C#版 大数计算器加法

///
 

   /// 基类,抽象类,定义常用方法
    ///
    abstract class BigCalculate
    {
        public abstract string Oper(string num1, string num2);

        //反转数字顺序
        protected string InvertOrder(string str)
        {
            char[] chTemp = new char[str.Length];

            for (int i = 0; i < str.Length; i++)
            {
                chTemp[i] = str[str.Length - i-1];
            }

            return new string(chTemp.ToArray());
        }

        //交换数字
        protected void ChangeNum(ref string num1,ref string num2)
        {
            string strTemp = num1;
            num1 = num2;
            num2 = strTemp;
        }
        //获得较大数
        protected string Max(string num1, string num2)
        {
            if (num1.Length > num2.Length)
            {
                return num1;
            }
            else if (num1.Length==num2.Length)
            {
                for (int i = num1.Length-1; i >=0 ; i--)
                {
                    if (num1[i].CompareTo(num2[i])<0)
                    {
                        return num2;
                    }
                }
                return num1;
            }
            return num2;
        }
    }
--------------------------------------------------------------------------
    class BigAdd:BigCalculate
    {
        public override string Oper(string num1, string num2)
        {
            //获得较大数的位数
            int len = num1.Length > num2.Length ? num1.Length : num2.Length;
            //将较小数差位补0
            string tempNum1 = new string('0', len - num1.Length) + num1;
            string tempNum2 = new string('0', len - num2.Length) + num2;

            int flag = 0;//进位符
            List liCh = new List();//存放运算后数字
            for (int i = len - 1; i >= 0; i--)
            {
                liCh.Add((char)(tempNum1[i] + tempNum2[i] + flag - '0'));
                flag = (liCh[liCh.Count - 1] - '0') / 10;
                liCh[liCh.Count - 1] = (char)(((liCh[liCh.Count - 1] - '0') % 10) + '0');
            }

            //若运算完成后进位符不为0，及最高位进位，则再加一位
            if (flag > 0)
            {
                liCh.Add((char)(flag + '0'));
            }

            return InvertOrder(new string(liCh.ToArray()));
        }
    }