Algorithm to add or subtract days from a date?

Question

I\'m trying to write a Date class in an attempt to learn C++.

I\'m trying to find an algorithm to add or subtract days to a date, where Day starts from 1 and Month s

Answer 1

Don't know if this helps or not. I was working on a scheduling system which (in the first simple draft) calculated start date as due date - days lead time. I worked with seconds elapsed (since epoch) to allow greater precision in future drafts of the code.

#include 
#include 

int main() {
  // lead time in days
  int lead_time = 20;
  // assign a due_date of (midnight on) 3rd November 2020
  tm tm_due_date = { 0, 0, 0, 3, 11, 2020-1900};
  // convert due_date to seconds elapsed (since epoch)
  time_t tt_due_date = mktime(&tm_due_date);
  // subtract lead time seconds
  tt_due_date -= 60 * 60 * 24 * lead_time;
  // convert back (to local time)
  tm *start_date = localtime(&tt_due_date);
  // otput the result as something we can readily read
  std::cout << asctime(start_date) << "\n";
}