i want to have a dog

Depends where you live and a bunch of other things people already listed here, going with a cat might be a lot less trouble then a dog but that's just what i think after owning like 6 dogs and over 23 cats (i had a few cats that had a lot of kittens) over the course of my life.

Best of luck if you get a dog, its a lot to take care of if you live in a city.