void setup() {
  // Set the LED pin (D5) as an output Using DDRD register
  DDRD |= (1 << DDD5);

  // Set the button pin (D9) as an input with internal pull-up resistor Using DDRB register
  DDRB &= ~(1 << DDB1); // Clear the 1st bit to configure it as input
  PORTB |= (1 << PORTB1); // Set the 1st bit to enable the pull-up resistor
}

void loop() {
  // Flip the state of the LED pin Using PIN register to toggle the state
  PIND |= (1 << PIND5);

  // Delay based on the button state
  delay((PINB & (1 << PINB1)) ? 300 : 100);
}

/*

  const byte ledPin = 5;
  const byte buttonPin = 9;

  void setup() {
    pinMode(ledPin, OUTPUT);
    pinMode(buttonPin, INPUT_PULLUP);
  }

  void loop() {
    digitalWrite(ledPin, digitalRead(ledPin) == LOW ? HIGH : LOW); // flip pin state
    delay(digitalRead(buttonPin) == LOW ? 100 : 300); // if button is pressed wait less (but keep it visible)
  }

*/