How can I add a user interrupt to an infinite loop?

Question

I have a ruby script below which infinitely prints numbers from 1 onward. How can I make the script stop its infinite execution through an interrupt in the terminal like 'Ctrl+C' or key 'q'?

a = 0
while( a )
  puts a
  a += 1
  # the code should quit if an interrupt of a character is given
end

Through every iteration, no user input should be asked.