const byte PinLed = 10;
const byte PinBut = 3;

// setup is run once at startup
void setup() {
    pinMode (PinLed, OUTPUT);

    //INPUT_PULLUP enables interval resistor tied HIGH
    pinMode (PinBut, INPUT_PULLUP);
}

// loop is run repeatedly
void loop() {
    // check if button grounds pin, making it LOW
    if (LOW == digitalRead (PinBut))
      digitalWrite (PinLed, HIGH);  // turn on
    // other wise, pin is HIGH
    else
      digitalWrite (PinLed, LOW);   // turn off
}