C# tostring("0000000")

 public string ConverNo(string str)
        {
            string result = "";

            char[] chars = new char[];
            for (int i = ; i < chars.Length; i++)
            chars[i] = '';
            char[] chars1 = str.ToArray(); //字符串生成数组

            string str0 = "";
            result =  str0.Substring(,str0.Length-str.Length);
            result = result += str;

            return "";
        }