void setup() {
  Serial.begin(9600);
}

void loop() {
  if(Serial.available() > 0){
    switch(Serial.read()){
      case '1':
        Serial.println("You have pressed one");
        break;
      case '2':
        Serial.println("You have pressed two");
        break;
      case '3':
        Serial.println("You have pressed three");
        break;
     default:
        Serial.println("Try sending numbers like 1 or 2 or 3..");
        break;
    }//end switch case
  }//end if
}//end loop