Count number of Mondays in a given date range

Question

Given a date range, I need to know how many Mondays (or Tuesdays, Wednesdays, etc) are in that range.

I am currently working in C#.

Answer 1

Convert the dates to Julian Day Number, then do a little bit of math. Since Mondays are zero mod 7, you could do the calculation like this:

JD1=JulianDayOf(the_first_date)
JD2=JulianDayOf(the_second_date)
Round JD1 up to nearest multiple of 7
Round JD2 up to nearest multiple of 7
d = JD2-JD1
nMondays = (JD2-JD1+7)/7    # integer divide