boolean saida = HIGH;
int led = 4;
int botao = 3;

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

void loop() {
  int entrada = digitalRead(botao);

  if(entrada == 1)
    saida = !saida;
    digitalWrite(led, saida);
    delay(500);
    Serial.print(entrada);
    Serial.print("  ");
    Serial.println(saida);
    delay(10);
  }