== vs ===
Loose vs strict comparison and PHP type juggling.
implode() vs explode()
Converting between arrays and strings, both directions.
include vs require
What happens when a file is missing, and the _once variants.
array_combine() vs array_merge()
Zipping keys to values vs stacking arrays together.
sort vs asort vs ksort
Sorting by value, keeping keys, or sorting by key.
Fibonacci series
Turn the rule into a loop — plus the recursion follow-up.
Find & remove a value
in_array, array_search, and removing an element cleanly.
OOP: Classes & Objects
The first step into object-oriented PHP — blueprint vs instance.
OOP: Constructors
Use __construct to set up an object the moment it is created.
OOP: Encapsulation
public/private/protected + getters and setters — protect your data.
OOP: Inheritance
extends, parent:: and overriding — reuse a parent class.
OOP: Abstraction
abstract classes and methods — a template children must complete.
OOP: Interfaces
interfaces as pure contracts, plus abstract class vs interface.
OOP: Polymorphism
one method call, many forms — the fourth pillar of OOP.