ultrasonic sensor not working

import RPi.GPIO as GPIO
import time

# Define GPIO pins
TRIG = 24
ECHO = 18

def setup():
    # Set up the GPIO mode
    GPIO.setmode(GPIO.BCM)
    
    # Set up TRIG as an output and ECHO as an input
    GPIO.setup(TRIG, GPIO.OUT)
    GPIO.setup(ECHO, GPIO.IN)

    # Ensure TRIG is set low initially
    GPIO.output(TRIG, False)
    print("Waiting for sensor to settle")
    time.sleep(2)

def measure_distance():
    # Send a 10us pulse to TRIG
    GPIO.output(TRIG, True)
    time.sleep(0.00001)
    GPIO.output(TRIG, False)

    # Wait for the ECHO to go high (start of the echo pulse)
    while GPIO.input(ECHO) == 0:
        pulse_start = time.time()

    # Wait for the ECHO to go low (end of the echo pulse)
    while GPIO.input(ECHO) == 1:
        pulse_end = time.time()

    # Calculate the duration of the pulse
    pulse_duration = pulse_end - pulse_start

    # Calculate the distance (speed of sound is 34300 cm/s)
    distance = pulse_duration * 34300 / 2

    return distance

def cleanup():
    GPIO.cleanup()

if __name__ == "__main__":
    try:
        setup()
        while True:
            distance = measure_distance()
            print(f"Distance: {distance:.2f} cm")
            time.sleep(1)
    except KeyboardInterrupt:
        print("Measurement stopped by User")
        cleanup()