DateTime Object does not implement public functions

[tosandeepgarg]

DateTime object does not have most of the public methods available. For example all Add methods like Add,AddDays, AddMonths, AddYears etc.
Here is test case.

using System;

public static class Program
{
    public static void Main(string[] args)
    {
        var s = DateTime.Now;
        Console.WriteLine(s.AddDays(1));
    }
}