English Idioms (C)

Can't judge a book by its cover 

Cannot judge something primarily on appearance.

Caught between two stools

When someone finds it difficult to choose between two alternatives.

Costs an arm and a leg

This idiom is used when something is very expensive.

Cross that bridge when you come to it

Deal with a problem if and when it becomes necessary, not before.

Cry over spilt milk 

When you complain about a loss from the past.

Curiosity killed the cat 

Being Inquisitive can lead you into an unpleasant situation.

Cut corners

When something is done badly to save money.

Cut the mustard [possibly derived from "cut the muster"]

To succeed; to come up to expectations; adequate enough to compete or participate