> For the complete documentation index, see [llms.txt](https://learncpp.benntan.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://learncpp.benntan.com/cpp-fundamentals/program-execution-model.md). # Program Execution Model When one develops a C++ program, it does not run directly. Instead, it goes through a fixed sequence of steps before your computer actually understands and executes it. ### Running Your Source Code Let's start with a simple single-file C++ program. The following *prints **Hello World*** to the console. {% code title="main.cpp" %} ```cpp #include int main() { std::cout << "Hello, world!"; return 0; } ``` {% endcode %} This file is called the **source code.** To run it, we need to compile the code: {% code title="" %} ```sh clang++ main.cpp -o hello-world ``` {% endcode %} This will produce an executable file called `hello-world` which your computer can finally run: {% code title="" %} ```sh ./hello-world ``` {% endcode %} Each time you make changes to the source code, you will need to compile again.

### What Just Happened ?! Think of a compiler as a black box that simply ***converts*** source code to machine code.

src: https://www.sitesbay.com/cpp/cpp-compiler

What does a compiler exactly do?

This is beyond the scope of this workshop. If you happen to be curious:

src: https://www3.ntu.edu.sg/home/ehchua/programming/cpp/gcc_make.html

Compiling a C++ source code is usually a 4 step process. It composes of **a) Preprocessing** where we substitute macros and header files with their actual content **b) Compilation** from C++ to platform-specific assembly **c) Assemble** where the resultant assembly code is assembled into actual object code **d) Linking** to link external library functions that the executable needs You can even pause the compilation process at each stage to inspect the immediate outputs using varying CLI flags.

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