// constants won't change
const int BUTTON_PIN = 7; // Arduino pin connected to button's pin
const int LED_PIN    = 3; // Arduino pin connected to LED's pin

// variables will change:
bool ledState = false;        // variable to hold LED state
int lastButtonState = HIGH;   // pullup pin idles HIGH

void setup() {
  Serial.begin(9600);                // initialize serial
  pinMode(BUTTON_PIN, INPUT_PULLUP); // set arduino pin to input pull-up mode
  pinMode(LED_PIN, OUTPUT);          // set arduino pin to output mode
}

void loop() {
  int currentButtonState = digitalRead(BUTTON_PIN); // read the button
  if (lastButtonState != currentButtonState) {      // if it changed
    lastButtonState    = currentButtonState;        // save the state
    if (currentButtonState == LOW)  {               // if LOW was just pressed
      Serial.println("The button was just pressed");
      // toggle state of LED
      ledState = !ledState;
      // control LED arccoding to the toggled state
      digitalWrite(LED_PIN, ledState);
    } else  {                                       // if HIGH was just released
      Serial.println("The button was just released");
    }
    delay(20);  // debounce the button
  }
}