一个关于取字符串中数字和字符的逻辑问题

代码如下

 string a = "长花asdsad1236李代5415老花1213";

            int j = 0;
            int k = 0;
            bool id = true;
            
            for (int i = 0; i < a.Length;i++ )
            {
                if (a[i] >= '0' && a[i] <= '9')
                {
                    if (id)
                    {
                        k = i;
                        id = false;
                    }
                    if (i < a.Length - 1)
                    {
                        if (a[i + 1] >= '0' && a[i + 1] <= '9')
                        {
                            continue;
                        }
                        else
                        {
                            Response.Write(a.Substring(j, k - j) + ":" + a.Substring(k, i + 1 - k));
                            id = true;
                            j = i + 1;
                        }
                    }
                    else
                    {
                        Response.Write(a.Substring(j, k - j) + ":" + a.Substring(k, i + 1 - k));
                    }
                }
            }

输出结果为

长花asdsad:1236李代:5415老花:1213

这段代码还有待优化。希望大神指正