DateTime.AddHours gives wrong output and datetime format changes

Question

I want DateTime in the following format.

DateTime a = Convert.ToDateTime(DateTime.UtcNow.ToString("s") + "Z");

Output:

2018-05-29T09:16:59Z

I want to subtract 4 hours from this time. So I have used this line of code:

var result = a.AddHours(-4);

Now, not only is the wrong time being shown, the above format is also disturbed.

29-05-2018 10:52:51

Expected Output:

2018-05-29T05:16:59Z

Answer 1

To get UTCNow minus 4 hours you'd want to do:

var fourHoursAgo = DateTime.UtcNow.AddHours(-4);
Console.WriteLine("fourHoursAgo: " + fourHoursAgo.ToString("yyyy-MM-ddTHH:mm:ssK"));

This will give an output like:

2018-05-29T05:36:18Z

This is basically an ISO 8601 format, very similar to DateTime.ToString("s"), but including the timezone ("Z" in this case.)