Need help with a code please help :D

[PierreA]

Are you using cmake or qmake? If cmake, you have a file CMakeLists.txt with a line like this:

add_executable(game main.cpp player.cpp game.cpp)

add_executable(game main.cpp player.cpp game.cpp)

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Add "spaceship.cpp" to the list of cpp files and your problem should go away.