c# - Converting integers to roman numerals

Question

I'm trying to write a function that converts numbers to roman numerals. This is my code so far; however, it only works with numbers that are less than 400. Is there a quick and easy way to do this conversion, or extend my existing code so that it handles all cases? Thanks in advance for any help.

static string convertroman(int number)
    {
        int l = number / 10;
        StringBuilder sb = new StringBuilder();
        for (int m = 0; m <= l; m++)
        {
            if (l == 0)
            {
                break;
            }
            if (l == 5)
            {
                sb = sb.Append(ro.L.ToString());
                break;
            }
            if (l == 4)
            {
                sb = sb.Append(ro.X.ToString()).Append(ro.L.ToString());
                break;
            }
            if (l == 9)
            {
                sb = sb.Append(ro.X.ToString()).Append(ro.C.ToString());
                break;
            }
            if (l == 10)
            {
                sb = sb.Append(ro.C.ToString());
                break;
            }

            if (l > 5 && l < 9)
            {
                sb = sb.Append(ro.L.ToString());
                l = l - 5;
                m = 0;
                // break;
                continue;
            }
            if (l > 10)
            {
                sb = sb.Append(ro.C.ToString());
                l = l - 10;
                m = 0;
                // continue;

            }
            else
            {
                sb = sb.Append(ro.X.ToString());
            }

        }
        int z = number % 10;
        for (int x = 0; x <= z; x++)
        {
            if (z == 0)
            {
                break;
            }
            if (z == 5)
            {
                sb = sb.Append(ro.V.ToString());
                break;
            }
            if (z == 4)
            {
                sb = sb.Append(ro.I.ToString()).Append(ro.V.ToString());
                break;
            }
            if (z == 9)
            {
                sb = sb.Append(ro.I.ToString()).Append(ro.X.ToString());
                break;
            }
            if (z == 10)
            {
                sb = sb.Append(ro.X.ToString());
                break;
            }
            if (z > 5 && z < 9)
            {
                sb = sb.Append(ro.V.ToString());
                z = z - 5;
                x = 0;
            }
            else
            {
                sb.Append(ro.I.ToString());
            }              

        }
        return sb.ToString();           
    }

Answer 1

Try this, simple and compact:

public static string ToRoman(int number)
{
    if ((number < 0) || (number > 3999)) throw new ArgumentOutOfRangeException("insert value betwheen 1 and 3999");
    if (number < 1) return string.Empty;            
    if (number >= 1000) return "M" + ToRoman(number - 1000);
    if (number >= 900) return "CM" + ToRoman(number - 900); 
    if (number >= 500) return "D" + ToRoman(number - 500);
    if (number >= 400) return "CD" + ToRoman(number - 400);
    if (number >= 100) return "C" + ToRoman(number - 100);            
    if (number >= 90) return "XC" + ToRoman(number - 90);
    if (number >= 50) return "L" + ToRoman(number - 50);
    if (number >= 40) return "XL" + ToRoman(number - 40);
    if (number >= 10) return "X" + ToRoman(number - 10);
    if (number >= 9) return "IX" + ToRoman(number - 9);
    if (number >= 5) return "V" + ToRoman(number - 5);
    if (number >= 4) return "IV" + ToRoman(number - 4);
    if (number >= 1) return "I" + ToRoman(number - 1);
    throw new ArgumentOutOfRangeException("something bad happened");
}