Roman/Arabic Numeral Converter

using System;

class MainClass {
    static int arabic(string rom)//converts roman numerals to arabic
    {
        int res = 0;
        for(int i =0; i < rom.Length; i++)
        {
            {
                if(rom[i].Equals('i')||rom[i].Equals('I'))
                {
                    if(i == rom.Length-1)
                        ++res;
                    else if(rom[i+1].Equals('i')||rom[i+1].Equals('I'))
                        ++res;
                    else
                        --res;
                }
                if(rom[i].Equals('v')||rom[i].Equals('V'))
                {
                    if(i == rom.Length-1)
                        res+=5;
                    else if(rom[i+1].Equals('i')||rom[i+1].Equals('I')||rom[i+1].Equals('v')||rom[i+1].Equals('V'))
                        res+=5;
                    else
                        res-=5;
                }
                if(rom[i].Equals('x')||rom[i].Equals('X'))
                {
                    if(i == rom.Length-1)
                        res+=10;
                    else if(rom[i+1].Equals('i')||rom[i+1].Equals('I')||rom[i+1].Equals('v')||rom[i+1].Equals('V')||rom[i+1].Equals('x')||rom[i+1].Equals('X'))
                        res+=10;
                    else
                        res-=10;
                }
                if(rom[i].Equals('l')||rom[i].Equals('L'))
                {
                    if(i == rom.Length-1)
                        res+=50;
                    else if(rom[i+1].Equals('i')||rom[i+1].Equals('I')||rom[i+1].Equals('v')||rom[i+1].Equals('V')||rom[i+1].Equals('x')||rom[i+1].Equals('X')||rom[i+1].Equals('l')||rom[i+1].Equals('L'))
                        res+=50;
                    else
                        res-=50;
                }
                if(rom[i].Equals('c')||rom[i].Equals('C'))
                {
                    if(i == rom.Length-1)
                        res+=100;
                    else if(rom[i+1].Equals('i')||rom[i+1].Equals('I')||rom[i+1].Equals('v')||rom[i+1].Equals('V')||rom[i+1].Equals('x')||rom[i+1].Equals('X')||rom[i+1].Equals('l')||rom[i+1].Equals('L')||rom[i+1].Equals('c')||rom[i+1].Equals('C'))
                        res+=100;
                    else
                        res-=100;
                }
                if(rom[i].Equals('d')||rom[i].Equals('D'))
                {
                    if(i == rom.Length-1)
                        res+=500;
                    else if(rom[i+1].Equals('i')||rom[i+1].Equals('I')||rom[i+1].Equals('v')||rom[i+1].Equals('V')||rom[i+1].Equals('x')||rom[i+1].Equals('X')||rom[i+1].Equals('l')||rom[i+1].Equals('L')||rom[i+1].Equals('c')||rom[i+1].Equals('C')||rom[i+1].Equals('d')||rom[i+1].Equals('D'))
                        res+=500;
                    else
                        res-=500;
                }
                if(rom[i].Equals('m')||rom[i].Equals('M'))
                {
                    if(i == rom.Length-1)
                        res+=1000;
                    else if(rom[i+1].Equals('i')||rom[i+1].Equals('I')||rom[i+1].Equals('v')||rom[i+1].Equals('V')||rom[i+1].Equals('x')||rom[i+1].Equals('X')||rom[i+1].Equals('l')||rom[i+1].Equals('L')||rom[i+1].Equals('c')||rom[i+1].Equals('C')||rom[i+1].Equals('d')||rom[i+1].Equals('D')||rom[i+1].Equals('m')||rom[i+1].Equals('M'))
                        res+=1000;
                    else
                        res-=1000;
                }
            }
        }
        return res;
    }
    static string roman(int arab)//converts arabic numerals to roman
    {
        string rom = "";
        while(arab!=0)
        {
            if(arab-1000>=0)
            {
                rom = rom.Insert(rom.Length,"M");
                arab-=1000;
            }
            else if(Math.Abs(arab-900)<=100&&arab>799)
            {
                rom = rom.Insert(rom.Length,"CM");
                arab-=900;
            }
            else if(arab-500>=0)
            {
                rom = rom.Insert(rom.Length,"D");
                arab-=500;
            }
            else if(Math.Abs(arab-400)<=100&&arab>299)
            {
                rom = rom.Insert(rom.Length,"CD");
                arab-=400;
            }
            else if(arab-100>=0)
            {
                rom = rom.Insert(rom.Length,"C");
                arab-=100;
            }
            else if(Math.Abs(arab-90)<=10&&arab>79)
            {
                rom = rom.Insert(rom.Length,"XC");
                arab-=90;
            }
            else if(arab-50>=0)
            {
                rom = rom.Insert(rom.Length,"L");
                arab-=50;
            }
            else if(Math.Abs(arab-40)<=10&&arab>39)
            {
                rom = rom.Insert(rom.Length,"XL");
                arab-=40;
            }
            else if(arab-10>=0)
            {
                rom = rom.Insert(rom.Length,"X");
                arab-=10;
            }
            else if(Math.Abs(arab-9)<=1&&arab!=8)
            {
                rom = rom.Insert(rom.Length,"IX");
                arab-=9;
            }
            else if(arab-5>=0)
            {
                rom = rom.Insert(rom.Length,"V");
                arab-=5;
            }
            else if(Math.Abs(arab-4)<=1&&arab!=3)
            {
                rom = rom.Insert(rom.Length,"IV");
                arab-=4;
            }
            else if(arab-1>=0)
            {
                rom = rom.Insert(rom.Length,"I");
                arab-=1;
            }
            //arab = 0;
        }
        return rom;
    }
    static void Main()
    {
        bool y = true;
        Console.Write("input: ");
        string s = Console.ReadLine();
        Console.Write(s + "\noutput: ");
        for(int i = 0; i < 10; i++)
        {
            if(s.IndexOf(Convert.ToString(i)) != -1)//if ints are detected in the string it is put through the roman converter
            {
                Console.WriteLine(roman(Convert.ToInt32(s)));
                y = false;
                break;
            }
        }
        if (y == true)//if no ints are detected in the string it is put through the arabic converter
        {
            Console.Write(arabic(s));
        }
    }
}