I want to create Task in Google Calendar using Google Calendar API.Using C#. Looking for some sample codes.
Unfortunately, there is no API for the Tasks feature in Google Calendar. While the Calendar Data API is pretty extensive, the Tasks team hasn't released an API yet. Many people, including you, have requested such an API, but Google hasn't done anything to fill the gap yet. There are many posts on the Data API group about this, such as this one.
However, Google might release one into the wild soon. Until then, if you really need to use Tasks, you're going to have to do screen-scraping. In other words, you have to investigate how the GCalendar UI works and mimic interaction with it.
Some people have probably approached this problem and created screen-scraping libraries. After searching a little bit, I haven't found a C# one. If you do decide to take this approach, please create an open-source library for the benefit of others who want to accomplish such a task.
Good luck!