// Define pins for LEDs
const int greenLEDPin = 9;
const int redLEDPin = 10;

// Predefined correct password
String correctPassword = "1234";

void setup() {
  // Initialize the LED pins as outputs
  pinMode(greenLEDPin, OUTPUT);
  pinMode(redLEDPin, OUTPUT);

// Initialize Serial communication at 9600 baud rate
  Serial.begin(9600);

// Turn off both LEDs at start
  digitalWrite(greenLEDPin, LOW);
  digitalWrite(redLEDPin, LOW);

Serial.println("Enter password:");
}

void loop() {
  // Check if data is available to read
  if (Serial.available() > 0) {
    // Read the incoming string
    String inputPassword = Serial.readStringUntil('\n');

// Remove any trailing newline character
    inputPassword.trim();

// Check if the entered password matches the correct password
    if (inputPassword.equals(correctPassword)) {
      // Turn on green LED
      digitalWrite(greenLEDPin, HIGH);
      // Turn off red LED
      digitalWrite(redLEDPin, LOW);
      Serial.println("Password correct. Green light ON.");
    } else {
      // Turn off green LED
      digitalWrite(greenLEDPin, LOW);
      // Turn on red LED
      digitalWrite(redLEDPin, HIGH);
      Serial.println("Password incorrect. Red light ON.");
    }
  }
}

O Level Exam : Practical Question

🖥 Output: