NumToStr strintToNum

#include <iostream>
#include <cstdlib>
#include <string>
using std::cout;
using std::cin;
using std::endl;
using std::string;

int convertToNum(char c);
char convertToChar(int i);
int cal_gap(int a_i, int b_i);
string numberToString(int gap);

int main(){

    while(1){

        string a_s, b_s;
        int a_i = 0, b_i = 0;

        cin >> a_s;
        if (a_s == "#") {
            break;
        }// get out point
        cin >> b_s;

// convert string to number
        for(int i = 0; a_s[i] != '\0'; i++){
            //a_i += convertToNum(a_s[i]);
            if (convertToNum(a_s[i]) >= convertToNum(a_s[i+1])){
                a_i += convertToNum(a_s[i]);
            }else{
                a_i -= convertToNum(a_s[i]);
            }
        }
        for(int i = 0; b_s[i] != '\0'; i++){
            if (convertToNum(b_s[i]) >= convertToNum(b_s[i+1])){
                b_i += convertToNum(b_s[i]);
            }else{
                b_i -= convertToNum(b_s[i]);
            }
        }

    //  cout << "a_i: " << a_i << endl; // debugging
    //  cout << "b_i: " << b_i << endl; //debugging

// calculate the gap between two numbers
        int gap = cal_gap(a_i,b_i);
    //  cout << "gap: "<< gap << endl; // debugging
        if (gap == 0){
            cout << "ZERO" << endl;
            continue;
        }else{
            string ans;
            ans = numberToString(gap);
            cout << ans << endl;
        }// end of if
    }// end of while


}// end of main

string numberToString(int gap){
    string stringTmp;
    switch(gap/1000){
        case 0:
            break;
        case 1:
            stringTmp += "M";
            break;
        case 2:
            stringTmp += "MM";
            break;
        case 3:
            stringTmp += "MMM";
            break;
    }

    switch(gap%1000/100){
        case 9:
            stringTmp += "CM";
            break;
        case 8:
            stringTmp += "DCCC";
            break;
        case 7:
            stringTmp += "DCC";
            break;
        case 6:
            stringTmp += "DC";
            break;
        case 5:
            stringTmp += "D";
            break;
        case 4:
            stringTmp += "CD";
            break;
        case 3:
            stringTmp += "CCC";
            break;
        case 2:
            stringTmp += "CC";
            break;
        case 1:
            stringTmp += "C";
            break;


    }

    switch(gap%1000%100/10){
        case 9:
            stringTmp += "XC";
            break;
        case 8:
            stringTmp += "LXXX";
            break;
        case 7:
            stringTmp += "LXX";
            break;
        case 6:
            stringTmp += "LX";
            break;
        case 5:
            stringTmp += "L";
            break;
        case 4:
            stringTmp += "XL";
            break;
        case 3:
            stringTmp += "XXX";
            break;
        case 2:
            stringTmp += "XX";
            break;
        case 1:
            stringTmp += "X";
            break;
    }
    switch(gap%1000%100%10/1){
        case 9:
            stringTmp += "IX";
            break;
        case 8:
            stringTmp += "VIII";
            break;
        case 7:
            stringTmp += "VII";
            break;
        case 6:
            stringTmp += "VI";
            break;
        case 5:
            stringTmp += "V";
            break;
        case 4:
            stringTmp += "IV";
            break;
        case 3:
            stringTmp += "III";
            break;
        case 2:
            stringTmp += "II";
            break;
        case 1:
            stringTmp += "I";
            break;
    }

    return stringTmp;
}


int convertToNum(char c){
    switch(c){
    case 'I':
       return 1;
       break; //optional
    case 'V':
       return 5;
       break; //optional
    case 'X':
       return 10;
       break; //optional
    case 'L':
       return 50;
       break; //optional
    case 'C':
       return 100;
       break; //optional
    case 'D':
       return 500;
       break; //optional
    case 'M':
       return 1000;
       break; //optional
    }// end of switch

}


int cal_gap(int a_i, int b_i){
    return abs((a_i - b_i));
}