Digital

int led = 13;
int button = 10;

int prevButtonState = LOW;
int ledState = LOW;

void setup()
{
  pinMode(led, OUTPUT);
  pinMode(button, INPUT);
}

void loop()
{
  int currentButtonState = digitalRead(button); 
  if(prevButtonState == LOW && currentButtonState == HIGH) {
    ledState = HIGH - ledState;
  }

  prevButtonState = currentButtonState;
  digitalWrite(led, ledState);
  delay(50);
}