C# 高精度加法 支持小数（待优化）

直接上代码

实现思路：

1、首先小数点补 位，9223372036854775808.9+9223372036854775808.9223372036854775808 => 9223372036854775808.900000000000000000+9223372036854775808.9223372036854775808

2、然后开始按位进行计算，进位数放入jw，在下一位计算时加上

   public static char[] Sum(string a, string b)

        {

            return Sum(a.ToCharArray(), b.ToCharArray());

        }

        public static char[] Sum(char[] a, char[] b)

        {

            char[] c = a;//补位后的a

            char[] d = b;//补位后的b

            int alength = a.Count();//a长度

            int blength = b.Count();//b长度

            int adot = alength;//a小数点位置

            int bdot = blength;//b小数点位置

            #region 小数点补位

            for (int i = 0; i < alength; i++)

            {

                if (a[i] == '.')

                {

                    adot = i;

                    break;

                }

            }

            for (int i = 0; i < blength; i++)

            {

                if (b[i] == '.')

                {

                    bdot = i;

                    break;

                }

            }

            if (adot != alength || bdot != blength)

            {

                if (adot == alength)

                {

                    c = new char[alength + 1 + blength - bdot - 1];

                    for (int i = 0; i < c.Length; i++)

                    {

                        if (i < alength)

                        {

                            c[i] = a[i];

                        }

                        else if (i == alength)

                        {

                            c[i] = '.';

                        }

                        else

                        {

                            c[i] = '0';

                        }

                    }



                }

                else if (bdot == blength)

                {

                    d = new char[blength + 1 + alength - adot - 1];

                    for (int i = 0; i < d.Length; i++)

                    {

                        if (i < blength)

                        {

                            d[i] = b[i];

                        }

                        else if (i == blength)

                        {

                            d[i] = '.';

                        }

                        else

                        {

                            d[i] = '0';

                        }

                    }

                }

                else

                {

                    if (alength - adot > blength - bdot)

                    {

                        d = new char[blength + ((alength - adot) - (blength - bdot))];

                        for (int i = 0; i < d.Length; i++)

                        {

                            if (i < blength)

                            {

                                d[i] = b[i];

                            }

                            else

                            {

                                d[i] = '0';

                            }

                        }

                    }

                    else

                    {

                        c = new char[alength + ((blength - bdot) - (alength - adot))];

                        for (int i = 0; i < c.Length; i++)

                        {

                            if (i < alength)

                            {

                                c[i] = a[i];

                            }

                            else

                            {

                                c[i] = '0';

                            }

                        }

                    }

                }

            }



            #endregion



            List<char> item = new List<char>();

            int cl = c.Length;

            int dl = d.Length;

            int r = 0;

            int jw = 0;//进位

            do

            {

                if (cl > 0 && dl > 0)

                {

                    if (c[cl - 1] == '.')

                    {

                        r = '.';

                    }

                    else

                    {

                        r = (int)c[cl - 1] + (int)d[dl - 1] - 96 + jw;

                        jw = 0;

                        if (r >= 10)

                        {

                            jw++;

                            r = r - 10;

                        }

                    }

                }

                else if (cl <= 0 && dl > 0)

                {

                    r = d[dl - 1] - 48+jw;

　　　　　　　　　　　 jw = 0;
                    if (r >= 10)
                    {
                        jw++;
                        r = r - 10;
                    }
                }

                else if (cl > 0 && dl <= 0)

                {

                    r = c[cl - 1] - 48+jw;
　　　　　　　　　　　 jw = 0;
                    if (r >= 10)
                    {
                        jw++;
                        r = r - 10;
                    }

                }



                if (r == 46)

                {

                    item.Add(Convert.ToChar(r));

                }

                else

                {

                    item.Add(Convert.ToChar(r.ToString()));

                }

                cl--; dl--;

            } while (cl > 0 || dl > 0);

            if (jw == 1)

            {

                item.Add('1');

            }

            return item.ToArray();

        }