char bilgi;

void setup()
{
  pinMode(13, OUTPUT);
  pinMode(12, OUTPUT);
  Serial.begin(9600);
}

void loop()
{
  if(Serial.available()) 
  {
    bilgi=Serial.read();
    if(bilgi=='a')
    digitalWrite(13,HIGH);

    if(bilgi=='b')
    digitalWrite(13,LOW);

    if(bilgi=='g')
    digitalWrite(12,HIGH);

    if(bilgi=='c')
    digitalWrite(12,LOW);
  }
}