// code uses a single if (Serial.available()>0) {...}

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  Serial.println("Hello, ESP32!");

  Serial.print("buffer empty: ");
  Serial.println(Serial.read());  // buffer empty - prints -1
  
}

void loop() {
  if (Serial.available() > 0) {
    char ch = Serial.read();  // ch only available in if statement
    Serial.print("Received ");
    Serial.write(ch);
    Serial.print(" which is ");
    Serial.println(ch, DEC);
}
  delay(1000);
}