program of class with rescue,raise in ruby program

#class with rescue and raise in ruby program

class Question
attr_accessor  :a1, :a2
def initialize(a1,a2)
@a1=rand(50)
@a2=rand(50)

end
def make_random_substraction
begin
puts 'Random Substraction of two numbers.'

puts "What is '#@a1' - '#@a2' ?"


@a3 = Integer(@a1) - Integer(@a2)
puts "#@a3"

if @a3<0
raise 'exception'
end

rescue
puts "An exception : answer is in negative value."
puts "Lets retry it in other order."
@a3 = Integer(@a2) - Integer(@a1)

puts "Here, answer is : #@a3"
 
end
end
end
obj=Question.new(@a1,@a2)
obj.make_random_substraction

OUTPUT:

Random Substraction of two numbers.

What is '18' - '1' ?

17