Interrupt Test Ver 1 (Flashing with delay)

const byte interruptLed = 13; // LED controlled by interrupt pin
const byte blinkLed = 4; // LED to flash for interrupt testing
int delayTime = 500; // Delay time for blinking LED
const byte interruptPin = 2; // Button connected between here and GND

// Set to 'volatile' to allow the ISR to change the variable
volatile byte state = LOW; // State of interrupt LED.

void setup()
{
  pinMode(blinkLed, OUTPUT);
  pinMode(interruptLed, OUTPUT);
  pinMode(interruptPin, INPUT_PULLUP);
  // Mode: CHANGE -> on when button pushed. RISING -> Latches On
  attachInterrupt(digitalPinToInterrupt(interruptPin), blink, RISING);
}

void loop()
 {
  flash(blinkLed);
  digitalWrite(interruptLed, state);
 }

//-------------------------------------------------------------------------

// LED flash function
void flash(byte pin)
{
 digitalWrite(pin, HIGH);
 delay(delayTime);
 digitalWrite(pin, LOW);
 delay(delayTime);
}

//-------------------------------------------------------------------------

// Interrupt Function (ISR)
void blink()
  {
  state = !state;
  }