/* Note: If it doesn't compile, please try compiling it again. I just got sometimes a compiler error out of nowhere, while at other times, it worked (and I had a pretty big argument with the compiler about it). In Code::Blocks this works perfectly though. Grr. 1. Rule: I only before V and X 2. Rule: X only before L and C 3. Rule: C only before D and M */ // //////////PREPROCESSOR////////// // #include #include #include #include // //////////FUNCTIONS////////// // void showInfo() { std::cout << "\nRoman Number Converter V. 1.0.0\n" "By Naitomea\n\n" "This application allows you to either convert Roman numbers to Arabic Numbers or Arabic numbers to Roman Numbers.\n" "There is also a library provided with each Roman sign's value.\n"; } // //////////STRUCTURES////////// // namespace Convert { //anonymous strcuture holding the key : value pairs struct { int key; std::string value; } Signs[13] = { {1, "I"}, {4, "IV"}, {5, "V"}, {9, "IX"}, {10, "X"}, {40, "XL"}, {50, "L"}, {90, "XC"}, {100, "C"}, {400, "CD"}, {500, "D"}, {900, "CM"}, {1000, "M"} }; bool validateNumber(std::string num) { //first test: only correct characters in the string/ string not empty? std::regex firstCheck("[IVXLCDM]+"); if (!std::regex_match(num, firstCheck)) { //std::cout << "First mask failed!" << std::endl; return false; } //second test: basic/outside structure okay? std::regex secondCheck("^M*([CD]*|CM)([LX]*|XC)([IV]*|IX)$"); if (!std::regex_match(num, secondCheck)) { //std::cout << "Second mask failed!" << std::endl; return false; } //third test: any character except M recurring more than three(two) times? std::regex thirdCheck("I{4,100}|V{2,100}|X{4,100}|L{2,100}|C{4,100}|D{2,100}"); if (std::regex_search(num, thirdCheck)) { //std::cout << "Third mask failed!" << std::endl; return false; } //fourth test: deep/inside structure okay? std::regex fourthCheck("^M*((CM)?|(CD)?|D?C*)((XC)?|(XL)?|L?X*)((IX)?|(IV)?|V?I*)$"); if (!std::regex_match(num, fourthCheck)) { //std::cout << "Fourth mask failed!" << std::endl; return false; } //else: everything clean return true; } std::string ToRoman(int num) { std::string romanNumber {""}; while (num > 0) { for (std::size_t index {12}; index >= 0; --index) { if (num >= Signs[index].key) { romanNumber += Signs[index].value; num -= Signs[index].key; break; } } } return romanNumber; } int ToArabic(std::string num) { if (!validateNumber(num)) { throw "Invalid roman number."; } int arabicNum {0}; std::size_t position {0}; bool match {true}; while (position != std::string::npos && match) { match = false; std::size_t currentPosition {}; std::size_t least_position = num.length() - 1; for (std::size_t index {0}; index < 13; ++index) { if (num.find(Signs[index].value, position) <= least_position) { least_position = num.find(Signs[index].value); currentPosition = index; match = true; } } if (match) { arabicNum += Signs[currentPosition].key; position += (Signs[currentPosition].value).length(); } } return arabicNum; } void showSigns() { for (std::size_t index {0}; index < 13; ++index) { if (Signs[index].value.length() == 1) { std::cout << Signs[index].key << " = " << Signs[index].value << std::endl; } } } } // //////////MAIN FUNCTION////////// // int main() { char mode {}; std::cout << "Welcome!\n"; std::cout << "\nRoman Number Converter ~ Menu\n" "? Convert to (R)oman Number\n" "? Convert to (A)rabic number\n" "? (S)how Roman signs\n" "? Show (I)nfo\n" "? (Q)uit\n"; std::cin >> mode; switch (mode) { case 'r': [[fallthrough]]; case 'R': { int num {}; std::cout << "\nEnter the number to be converted: "; std::cin >> num; if (num <= 0) { std::cerr << "Invalid numeric value, number was set to 1!" << std::endl; num = 1; } else { std::cout << num << std::endl; } std::cout << "The Roman equivalent is: " << Convert::ToRoman(num) << std::endl; } break; case 'a': [[fallthrough]]; case 'A': { std::string num {}; std::cout << "\nEnter the number to be converted: "; std::cin >> num; try { std::cout << num << std::endl; std::cout << "\nThe Arabic equivalent is: " << Convert::ToArabic(num) << std::endl; } catch (const char* msg) { std::cerr << "Error: " << msg; std::cerr << "\nPlease try again." << std::endl; } } break; case 's': [[fallthrough]]; case 'S': { std::cout << "\nRoman signs:\n"; Convert::showSigns(); } break; case 'i': [[fallthrough]]; case 'I': { showInfo(); } break; default: { std::cout << "\nIncorrect input. Please try again." << std::endl; } } return 0; }

Roman Number Converter w/ RegEx