Syntax:
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int tradeCount = 5; string currencyPair = "EURUSD"; bool isActive = true; |
You can also declare a variable first and assign a value later:
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int tradeCount; tradeCount = 5; |
Modifying Variables
Modifying a variable means updating or replacing the value stored in it.
Syntax is similar to initialization but without the data type.
Syntax:
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orderCount += 1; currentPrice = SymbolInfoDouble("EURUSD", SYMBOL_ASK); isTrading = false; message = "Trading paused"; |
Using Variables
Once declared and initialized, variables can be used in calculations, conditions, and function calls.
You can read their values, modify them, and pass them as arguments.
To do any of that you only need to write the name of the variable where you want to use it
Example:
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int trades = 10; if (trades > 0) { Print("You have open trades: ", trades); } trades += 5; Print("Updated trade count: ", trades); |
In this example:
- The
tradesvariable stores the number of open trades. - We check its value in an
ifstatement. - We update its value and print the result.
Types of Variables in MQL5
We talk more about MQL5 Data Types in other articles, but in short, MQL5 supports various data types, including:
- Integer Types:
int,long,short - Floating-Point Types:
double,float - Boolean:
bool - Character:
char - String:
string - Date and Time:
datetime - Color:
color
Choosing the right type is crucial for efficient memory usage and performance.
Scope of MQL5 Variables
Scope is a very important concept to understand in the context of variables and constants.
The ccope is the simply the boundaries where a variable or constant exists and can be used.
Again, the scope of a variable determines where it can be accessed:
- Local Variables: Declared within a function and accessible only there.
- Global Variables: Declared outside any function and accessible throughout the program.
Example:
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int globalVariable = 100; // Global void CheckTrades() { int localVariable = 10; // Local Print("Local: ", localVariable); Print("Global: ", globalVariable); } |
Conclusion
MQL5 variables are a powerful and flexible way to store and manage data in your trading programs.
By understanding how to declare, initialize, and use variables properly, you can write more efficient and maintainable code.
We really only scratched the surface of variables to allow you to get started, mastering variables is a critical step toward becoming proficient in MQL5 programming.
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