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

I would convert the two dates in Julian day and then do the difference, but I would have to check if this is a good solution with no drawbacks first. I suggest you to do the same.