Datetime in C# add days

I want to add days in some date. I have a code like this:

DateTime endDate = Convert.ToDateTime(this.txtStartDate.Text); 
Int64 addedDays = Convert.ToInt64(txtDaysSupp.Text); 
endDate.AddDays(addedDays); 
DateTime end = endDate; 
this.txtEndDate.Text = end.ToShortDateString();

But this code is not working, days are not added! What the stupid mistake I'm doing?

DateTime is immutable. That means you cannot change it's state and have to assign the result of an operation to a variable.

endDate = endDate.AddDays(addedDays);

You need to catch the return value.

The DateTime.AddDays method returns an object who's value is the sum of the date and time of the instance and the added value.

endDate = endDate.AddDays(addedDays);

Its because the AddDays() method returns a new DateTime, that you are not assigning or using anywhere.

Example of use:

DateTime newDate = endDate.AddDays(2);

You can add days to a date like this:

// add days to current **DateTime**
var addedDateTime = DateTime.Now.AddDays(10);

// add days to current **Date**
var addedDate = DateTime.Now.Date.AddDays(10);

// add days to any DateTime variable
var addedDateTime = anyDate.AddDay(10);