// pins
int led = 13, sound = 12;
int trig = 11, echo = 10;
// people count
int count;
float prev;
void setup() {
    // serial monitor setup
    Serial.begin(9600);
    // pins setup
    pinMode(led, OUTPUT);
    pinMode(sound, OUTPUT);
    pinMode(echo, INPUT);
    pinMode(trig, OUTPUT);
    // default states
    digitalWrite(led, LOW);
    digitalWrite(sound, LOW);
    digitalWrite(echo, LOW);
    count = 0;
    prev = 0;
}
void on_detect() {
    // incrementing people count
    // and printing
    count += 1;
    Serial.print("Count: ");
    Serial.println(count);
    // led blink and sound play
    digitalWrite(led, HIGH);
    tone(sound, 1024);
    delay(500);
    // setting to original state
    digitalWrite(led, LOW);
    noTone(sound);
    
void loop() {
    // sending echo
    digitalWrite(trig, HIGH);
    delay(1);
    digitalWrite(trig, LOW);
    // recieving trig
    float input = 0.17 * pulseIn(echo, HIGH);
    if (input < 1000) {
    if (!(prev != 0 && prev - 10 <= input && input <= prev + 10)) {
    prev = input;
    on_detect();
    delay(1000);
 }
 }
}