#define LED_PIN 8
#define BUTTON_PIN 7

byte lastButtonState = LOW;
byte ledState = LOW;

void setup() {
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT);
}

void loop() {
  byte buttonState = digitalRead (BUTTON_PIN);
  if(buttonState != lastButtonState) {
    lastButtonState = buttonState;
    if(buttonState == LOW) {
      ledState = (ledState == HIGH) ? LOW: HIGH;
      digitalWrite(LED_PIN, ledState);
    }
  }
}