In India, the common date format is
if (DateTime.TryParse(textBox1.Text, out d1))
string newDateTime = d1.ToString("yyyy/MM/dd hh:mmtt");
DateTime is a constructor that (in this case) attempts to create a specified date format from a string. In it's simplest structure, it is declared like this:
DateTime d1 = new DateTime (int, int, int);
You then have a
string which is a variable, with the name
newDateTime. This is simply a string, which holds a collection of characters.
You can format a string, as you have done in your example, which would rely on the data being passed in to have some form of structure. However, once the information has been passed in, it is just a string.