unsigned long romanToNumber(const char* roman) {
  unsigned long result = 0;
  int prevValue = 0;

  for (int i = strlen(roman) - 1; i >= 0; --i) {
    int value = 0;
    switch (roman[i]) {
      case 'I': value = 1; break;
      case 'V': value = 5; break;
      case 'X': value = 10; break;
      case 'L': value = 50; break;
      case 'C': value = 100; break;
      case 'D': value = 500; break;
      case 'M': value = 1000; break;
    }

    if (value < prevValue) result -= value;
    else result += value;

    prevValue = value;
  }

  return result;
}

void printRomanNumeral(unsigned long num) {
  const unsigned long values[] = {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
  const char* numerals[] = {"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"};

  for (int i = 0; num > 0; ++i) {
    while (num >= values[i]) {
      Serial.print(numerals[i]);
      num -= values[i];
    }
  }
}


void setup() {
  Serial.begin(115200);

  const char* romanNumeral = "MMMMDLXVII";
  unsigned long convertedNumber = romanToNumber(romanNumeral);
  Serial.print(romanNumeral); Serial.print(" ==> "); Serial.println(convertedNumber);
  Serial.print(convertedNumber); Serial.print(" ==> "); printRomanNumeral(convertedNumber);
}

void loop() {}