PUSHBUTTON TOGGLE LED

// Pushbutton — toggle an LED on each press
const int BTN = 2;
const int LED = 13;
bool ledState = false;
bool lastBtn = HIGH;

void setup() {
  pinMode(BTN, INPUT_PULLUP);
  pinMode(LED, OUTPUT);
}

void loop() {
  bool btn = digitalRead(BTN);
  if (btn == LOW && lastBtn == HIGH) {  // falling edge = press
    ledState = !ledState;
    digitalWrite(LED, ledState);
    delay(20);  // debounce
  }
  lastBtn = btn;
}