All dinosaurs are reptiles, including birds. The major clade of dinosaurs to which birds belong is called theropods. The other well-known dinosaurs, sauropods (including all the huge quadrupedal herbivores), are totally extinct and have only very distant ancestry with birds and other reptiles.

By the way, crocodilians have been around for 250 million years, so they shared the earth with the huge dinosaurs of old! But they are not dinosaurs themselves.