Even back then this was considered poor practice, however. The first edition of K&R had a subsection entitled "Pointers are Not Integers" (I don't know if that's still in modern editions).
It looks to me like that section was removed in the 2nd edition. Some sections moved around, so maybe I'm just looking in the wrong place, but it's not nestled between "5.5 Character Pointers and Functions" and "5.7 Multi-Dimensional Arrays" like it is in the 1st edition.
The interesting thing for me is that a variable without a type annotation could potentially store anything. It kind of explains why the language used "int" as the default type of variables declared without a type annotation.