Easy way to determine leap year in ruby?

For your understanding:

def leap_year?(year)
  if year % 4 == 0
    if year % 100 == 0
      if yearVar % 400 == 0
        return true
      end
      return false
    end
    return true
  end
  false
end

This could be written as:

def leap_year?(year)
  (year % 4 == 0) && !(year % 100 == 0) || (year % 400 == 0)
end

Use Date#leap?.

now = DateTime.now 
flag = Date.leap?( now.year ) 

e.g.

Date.leap?( 2018 ) # => false

Date.leap?( 2016 ) # => true

Try this:

is_leap_year = year % 4 == 0 && year % 100 != 0 || year % 400 == 0

Here is my answer for the exercism.io problem which asks the same question. You are explicitly told to ignore any standard library functions that may implement it as part of the exercise.

class Year
  attr_reader :year

  def initialize(year)
    @year = year
  end

  def leap?
    if @year.modulo(4).zero?
      return true unless @year.modulo(100).zero? and not @year.modulo(400).zero?
    end

    false
  end
end