const int led_pin = 9;
const int button_pin = 5;

int led_state = LOW;

void setup() {
  // put your setup code here, to run once:
  pinMode(led_pin, OUTPUT);
  pinMode(button_pin, INPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  if(digitalRead(button_pin) == LOW and led_state == LOW){
    led_state = HIGH;
    digitalWrite(led_pin, HIGH);
  }
  
  if(digitalRead(button_pin) == LOW and led_state == HIGH){
    led_state = LOW;
    digitalWrite(led_pin, LOW);
  }
}