Download roman.cpp

#include <iostream>
#include <string>
#include <vector>

//
// macro to give the size of an array
//
#define ARRAY_SIZE(array) (sizeof(array)/sizeof(array[0]))

//
// roman - convert a number to roman numerals
//
// value:	unsigned int	: the number to convert, range: 1..3999 inclusive
// return:	std::string		: string containing the roman numerals
//
std::string roman (unsigned int value)
{
    // The Romans didn't have a numeral for zero
    if (value == 0) throw std::out_of_range("roman: value == 0");

    // This function is specified to support value up to 3999 only
    if (value > 3999) throw std::out_of_range("roman: value > 3999");

    // string to conatain the roman numerals
    std::string romanized;

    // strings to contain the characters used for digits 1..9 for the current power of 10.
    std::string I, V, X;

    // the roman numerals for 1 and 5 in ascending order of powers of 10
    // last two elements are ? to avoid out of bounds exception when using M as 1
    const char numeraldata[] = {'I', 'V', 'X', 'L', 'C', 'D', 'M', '?', '?'};
    // use the p, p+size constructor for the vector to safely handle the above data
    std::vector<char> numerals (numeraldata, numeraldata + ARRAY_SIZE(numeraldata));

    // an index into the above array
    unsigned int index = 0;

    // the maximum index into the numerals array
    // -2 because of zero based index + null at end of string
    const size_t maxindex = (sizeof(numerals)/sizeof(numerals[0])) - 2;

    // for each power of 10 (1, 10, 100, 1000, etc)
    for (unsigned int i = value; i > 0; i /= 10)
    {
        // get the current representation for the I,V,X pattern
        I = numerals.at(index++);
        V = numerals.at(index++);
        X = numerals.at(index); // not index++ because current X is reused for the representation of I next time around

        // generate the 0..9 I,V,X roman numeral pattern for the current power of 10
        // and prepend it to the numerals already generated for lower powers of 10
        switch (i % 10) {
            case 0: // romans have no zero representation in their numerals.
                break;
            case 1: // I
                romanized = I + romanized;
                break;
            case 2: // II
                romanized = I + I + romanized;
                break;
            case 3: // III
                romanized = I + I + I + romanized;
                break;
            case 4: // IV
                romanized = I + V + romanized;
                break;
            case 5: // V
                romanized = V + romanized;
                break;
            case 6: // VI
                romanized = V + I + romanized;
                break;
            case 7: // VII
                romanized = V + I + I + romanized;
                break;
            case 8: // VIII
                romanized = V + I + I + I + romanized;
                break;
            case 9: // IX
                romanized = I + X + romanized;
                break;
            default:
                break;
        }
    }
    // return the full string of roman numerals
    return romanized;
}

//
// generate the result for the full range
// in the same output format as the reference file, so I can diff it.
//
int main(int argc, char* argv[])
{
    try {

        std::cout << std::endl;
        for (int i = 1; i <= 3999; ++i)
        {
            std::cout << i << '\t' << roman (i) << std::endl;
        }

    } catch (std::out_of_range &e) {
        std::cerr << "Exception: " << e.what() << std::endl;
        return EXIT_FAILURE;

    } catch (...) {
        std::cerr << "Exception: Unknown Exception" << std::endl;
    }

    return EXIT_SUCCESS;
}