Regular Expression to match a valid day in a date

Question

I need help coming up with a regex to make sure the user enters a valid date The string will be in the format of mm/dd/yyyy

Here is what I have come up

Answer 1

Regex for 0-31 day:

0[1-9]|[12]\d|3[01]) without prefix 0 - when "1", "23"...

([1-9]|[12]\d|3[01]) with prefix 0 - when "01", "04"

(0?[1-9]|[12]\d|3[01]) - with or without "0" - when ""