Day of week calculator off by 1 day

Mar 18, 2016 at 10:54pm
One of my class assignments is to create a program that calculates the day of the week by first calculating the Julian day number, adding one and doing a % 7 operation. I am told that days are numbered from 0 to 6, 0 being Sunday. When I enter today's date, I get "Thursday" - and today's Friday. My program appears to have calculated the Julian day number correctly.
Here's the line I think is causing the problem.
 
 int dayNum = ((long)JDN + 1) % 7;
Last edited on Mar 18, 2016 at 11:51pm
Mar 19, 2016 at 3:46am
I have no knowledge about julian day conversion, but does it have anything to do with this year being a leap year? Did you try a day prior to Feb. 29? I could be wrong, but that's the first thing that comes to my mind for this year.
Mar 19, 2016 at 12:37pm
What day of the week was Julian day zero? The answer to that question determines what you have to add to JDN before doing the modulus.

Another possible bug: how are you printing out the day of the week? Maybe you're setting dayNum correctly but printing the wrong string.
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