public string item(int i)
    {
        SqlConnection con = new SqlConnection(str_con);
        con.Open();
        string str_sql = "select item_text from item where item_id='"+i+"'";
        SqlCommand com = new SqlCommand(str_sql,con);
        SqlDataReader read = com.ExecuteReader(CommandBehavior.CloseConnection);
        read.Read();
       if (read.HasRows)
        {
            string str=((string)read["Item_text"]).Trim(); 字符串输出正常
            string[] str_array = str.Split('%');

            for (int k = 0;k < str_array.Length; k++) 错误提示k++无法访问的代码
            {
                string str_Split = str_array[k];
                return str_Split;
            }
        }
        con.Close();
        return null;
    }