What to do next after finishing a complete course??

Question

As I have finished my c++ course

Answer 1

Start practicing with what you learned to really engrave it into your mind. Also you can start another course. A related one will be good.
Like if you finished html start css they go hand in hand

Answer 2

Once you complete the course at the end you can see something "more on the topic" so try doing that to enhance your skills.