// constants won't change. They're used here to set pin numbers:
const int buttonPin = 2;    // the number of the pushbutton pin
const int ledPin = 3;       // the number of the LED pin

// Variables will change:
int ledState = LOW;         // the current state of the output pin
int buttonState;            // the current reading from the input pin
int lastButtonState = LOW;  // the previous reading from the input pin

void setup() {
  // put your setup code here, to run once:
 pinMode(buttonPin, INPUT);
  pinMode(ledPin, OUTPUT);

  // set initial LED state
  digitalWrite(ledPin, ledState);
}

void loop() {
  // put your main code here, to run repeatedly:
// read the state of the switch into a local variable:
  int reading = digitalRead(buttonPin);

  // if the button state has changed:
  if (reading != lastButtonState) {
    // update the button state
    buttonState = reading;

    // only toggle the LED if the new button state is HIGH
    if (buttonState == HIGH) {
      ledState = !ledState;
    }
  }

  // set the LED:
  digitalWrite(ledPin, ledState);

  // save the reading. Next time through the loop, it'll be the lastButtonState:
  lastButtonState = reading;
}