// 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 = 13;    // the number of the LED pin
// variables will change:
int buttonState = 0;  // variable for reading the pushbutton status 
void setup() {
  // initialize the LED pin as an output: 
  pinMode(ledPin, OUTPUT);
  // initialize the pushbutton pin as an input: 
  pinMode(buttonPin, INPUT);
}
void loop() {
  // read the state of the pushbutton value: 
  buttonState = digitalRead(buttonPin);
  // check if the pushbutton is pressed. If it is, the buttonState is HIGH: 
  if (buttonState == HIGH) {
  // turn LED on: 
  digitalWrite(ledPin, HIGH); 
  } else {
  // turn LED off: 
  digitalWrite(ledPin, LOW); 
  }
}