const int LED = 9;     // define the pin associated to LED
const int BUTTON = 7;  // define the pin associated to BUTTON
int state_actual,state_old,light; // define some variables

// Initialization
void setup() {
pinMode(LED, OUTPUT);
pinMode(BUTTON, INPUT);
light=0;
}

void loop() {
  state_actual=digitalRead(BUTTON);
  
  // if the state rise from 0 to 1 the light variable toggle
  if ((state_actual-state_old)==1) {light=1-light;} 
  digitalWrite(LED, light);
  
  state_old=state_actual; // update the state
  // delay (100);            // uncomment this line to avoid undesired commutation
}