When a cat holds it s tail up, it means it is happy, but in dogs, how high they hold their tail is how they determine ranks. If one dog meets another dog, and one holds it tail up, it is the one of the higher social class. Another difference is that cats are nocturnal, meaning they go out at night. Dogs, however, are day animals. Another very obvious difference between dogs and cats is that dogs are usually bigger than cats.
Cats are usually scared of dogs, and the dogs usually chase the cats.
Dogs are also somewhat smarter than cats in the area of verbal command. For example, you can call your dog by name and usually it will come to you, unlike a cat. Also, you can train dogs to do tricks when commanded. Some of the most commonly seen tricks in dogs are role over, fetch, shake hands, sit down, lay down, and play dead. I have never seen a cat do any of these things, and I doubt that I ever will get an opportunity to see a cat preform even one of these tricks.