How to calculate the number of days between two given dates? (Leap year obstacle)

Question

• Any year evenly divisible by 400 is a leap year (e.g., 2000 was a leap year).
• Any other year evenly divisible by 100 is not a leap year (e.g., 1700, 1800 and

Answer 1

Leap year algorithm from wikipedia:

Pseudocode 1:

if year modulo 400 is 0 then leap
 else if year modulo 100 is 0 then no_leap
 else if year modulo 4 is 0 then leap
 else no_leap

Pseudocode 2:

function isLeapYear (year):
  if ((year modulo 4 is 0) and (year modulo 100 is not 0)) or (year modulo 400 is 0)
   then true
  else false