void encode4PlusDigits(int value)
      {
            // slices an int number. eg.
            // a[1,2,3] = a[1] = 2
            int valueLen = to_string(value).length();
            int sliced[valueLen];
            for (int i = 0; i < valueLen; i++)
            {
                  sliced[i] = value % 10;
                  value /= 10;
                  this->data.push_back((sliced[i] * 3) % 10);
            }
            // reverse the vector because i sliced the array the wrong way around
            reverse(this->data.begin(), this->data.end());
      }