Unable to login due to broken key on built-in keyboard The 0 (zero) key on my MacBook's built in keyboard stopped working. I am unable to login as the password contain that character.

Do I need to get an external USB keyboard to login? Is there an on screen keyboard that can be invoked without logging in? I have a 201 MacBook Air.
An external USB keyboard will allow you to log on. Then you can change your password using the external keyboard, and you will be able to log on with the internal keyboard again. But you won't be able to type the character 0 ever again, unless you get the keyboard fixed.