/* Push-button and LED

Circuit Connections:
PIN_0 => LED_Anode - LED_Cathode = > Resistor 220Ω => Gnd
PIN_4 => Pull-up resistor (built in) => push-button (Gnd)
*/

#define led_pin 0    //give the name “led_pin” to PIN_0
#define pb_pin 4    //give the name “pb_pin” to PIN_4

//The setup() function initializes and sets the initial values
//It will only run once after each powerup or reset
void setup()
{
  //Configure PIN_0 to behave as outputs
  pinMode(led_pin, OUTPUT);
  //Configure PIN_4 to behave as input with activated pull-up resistor
  pinMode(pb_pin, INPUT_PULLUP);
}

//This function loops consecutively
void loop() {
  //The LED follows the state of push-button
  digitalWrite(led_pin, digitalRead(pb_pin));  
}