I want to clarify an important point here...you do NOT stop a cat from scratching! It's a natural behavior an they need to do it. You can make sure they scratch in designated areasm so they don't damage your carpet or furniture, but stopping a cat from scratching is akin to stopping a dog from sniffing.

We do nail trims here. Charlie in particular tends to get her claws snagged in the carpet if I don't keep hers trimmed. Nothing like a kitty halfway down the stairs crying because her foot is stuck to break your heart.