Question

I'm looking at homework 1, optional exercise 1 (Zeller's algorithm). The instructions have a contradiction when the month is Jan or Feb. At one point it says to subtract 1 from C, then it says to use the preceding year. They are not the same--it makes a difference when the year ends in 0, as in the year 2000. If you use the preceding year, year = 2000-1 = 1999; C = 99. But if you subtract 1 from C, year = 2000; C = 0-1 = -1. Any idea which is meant?

Answer 1

I think I figured this out by looking online. Other explanations of Zeller's algorithm clarified that you actually do use the preceding year--so subtract 1 from the year, then calculate C.

One reason I was asking is because I kept getting incorrect output for the years 1000 and 1100 and thought it might have to do with how I was calculating C. I found this explanation online:

"This uses the Gregorian calendar, which is our current standard. There are other calendars in use in the world. As the Gregorian calendar was devised in 1582, fixing the cumulative errors of the preceding Julian calendar, it is not clear that Zeller's algorithm will work properly for dates before 1582."