static void Main(string[] args)
        {
            string json = File.ReadAllText("sample.txt");
            JArray a = JArray.Parse(json);
            List<Example> list = new List<Example>();
            foreach (JObject content in a.Children<JObject>())
            {
                list.Add(new Example() { uid = content["uid"].ToString(), email = content["email"].ToString(), completed_percentage = Convert.ToDouble(content["php.completed_percentage"]) });
            }
            WriteCSV(list, "test.csv");
        }

        public static void WriteCSV<T>(IEnumerable<T> items, string path)
        {
            Type itemType = typeof(T);
            var props = itemType.GetProperties(BindingFlags.Public | BindingFlags.Instance)
                                .OrderBy(p => p.Name);

            using (var writer = new StreamWriter(path))
            {
                writer.WriteLine(string.Join(", ", props.Select(p => p.Name)));

                foreach (var item in items)
                {
                    writer.WriteLine(string.Join(", ", props.Select(p => p.GetValue(item, null))));
                }
            }
        }

  public class Example
    {
        public string uid { get; set; }

        public string email { get; set; }

        public double completed_percentage { get; set; }
    }