#define ledA 13
#define ledB 12
#define ledC 11

void setup() {
  // put your setup code here, to run once:
 pinMode (ledA, OUTPUT);
 pinMode (ledB, OUTPUT);
 pinMode (ledC, OUTPUT);
 Serial.begin(9600);
 Serial.setTimeout(10);
 Serial.println ("print");
}

void loop() {
  // put your main code here, to run repeatedly:
 while (Serial.available() > 0){
  String str = Serial.readString();
  str.trim();

  if (str == "a"){
    digitalWrite (ledA, HIGH);
    digitalWrite (ledB, LOW);
    digitalWrite (ledC, LOW);
    Serial.println ("ledA is ON");
  }
  else if (str == "b") {
    digitalWrite (ledA, LOW);
    digitalWrite (ledB, HIGH);
    digitalWrite (ledC, LOW);
    Serial.println ("ledB is ON");
  }
  else if (str == "c"){
    digitalWrite (ledA, LOW);
    digitalWrite (ledB, LOW);
    digitalWrite (ledC, HIGH);
    Serial.println ("ledC is ON");
  }
  else {
    digitalWrite (ledA, LOW);
    digitalWrite (ledB, LOW);
    digitalWrite (ledC, LOW); 
    Serial.println ("pls input a, b, or c");
  }
 }
}