Implementing a date algorithm

In this section, we are going to see how to solve another fun and challenging math problem where we will build an efficient solution to this question: how many Sundays fell on the first of the month during the twentieth century (January 1, 1901, to December 31, 2000)?

To solve this problem, first we have to add the date library to our code file. From there, we can set up some variables:

require 'date'

start_date = Time.local(1901)
end_date = Time.local(2000,12,31)
sunday_counter = 0 

The first variable start_date has the starting date of the problem. By default, the local method starts with January 1 so there is no need to specify the actual day. However, we need to specify the exact date for our end_date variable. The third variable sunday_counter will count the number of Sundays that fell on the first of the month during the period between start_date and end_date.

Next, we are going to create a while loop:

while end_date >= start_date
  if end_date.strftime...