83. Timer Programming

What will be printed on the serial monitor after pressing the push button switch?

Code

#define buttonPin 2
uint32_t previousValue = 0;

void handleInterrupt() {
  delay(100);
  previousValue = millis();
  delay(1000);
  Serial.println(previousValue - millis());
}

void setup() {
  Serial.begin(9600);
  pinMode(buttonPin, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(buttonPin), handleInterrupt, FALLING);
}

void loop() {
  // Controller does some important tasks.
}