// a boool can only exsist in only two states
// true or false, 1 or 0, HIGH or LOW
// any none zerp interger will give you a true uotput
// 1,15,-10,-1 is true

int led = 13;
bool state = false;

void setup() {
  Serial.begin(9600);
  pinMode(led, OUTPUT);
}

void loop() {
  digitalWrite(led, state);
  delay(1000);
  state=!state;
}