/*
  Button_LED
 
 Turns on and off a light emitting diode(LED) connected to digital  
 pin 13, when pressing a pushbutton attached to pin 7. 
 
 The circuit:
 LED attached from pin 13 to ground 
 pushbutton attached to pin 4 from ground
 
 */

int buttonPin = 4;     // the number of the pushbutton pin
int ledPin =  13;      // the number of the LED pin

int buttonState;         // variable for reading the pushbutton status

void setup() {

  pinMode(ledPin, OUTPUT);   // initialize the LED pin as an output:     

  pinMode(buttonPin, INPUT);    // initialize the pushbutton pin as an input:
 
  digitalWrite (buttonPin, HIGH);  // eliminates the need for a pull down resistor by giving a default state.
}

void loop(){
 
  buttonState = digitalRead(buttonPin); // read the state of the pushbutton value:

 
   // check if the pushbutton is pressed.
  if (buttonState == HIGH) {     // if it is, the buttonState is HIGH:
      digitalWrite(ledPin, HIGH);  // turn LED on:    
  } else {
     digitalWrite(ledPin, LOW); // turn LED off:
  }
}