Variables

 Variables














Variables in Arduino are like containers that hold information. This information can be numbers, letters, or even true/false values. You need to declare a variable before you can use it, which means telling the Arduino what kind of information it will hold (its "data type") and giving it a name.

Here's a breakdown:

  • Declaration: You tell the Arduino what kind of data a variable will hold and give it a name.

    • Example: int sensorValue; This declares a variable named sensorValue that will hold integer numbers (whole numbers like -1, 0, 1, 2, etc.). int is the data type, and sensorValue is the name.

  • Data Types: Some common data types in Arduino include:

    • int: Stores integer numbers (whole numbers, positive or negative). Example: int age = 25;
    • float: Stores decimal numbers (numbers with a fractional part). Example: float temperature = 24.5;
    • char: Stores a single character (letter, number, symbol). Example: char initial = 'A';
    • boolean: Stores a true/false value. Example: boolean isButtonPressed = true;
    • String: Stores a sequence of characters (text). Example: String message = "Hello, world!";

  • Assignment: You give a variable a value using the = (assignment) operator.

    • Example: sensorValue = analogRead(A0); This reads a value from analog pin A0 and stores it in the sensorValue variable.

  • Usage: You can then use the variable's value in your code.

    • Example: Serial.println(sensorValue); This prints the value stored in the sensorValue variable to the Serial Monitor.
    • Example: if (temperature > 30.0) { Serial.println("It's hot!"); } This checks if the value of the temperature variable is greater than 30.0 and prints a message if it is.

  • Scope: The "scope" of a variable determines where in your code it can be used.

    • Global Variables: Declared outside of any function. They can be used anywhere in the program.

    • Local Variables: Declared inside a function. They can only be used within that function.

      • Example:

        int globalVariable = 10; // Global variable

void setup() {
  int localVariable = 5;  // Local variable, only usable within setup()
  Serial.begin(9600);
  Serial.println(globalVariable);  // Okay to use globalVariable here
  Serial.println(localVariable);   // Okay to use localVariable here
}

void loop() {
  Serial.println(globalVariable);  // Okay to use globalVariable here
  // Serial.println(localVariable);   // ERROR! localVariable is not defined here
}

In short, variables let you store and manipulate data in your Arduino programs. You declare them with a data type and a name, assign them values, and then use those values to control your project. The scope determines where you can access a variable.

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