Exercise from "Learning to Program" Chapter 7: Leap Year Generator. Insert two different years and the program will calculate all the leap year(s) between them.

gistfile1.rb

while true
  puts 'Start Year:'
  yearOne = gets.chomp.to_i
  puts 'End Year:'
  yearTwo = gets.chomp.to_i
  
  if yearOne > yearTwo
    startYear = yearTwo
    endYear   = yearOne
  else
    startYear = yearOne
    endYear   = yearTwo
  end
  if ((endYear - startYear) <= 4)
    puts ''
    puts 'ERROR!'
    puts '-----------------------------------------'
    puts 'Years need to be more than 4 years apart.'
    puts 'Please try again.'
    puts '-----------------------------------------'
    puts ''
  else
    puts ''
    puts 'Displaying leap years between ' + startYear.to_s + '-' + endYear.to_s + '.'
    while startYear <= endYear
      startYear = startYear + 1
      if startYear % 4 == 0 && ( startYear % 100 != 0 || startYear % 400 == 0 )
        puts startYear
      end
    end
    break
  end

end