Why does my HCR04 ultrasonic sensor give randome readings?

I'm using an HC-SR04 ultrasonic sensor with my Arduino to measure distance, but I'm getting inconsistent readings. Sometimes it works fine, but other times the values jump around randomly, even when there's no object moving.

Here's my code:

const int trigPin = 7;
const int echoPin = 6;

void setup() {
    Serial.begin(9600);
    pinMode(trigPin, OUTPUT);
    pinMode(echoPin, INPUT);
}

void loop() {
    digitalWrite(trigPin, LOW);
    delayMicroseconds(2);
    digitalWrite(trigPin, HIGH);
    delayMicroseconds(10);
    digitalWrite(trigPin, LOW);

    long duration = pulseIn(echoPin, HIGH);
    int distance = duration * 0.034 / 2;

    Serial.println(distance);
    delay(500);
}

The issues I am facing:

• The sensor sometimes returns very high or very low values randomly.
• The readings are unstable even when there’s a fixed object in front of it.
• Sometimes I even get 0 cm, even though there’s no obstacle that close.