title: Algorithm to add or subtract days from a date?
body: <p>I'm trying to write a Date class in an attempt to learn C++.</p>
  
  <p>I'm trying to find an algorithm to add or subtract days to a date, where Day starts from 1 and Month starts from 1. It's proving to be very complex, and google doesn't turn up much,</p>
  
  <p>Does anyone know of an algorithm which does this?</p>