字符串小数计算

输入两个小数a和b，用字符串表示，满足0

static string SDA(string a, string b)
        {
            int aLength = a.Length, bLength = b.Length;
            int minLength = Math.Min(aLength, bLength);
            bool isCarry = false;
            StringBuilder sb = new StringBuilder(minLength);
            for (int i = minLength - 1; i > -1; i--)
            {
                char tempA = a[i];
                if (!char.IsDigit(tempA))
                {
                    sb.Insert(0, tempA);
                    continue;
                }
                int tempDigit = (tempA - '0') + (b[i] - '0');
                if (isCarry)
                    ++tempDigit;
                if (tempDigit > 9)
                {
                    isCarry = true;
                    sb.Insert(0, tempDigit % 10);
                }
                else
                {
                    isCarry = false;
                    sb.Insert(0, tempDigit);
                }
            }
            return sb.ToString() + (minLength == aLength ? b[minLength..] : a[minLength..]);
        }

static string SDA2(string a, string b)
        {
            int aLength = a.Length, bLength = b.Length;
            int minLength = Math.Min(aLength, bLength);
            bool isCarry = false;
            Stack stacks = new Stack(minLength-1);
            for (int i = minLength - 1; i > -1; i--)
            {
                char tempA = a[i];
                if (!char.IsDigit(tempA))
                {
                    continue;
                }

                int tempDigit = (tempA - '0') + (b[i] - '0');
                if (isCarry)
                    ++tempDigit;
                if (tempDigit > 9)
                {
                    isCarry = true;
                    stacks.Push(tempDigit % 10);
                }
                else
                {
                    isCarry = false;
                    stacks.Push(tempDigit);
                }
            }
            StringBuilder sb = new StringBuilder(minLength);
            while (stacks.Count > 0)
            {
                sb.Append(stacks.Pop());
            }
            sb.Insert(1, ".");
            return sb.ToString() + (minLength == aLength ? b[minLength..] : a[minLength..]);
        }

static string SDA3(string a, string b)
        {
            int aLength = a.Length, bLength = b.Length;
            int minLength = Math.Min(aLength, bLength);
            bool isCarry = false;
            Stack