Question

Does anyone know a way to convert a month, year, and day into the day’s name for any year? Example:

function convert(day, year, month)
...
return "Monday"
end

Thanks in advance!

Answer 1

You can use the following method:

This method uses codes for different
months and years to speed up the
calculation of the day of the week.
You might even be able to memorize the
codes. We’ll use December 16, 2482 as
an example.

Take the last 2 digits of the year. In
our example, this is 82.

Divide by 4, and drop any remainder.
82 / 4 = 20, remainder 2, so we think
“20.”

Add the day of the month. In our
example, 20 + 16 = 36.

Add the month’s key value, from the
following table. Jan Feb Mar Apr May
June July Aug Sept Oct Nov Dec 1 4 4
0 2 5 0 3 6 1 4 6

The month for our example is December,
with a key value of 6. 36 + 6 = 42.

If your date is in January or February
of a leap year, subtract 1. We’re
using December, so we don’t have to
worry about this step.

Add the century code from the
following table. (These codes are for
the Gregorian calendar. The rule’s
slightly simpler for Julian dates.)
1700s 1800s 1900s 2000s 4 2 0 6

Our example year is 2482, and the
2400s aren’t in the table. Luckily,
the Gregorian calendar repeats every
four hundred years. All we have to do
is add or subtract 400 until we have a
date that is in the table. 2482 – 400
= 2082, so we look at the table for the 2000s, and get the code 6. Now we
add this to our running total: 42 + 6
= 48.

Add the last two digits of the year.
48 + 82 = 130.

Divide by 7 and take the remainder.
This time, 1 means Sunday, 2 means
Monday, and so on. A remainder of 0
means Saturday.

How to calculate the day of the week