int in = 0;
int ledPin = 13;
int st=LOW;
int sensorPin=A0;
int sensorValue=0;
const char* msg="";

void setup()
{
   Serial.begin(115200);	// opens serial port, sets data rate to 9600 bps
   pinMode(ledPin,OUTPUT);
}

void loop() 
{
   delay(100);
   
   // sensorValue = analogRead( sensorPin );
   // Serial.println( sensorValue, DEC );
   
   // send data only when you receive data:
   if( Serial.available() > 0 ) 
   {
      // read the incoming byte:
      msg="";
      in = Serial.read();
      if( in == 49 )
      {
         st=LOW;
         msg="It's low!";
      }
      
      if( in == 50 )
      {
         st=HIGH;
         msg="It's high!";
      }

      // say what you got:
      //	Serial.print("I received: ");
      //	Serial.println(incomingByte, DEC);
      if( *msg )
      {
         digitalWrite(ledPin,st);         
         Serial.println(msg);
      }
      delay( 100 );
   }
}