Arduinoを始めよう　第二版　Massimo Banzi O'REILLY　p.41

SWITCH_LED.ino

const int LED = 12; 
const int BUTTON = 7;

int val = 0;
int old_val = 0;
int state = 0;

void setup() {
        pinMode(LED, OUTPUT);
        pinMode(BUTTON, INPUT);
}

void loop() {
        val = digitalRead(BUTTON);

        if ((val == HIGH) && (old_val == LOW)) {
                state = 1 - state;
                delay(10);
        }   

        old_val = val;

        if (state == 1) {
        digitalWrite(LED, HIGH);
        } else {
        digitalWrite(LED, LOW);
        }   
}