void setup() {
  Serial.begin(115200);
  resultat(3, &triple);
  resultat(9, &quadruple);
}

void loop() {
  // put your main code here, to run repeatedly:

}

void resultat(int a, int (*pf)(int))
{
    Serial.println((*pf)(a)) ;
}

int quadruple(int a)
{
  return a * 4;
}

int triple(int a)
{
  return a * 3;
}