You’re writing in C/C++, using a library of functions with a fairly consistent API. There is no “Arduino language” and your “.ino” files are three lines away from being standard C++.

Unfortunately, the AD9833 doesn’t have a way to control amplitude, something which is pretty important in a function generator. So [Faransky] uses a X9C104P 100KOhm 8-bit digital potentiometer ...