Learn Italian: Il contadino ha cento pecore. - The farmer has one hundred sheep.

In Italian, the numbers cento (a hundred / one hundred) and mille (a thousand / one thousand) do not take an indefinite article like un before them. You simply say cento pecore.

Does cento ever change its ending to match the plural noun?

No, cento is invariable, meaning it never changes form. Whether it is attached to a masculine or feminine noun, or combined to make larger numbers like cinquecento (five hundred), it always stays cento.

In English, "sheep" is both singular and plural. How does this work in Italian?

Italian treats it as a regular feminine noun. A single sheep is una pecora, and multiple sheep are le pecore. Since the farmer has a hundred of them, we use the plural form pecore.

Are there other words for "farmer" besides contadino?

Yes, contadino is the most common, everyday word for a traditional farmer or peasant (it comes from contado, meaning countryside). You might also see agricoltore, which is a slightly more formal word for an agricultural worker.