During an on-campus drive, we were first assessed through an online exam that primarily focused on pseudocode and pointers in C and C++. After passing this round, I was invited to a face-to-face interview that lasted about 45 minutes.

The interview began with a brief introduction, then quickly moved into questions about Visual Studio, breakpoints, and debugging techniques. The interviewer also asked about Object-Oriented Programming (OOP) concepts, including pure virtual classes and abstract classes, and requested that I write a code example for them. Additionally, I was asked to write a program to generate a Fibonacci series and then optimize it for better performance. Although I didn't receive the offer, it was a valuable learning experience.

Write a program to determine if a given number is a prime number.

Then, optimize your solution to improve its efficiency.