#define led 7
int a = 0;

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

void loop() {
  if(Serial.available() != 0){ 
    a= Serial.read(); 
 }

 if (a== '0') {
  digitalWrite(ledPin, LOW);
 }
 else if (a== '1') {
  digitalWrite(ledPin, HIGH);
 } 
}