Using dtEnd.AddDays To Calculate Future Dates

I have an app that includes a calendar that allows users to select dates.   The customer wants to allow the users to schedule their meetings with this web page.  The user selects a date (like today) from a calendar.  Then, they enter a number in a field.  The code needs to calculate today's date plus the number of years entered in the text box and display that as a date.  Example:  today plus 5 years = 1/7/2019.

Here is the code that I'm trying to use to perform the calculation:

  {
        DateTime myStartDate, myEndDate;
        myEndDate.AddDays  (this displays the date selected by the calendar)

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Is there a tutorial or webpage that displays the proper formatting to do what I'm trying to do?  I've tried myEndDate.AddDays(1), myEnddate.addDays(-1), etc but nothing works.  As you can tell, I am new to this so any help is appreciated.