int knop = 9;        
int led = 11;      

int status = HIGH;      
int Input;         
int vorigeInput = LOW;   

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

void loop(){
  // put your main code here, to run repeatedly:
  Input = digitalRead(knop);
  if (Input == HIGH && vorigeInput == LOW)
  {
    if (status == HIGH)
      status = LOW;
    else
      status = HIGH;

  }

  digitalWrite(led, status);

  vorigeInput = Input;
}