It’s not in C, if that’s what you mean.

It’s a “stream manipulator” function that not only generates a new line, it also flushes the stream.

Probably moreso for expressing the opinion so strongly without actually knowing any of the three languages.

Edit: I’m just guessing why a different comment got downvotes. Why am I getting downvotes?

Doesn’t the first edition use K&R style parameter lists and other no-longer-correct syntax?