Omission of Articles

The indefinite article is omitted in the following cases: after être and devenir with names of occupations, religions, creeds, etc.

Son frère est musicien.
(His brother is a musician.)

Il espère devenir catholique.
(He hopes to become a Catholic.)

However, the article is used when the noun is introduced by c'est:

C'est un docteur très connu.
(He is a well-known doctor.)

after the exclamatory adjectives quel, quelle, quels, quelles:

Quelle vie!
(What a life!)

Quel gros problème!
(What a big problem!)

after comme (as):

Je travaille comme assistant.
(I work as an assistant.)

before the numbers cent et mille:

Je vois mille étoiles dans le ciel; cent brillent.
(I see a thousand stars in the sky and one hundred are shining.)

after ni in the expression ni...ni (neither...nor):

Je n'ai ni voiture ni bicyclette.
(I have neither car nor bicycle.)

in numerical titles of monarchs:

Louis quatorze (Louis XIV)
(Louis the Fourteenth)