Pure-bred animals are available at much higher prices than strays. Often these dogs can be unhealthy and not worth the high price tag. People who see them in pet shop windows fall in love with them and only later realize that they have serious health problems. To find a healthy dog, do some research and deal directly with reputable dog breeders who are members of the American Kennel Club. Cats are fairly independent, though if you let your cat roam outside it could be injured or lost, and your neighbors might complain about it getting into fights.
Dogs cause more problems.
You could also be sued if your dog bites someone, or even another dog. Take these very sensible laws seriously. Dog and cat food can be found in most places that sell people food. Your local supermarket will have a special section for pet food and related pet products. It might even have a separate aisle or, in some immense supermarkets, a dog food aisle and a cat food aisle.