cien ADJECTIVE, PRONOUN a hundred
Cien is the shortened version of ciento and both mean a hundred. Which one you need to use depends on the words that come before or after.
You use cien in front of a noun, as in the title of the famous novel by García Márquez, Cien años de soledad A Hundred Years of Solitude and as in the following examples:
Esta película es cien veces mejor que la anterior. This film is a hundred times better than the last one.
a unos cien metros de aquí about a hundred metres from here
or in front of mil a thousand and millones millions:
cien mil personas a hundred thousand people
cien millones de dólares a hundred million dollars
In front of other numbers, you use ciento.
ciento once a hundred and eleven
en la página ciento treinta on page one hundred and thirty
Remember that there is no y between ciento and the numbers following it.