CPP
What is CPP
C++ is the primary programming language used throughout the 
Source engine and its toolchain. It is a compiled, statically-typed language that offers high performance and fine-grained control over memory and system resources making it ideal for game engine development.
C++ supports multiple programming paradigms, including procedural, object-oriented, and generic programming. It introduces features such as classes, inheritance, virtual functions, and templates, all of which 
Valve used extensively in Source to build complex, modular systems.
Most engine code, game logic, tools, and extensions in Source are written in C++. Familiarity with the language is essential for working with the 
Source SDK, modifying game .dlls, or creating new engine features.
Where to Learn CPP
The Source SDK is not the best when it comes to learning C++. So here are alternatives to help get you started: