blink and ring when the magnitude of noise is over 40 db

hackthon 2017.4.30

const int buzzer = 8;
// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(buzzer,OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
  char a[4];
  char b[3]={'0','4','0'};
  scanf("%c%c%c",&a[0],&a[1],&a[2]);
  for(int j=0;j<3;j++){
    if(a[j]>b[j]){
      for(int i=0;i<30;i++){
        digitalWrite(LED_BUILTIN, HIGH); 
        tone(buzzer,1000);
        delay(100);                       // wait for a second
        digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
        tone(buzzer,500);
        delay(100);         
      }
      noTone(buzzer);
      break;
    }
    else if(a[j]<b[j]) break;
  }

}