char data;  // create a character variable type
void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);  // baud rate
pinMode(13, OUTPUT); // (pin number , input/output) 
pinMode(10, INPUT);
Serial.print("Hello World");  // to print 
Serial.println("Hello World");  // to print by leaving a line

}

void loop() {
  // put your main code here, to run repeatedly:
digitalWrite(13, HIGH);   //(pin number , HIGH/LOW) used ot turn ON and OFF the LED
delay(1000); // delay in ms (milli seconds)
digitalWrite(13, LOW);   
delay(1000);
Serial.print("Hello World");  // to print multiple times 

// conditional statement
if(Serial.available()>0){
  data =Serial.read();
  // Serial.println(data);
  if(data=='a'){
    Serial.println("Hello!");
  }
    else if(data=='c'){
      Serial.println("Bye");
    }

}
}