How could I use the length of an array in a c++ function?

Question

I can't seem to be able to use the length of an array in a c++ function. Sizeof seems to return the wrong number(for an array of 5, it's returning 8) and .size() just gave me an error.

Edit: Here's an example

https://code.sololearn.com/cNsk28yY7n1d/?ref=app

Answer 1

https://code.sololearn.com/c3nZK46tiN3Z/?ref=app