Find the Difference

using System;
using System.Collections.Generic;

namespace leetcodecsharp
{
    class Program
    {

        private static char FindTheDifference(string s, string t)
        {
            // turn string into int then do minus.
            int s_arr_sum = 0;
            char[] s_arr = s.ToCharArray();
            for (int i = 0; i < s.Length; i++)
            {
                s_arr_sum += char.ToUpper(s_arr[i]);
            }
            int t_arr_sum = 0;
            char[] t_arr = t.ToCharArray();
            for (int i = 0; i < t.Length; i++)
            {
                t_arr_sum += char.ToUpper(t_arr[i]);
            }
            return char.ToLower((char)(t_arr_sum - s_arr_sum));
        }

        //public static string GenerateRandom(int total)
        //{
        //    var chars = "abcdefghijklmnopqrstuvwxyz";
        //    var stringChars = new char[total];
        //    var random = new Random();

        //    for (int i = 0; i < stringChars.Length; i++)
        //    {
        //        stringChars[i] = chars[random.Next(chars.Length)];
        //    }

        //    var finalString = new String(stringChars);
        //    return finalString;
        //}
        public static void Main(string[] args)
        {
            string s = "abcde";
            // String t is generated by random shuffling string s
            // and then add one more letter at a random position.
            string t = "bgaedc";
            Console.WriteLine(FindTheDifference(s, t));
        }
    }
}