What is the use of internal, protected, and protected internal?

Short answer: Internal → Accessible only within the same assembly. Protected → Accessible in the class and derived classes. Protected Internal → Accessible in derived classes or within the same assembly.

Example code

protected string accountType; // accessible in derived classes internal string branchCode; // accessible within same assembly

Real-world example (ShopNest)

Think of ShopNest’s Product, Cart, and Order classes: each object holds data + behavior, so pricing rules stay next to the data they use.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.