◆ BUTTON을 누르면 HIGH가 되고, LED도 HIGH가 되기 때문에 불이 들어 온다
◆ 누르면 "Button was pressed !!", 안누르면 "Button was NOT pressed !!" 가 출력 된다.

>>>  switch_led.c  <<<<<<<<<<<<<<
#include <stdio.h>
#include <stdlib.h>
#include <wiringPi.h>
#include <unistd.h>
#define BUTTON 2 //27
#define LED 0 //17
int main(void)
{
    if(wiringPiSetup()==-1)
  return -1;
pinMode(BUTTON,INPUT);
pinMode(LED, OUTPUT);
while(1)
{
if(digitalRead(BUTTON)==HIGH){
printf("Button was pressed !! \n");
digitalWrite(LED,HIGH);
} else {
printf("Button was NOT pressed !! \n");
digitalWrite(LED,LOW);
}
sleep(1);
}
return 0;
}
----------------------------------------------------------
$ gcc  -o  switch_led  switch_led.c  -lwiringPi
$ sudo  ./switch_led