bool numberDefined;
int second;

void setup() {
  pinMode(0, INPUT);
  pinMode(1, OUTPUT);
  Serial.begin(9600);
  numberDefined = false;
  second = 0;
}

void loop() {
  if (Serial.available()) {
    int var = Serial.read();
    int val = var - 0x30;
    if (val >= 0 && val < 9) {
      Serial.print("LED will glow ");
      Serial.print(val);
      Serial.println(" seconds.");
      second = val;
      numberDefined = true;
    }
  }
  
  int state = digitalRead(0);

  if (state == LOW) {
    if (numberDefined == true) {
      Serial.println("Button Pressed");
      digitalWrite(1, HIGH);
      delay(1000 * second);
      digitalWrite(1, LOW);
      delay(100);
      numberDefined = false;
      Serial.println("You can set another time");
    } else {
      Serial.println("Glow time is not defined");
      delay(1000);
    }
  } else
    digitalWrite(1, LOW);
}