<pre name="code" class="cpp">using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ceshi3
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("請輸入第一個加數");
            string one = Console.ReadLine();
            Console.WriteLine("請輸入第er個加數");
            string two = Console.ReadLine();

            string res = BigAdd(one, two);
            //Console.WriteLine(res);
            foreach (var item in res)
            {
                Console.WriteLine(item);
            }
        }

        static string BigAdd(string a, string b)
        {
            int k = 0;
            List<int> array = new List<int>();
            List<int> one = new List<int>();
            List<int> two = new List<int>();
            //for (int i = 0; i < a.Length; i++)
            //{
            //    one.Add(int.Parse(a[i].ToString()));
            //}
            //for (int i = 0; i < b.Length; i++)
            //{
            //    two.Add(int.Parse(b[i].ToString()));
            //}
            for (int i = 0; i < (a.Length > b.Length ? a.Length : b.Length); i++)
            {
                if (i >= b.Length)
                    //two.Add(0);
 		    two.Insert(i - b.Length, 0);
                else
                    two.Add(int.Parse(b[i].ToString()));
                if (i >= a.Length)
                    one.Add(0);
                else
                    one.Add(int.Parse(a[i].ToString()));
                
            }

            for (int j = 0; j <= (a.Length > b.Length ? a.Length : b.Length); j++)
            {
                array.Add(0);
            }
            for (int i = (a.Length > b.Length ? a.Length : b.Length) - 1; i >= 0; i--)
            {
                array[i + 1] += (one[i] + two[i])% 10;
                k = (one[i] + two[i])/ 10;

                array[i] += k;
            }
            if (k == 0)
            {
                array.RemoveAt(0);
            }
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < array.Count; i++)
            {
                sb.Append(array[i]);
            }
            string s = sb.ToString();
            //Console.WriteLine(s);
            return s;

        }
    }
  
}