Day of the week: Difference between revisions

=={{header|Forth}}==

Forth has only TIME&DATE, which does not give day of week. Many public Forth Julian date calculators had year-2100 problems, but this algorithm works well.

\ Zeller's Congruence

: zeller ( m -- days since March 1 )

9 + 12 mod 1- 26 10 */ 3 + ;

: weekday ( d m y -- 0..6 ) \ Monday..Sunday

over 3 < if 1- then

dup >r

r@ 4 / +

r@ 100 / -

r> 400 / +

swap zeller + +

1+ 7 mod ;

: yuletide

." December 25 is Sunday in "

2122 2008 do

25 12 i weekday

6 = if i . then

loop cr ;