Header files and several sources

Declarations in a .hpp / .h file, definitions in a .cpp file; the IDE links them into your program.

Runs in Zerethon IDE · C++ (GCC 14) Official C++ documentation ↗

main.cpp

#include <iostream>
#include "geometry.hpp"

int main() {
    std::cout << geometry::area(3, 4) << '\n';
}

geometry.hpp

#pragma once

namespace geometry {
int area(int width, int height);
}

geometry.cpp

#include "geometry.hpp"

namespace geometry {
int area(int width, int height) { return width * height; }
}

Output

Run compiles the entry together with every other .cpp / .cc file whose name does not start with main or test_.
#pragma once (or an include guard) stops a header from being included twice.
Only the C++ standard library is available; other libraries (Boost, fmt, …) are not installed.

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