Question

I was wondering how one would go about changing the first digit (0-9) that comes after a capital letter (A-Z) in a string to an asterisk WITHOUT using sub. You can put this in a method called replace_digit if you want.

Answer 1

a = "not here 0 but here A5 and here B7, okay?"
begin
  loop do
    a[/(?<=[A-Z])\d/] = "*"
  end
rescue IndexError
end
puts a
# not here 0 but here A* and here B*, okay?

No sub 🙂

EDIT: I just noticed “first digit” – so just remove the loop; and if you can assume there will always be a match, you can remove the exception handling too.

a = "not here 0 but here A5 and here B7, okay?"
a[/(?<=[A-Z])\d/] = "*"
puts a
# not here 0 but here A* and here B7, okay?

EDIT2:

this works too, without lookbehind: a[/[A-Z](\d)/, 1] = "*"