Roman to decimal and decimal to roman number converter

r2d_d2r_converter.cpp

#include <iostream> 
#include <cctype>
#include <array>
#include <unordered_map>
using namespace std; 

static unordered_map<char, int> roman_to_dec {
	{'I', 1},
	{'V', 5},
	{'X', 10},
	{'L', 50},
	{'C', 100},
	{'D', 500},
	{'M', 1000}
};

static unordered_map<int, string> dec_to_roman {
	{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"}
};

int roman_decimal(string roman)
{
	int dec{0};
	int prev{0};
	for(auto it = roman.rbegin(); it != roman.rend(); ++it)
	{
		int curr = roman_to_dec[toupper(*it)];
		
		if(curr < prev) dec -= curr;
		else dec += curr;
		
		prev = curr;
	}
	cout << roman << ": " << dec << '\n';
	return dec;
}

string decimal_roman(int k)
{
	int copy_of_k = k;
	string roman {};
	
	array<int, 13> mapped_num {1, 4, 5, 9, 10, 40, 50, 90, 100, 400, 500, 900, 1000};
	
	while(k > 0)
	{
		int max = 0;
		for(int &i: mapped_num)
		{
			if(i > k) break;
			max = i;
		}
		
		roman += dec_to_roman[max];
		k -= max;
	}
	
	cout << copy_of_k << ": " << roman << '\n';
	return roman;
}

int main () 
{
	int k = 1203;
	string roman_str = decimal_roman(k);
	roman_decimal(roman_str);
	
	return 0; 
}