On Day 4, we shift to building real-world systems using Object-Oriented Programming. You’ll learn about classes, objects, constructors, methods, and abstraction techniques like _private and __hidden. We’ll cover clean OOP practices, basic file I/O, and build simple projects like a Student Grade Manager or ATM Simulator. We’ll also discuss when to use AI tools like Cursor and ChatGPT responsibly. The day ends by reinforcing why clean, modular code matters—and setting you up for independent learning.