public void print() {
    // prints the BigInt as a integer
    int len = this.length();
    if(len == 0) {
      System.out.println("0");
      return;
    }
    for(int i = len - 1; i >= 0; i--) {
      String zfill = "";
      for(int j = power_ - 1; j > 0; j--) {
        if(getDigit(i).value() < (long)Math.pow(10, j)) {
          if(i < len - 1)
            zfill += "0";
        }
        else break;
      }
      System.out.print(zfill + getDigit(i).value());
    }
    System.out.print("\n");
  }