void setup() {
  // sets digital pin 8 as input to connect a switch
  pinMode(8, INPUT);  
  // generates a tone of 400Hz on output pin 7 with infinite duration
  tone(7, 400);  
}

void loop() {
  // if the switch is pressed stop the tone on pin 8
  if (digitalRead(8) == HIGH) {  
    noTone(7);  
  }
}