乘法

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication1
{
    class Multiply
    {
        private int len1, len2;
        private int[] result;

        public string Result
        {
            get
            {
                StringBuilder sbResult = new StringBuilder();
                int lable = 0;
                if (result[0] == 0)
                {
                    lable = 1;
                }

                for (; lable < result.Length; lable++)
                {
                    sbResult.Append(result[lable]);
                }
                return sbResult.ToString();
            }
        }

        public Multiply(string str1, string str2)
        {
            len1 = str1.Trim().Length;
            len2 = str2.Trim().Length;
            int num1, num2, num3;
            int len = len1 + len2;
            result = new int[len];

            for (int i = len1; i > 0; i--)
            {
                for (int j = len2; j > 0; j--)
                {
                    num1 = Convert.ToInt32(str1[i - 1].ToString());
                    num2 = Convert.ToInt32(str2[j - 1].ToString());
                    num3 = num1 * num2;
                    SumUp(i, j, num3.ToString(), num3.ToString().Length);
                }
            }
        }

        private void SumUp(int i, int j, string num, int len)
        {
            for (int k = 0; k < len; k++)
            {
                Carry((i + j - k), Convert.ToInt32(num[len - k - 1].ToString()));
            }
        }

        private void Carry(int s, int v)
        {
            int vv;
 
            vv = result[s - 1] + v;

            if (vv > 10)
            {
                result[s - 1] = vv % 10;
                Carry(s - 1, vv / 10);
            }
            else
            {
                result[s - 1] = vv;
            }
        }
    }
}