#define BUTTON_PIN 25  // ESP32 pin GPIO25, which connected to button
#define LED_PIN    2  // ESP32 pin GPIO2, which connected to led

// variables will change:
int led_state = LOW;    // the current state of LED
int button_state;       // the current state of button

void setup() {
    // put your setup code here, to run once:
    Serial.begin(115200);
    Serial.println("Hello, ESP32!");
    pinMode(LED_PIN, OUTPUT);
    pinMode(BUTTON_PIN, INPUT_PULLUP);
    button_state = digitalRead(BUTTON_PIN);
}

void loop() {
    button_state = digitalRead(BUTTON_PIN); // read new state
    delay(100);
    if (button_state == LOW) {
      Serial.println("The button is pressed");
      // toggle state of LED
      digitalWrite(LED_PIN, HIGH);
      delay(50);
    }else{
      digitalWrite(LED_PIN, LOW);
      delay(50);
    } 
}