Now, let me be completely straight and honest, if you need exercises in react, react won't be your career.
Do you know how reactive stuff are implemented in js? Do you know how those are implemented in C?
Can you implement them yourself in both js and C?
If you can do it, a component like a calculator is trivial and you just need to adjust the syntax and jargon. If you can't, this exercises will just be exercises in memorization and shallow understanding.
What I am saying is to learn how to implement the underneath engine in low level languages, it is much more fun and productive.
Anyhow, your life, your time! After all I am just a stranger on the internet.
