void setup() {
pinMode(13, OUTPUT);
pinMode(12,OUTPUT);
pinMode(3, INPUT);
pinMode(5, OUTPUT);
pinMode(6, OUTPUT);
}

void loop() {
digitalWrite(5, LOW);
delayMicroseconds(2);
digitalWrite(5, HIGH);
delayMicroseconds(10);
digitalWrite(5, LOW);
long Duration = pulseIn(3, HIGH);
int distance = Duration*0.034/2;
Serial.print("distance= ");
Serial.print(distance);
Serial.println("cm");
if(distance<=50) {
digitalWrite(13, HIGH);
digitalWrite(12, LOW);
digitalWrite(6, HIGH);
tone (6,262,500);
delay(10);
}
else if (distance>50) {
digitalWrite(12, HIGH);
digitalWrite(13, LOW);
digitalWrite(6, LOW);
delay(10);
}
}