This repo is first part of object-implementation programming in C language. Perhaps you will be wondering why not use C++ instead, why "reinvent the wheel", because the repo's purpose is just simply to learn some advanced skills in C such as struct, function pointer, static function,...

1. Abstraction: provide public attributes and methods such as: username and getPassword(). ✅
2. Encapsulation: hiding private attributes and methods such as: password, encodePassword(), decodePassword(). ✅
3. Inheritance: maybe use structs and preprocessor directives.
4. Polymorphism: maybe use function pointers and preprocessor directives [].
5. Interface: maybe use header declarations and preprocessor directives [].