Boolean Operators

Boolean operators — also called logical operators — combine or invert Boolean expressions. They return true or false and are essential for building complex conditions in if, while, and for statements. Arduino supports three: && (AND), || (OR), and ! (NOT).

&& (logical AND)

The && operator returns true only if both operands are true. If either operand is false, the result is false. It uses short-circuit evaluation — if the left side is false, the right side is never evaluated.

void setup() {
  Serial.begin(9600);
  pinMode(2, INPUT_PULLUP);
  pinMode(3, INPUT_PULLUP);
}

void loop() {
  int button1 = digitalRead(2);
  int button2 = digitalRead(3);

  if (button1 == LOW && button2 == LOW) {
    Serial.println("Both buttons pressed");
  } else {
    Serial.println("Not both pressed");
  }
  delay(100);
}

In this example, the message prints only when both buttons are pressed simultaneously. If either button is released, the condition evaluates to false. Short-circuit evaluation means if button1 == LOW is false, the code never checks button2.

|| (logical OR)

The || operator returns true if at least one operand is true. It also uses short-circuit evaluation — if the left side is true, the right side is skipped.

void setup() {
  Serial.begin(9600);
}

void loop() {
  int sensor1 = analogRead(A0);
  int sensor2 = analogRead(A1);

  if (sensor1 > 800 || sensor2 > 800) {
    Serial.println("At least one sensor is bright");
  } else {
    Serial.println("Both sensors are dim");
  }
  delay(500);
}

This sketch triggers a message if either light sensor reading exceeds 800. The || is useful for alarm systems, safety triggers, or any scenario where multiple conditions can each independently trigger an action.

! (logical NOT)

The ! operator inverts a Boolean value — true becomes false and false becomes true. It is a unary operator that precedes its operand.

void setup() {
  Serial.begin(9600);
  pinMode(2, INPUT_PULLUP);
}

void loop() {
  bool buttonPressed = (digitalRead(2) == LOW);

  if (!buttonPressed) {
    Serial.println("Button is released");
  }

  // Also commonly used inline
  if (!digitalRead(2)) {
    Serial.println("Also released");
  }

  delay(100);
}

Here, !buttonPressed is true when the button is not pressed. The NOT operator is also useful for toggling states:

bool ledState = false;

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  ledState = !ledState;  // toggle between true and false
  digitalWrite(LED_BUILTIN, ledState);
  delay(500);
}

This toggles the LED on and off every 500 ms by inverting ledState each time through loop(). The ! operator provides a clean way to alternate between two states without using if/else.