const byte pin_LED=13;
const byte pin_Btn=2;
byte prev_val_Btn=HIGH;
byte ledstate=HIGH;
void setup() {
  // put your setup code here, to run once:
  pinMode(pin_Btn, INPUT_PULLUP);
  pinMode(pin_LED, OUTPUT);
  digitalWrite(pin_LED,ledstate);
}
void loop() {
  // put your main code here, to run repeatedly:
  byte actu_val_Btn=digitalRead(pin_Btn);
  if ((prev_val_Btn==HIGH) && (actu_val_Btn==LOW))
 {
  ledstate=!ledstate;
  digitalWrite(pin_LED,ledstate);
 }
 prev_val_Btn=actu_val_Btn;
}