schol_roman_numeral.cpp

// Program to convert to roman numerals.
//
// I'm going to split the number into digits, and call a function to
// convert each one to roman numerals individually.

#include <string>
#include <iostream>

using namespace std;

string ConvertDigit(int digit, char one, char five, char ten);

int main() {
    int n;
    cin >> n;

    string s = ConvertDigit((n/1000)%10, 'M', ' ', ' ')
             + ConvertDigit((n/100)%10,  'C', 'D', 'M')
             + ConvertDigit((n/10)%10,   'X', 'L', 'C')
             + ConvertDigit(n%10,        'I', 'V', 'X');

    cout << s << endl;
}

string ConvertDigit(int digit, char one, char five, char ten) {

    // handle 4 and 9;
    if (digit == 4) {
        return string() + one + five;
    }
    if (digit == 9) {
        return string() + one + ten;
    }

    string res;

    // treat 0-3 and 5-8 cases as the same.
    if (digit >= 5) {
        res += five;
        digit -= 5;
    }

    // append the correct number of ones.
    for (int i = 0; i < digit; i++) {
        res += one;
    }
    return res;
}