#!/usr/bin/ruby
# ranges_case_when_19.rb

puts "Student grading system"
print "Enter student mark: "
mark = gets.chop.to_i

grade = case mark
  when 80..100
    'A'
  when 60..79
    'B'
  when 40..59
    'C'
  when 0..39
    'D'
  else
    "Unable to determine grade. Try again."
end

puts "Your grade is #{grade}"