break;
      case '"':
        string();

    }
  }
  private void string() {
    while (peek() != '"' && !isAtEnd()) {
      if (peek() == '\n')
        line++;
      advance();
    }
    if (isAtEnd()) {
      Lox.error(line, "Unterminated string.");
      return;

    // The closing ".
    advance();
    // Trim the surrounding quotes.
    String value = source.substring(start + 1, current - 1);
    addToken(STRING, value);