Tug of War game on Arduino

#define BUZZER_PIN 0
#define FIRST_BAR_PIN 4
#define BAR_COUNT 10
#define MAX_SCORE 20
// global variables used in interrupts (see below)
// must be marked as unstable (volatile)
volatile int score = 0;
 
void setup ()
{
  for (int i = 0; i & lt; BAR_COUNT; ++ i)
    pinMode (i + FIRST_BAR_PIN, OUTPUT);
  pinMode (BUZZER_PIN, OUTPUT);
  // Interruption (English interrupt) suspends the main
  // program, performs the specified function, and then resumes
  // main program. We need an interrupt at the click of a button,
  // i.e. when changing the signal from high to low, i.e. on the
  // downward (falling) front
  attachInterrupt (INT1, pushP1, FALLING); // INT1 is the 3rd pin
  attachInterrupt (INT0, pushP2, FALLING); // INT0 is the 2nd pin
}
 
void pushP1 () {++ score; } // 1st player interrupt function
void pushP2 () {--score; } // 2nd player interrupt function
void loop ()
{
  tone (BUZZER_PIN, 2000, 1000); // give a signal to start.
  // while none of the players won, we update the “rope”
  while (abs (score) & lt; MAX_SCORE) {
    int bound = map (score, -MAX_SCORE, MAX_SCORE, 0, BAR_COUNT);
    int left = min (bound, BAR_COUNT / 2 - 1);
    int right = max (bound, BAR_COUNT / 2);
    for (int i = 0; i & lt; BAR_COUNT; ++ i)
      digitalWrite (i + FIRST_BAR_PIN, i & gt; = left && i & lt; = right);
  }
  tone (BUZZER_PIN, 4000, 1000); // give a signal of victory
  while (true) {} // "suspend" the board until reboot
}