Look carefully at Shape.h$.$ Note how it declares protected fields volume and surfaceArea $($so all shapes have them$),$ and it requires getVolume, getSurfaceArea, compareVolume, and compareSurfaceArea to be written in Shape.cpp$.$ But the other functions are virtual and $=0.$ These cannot be written in Shape.cpp$,$ and instead MUST be written in the subclasses.

Cylinder$/$Cube$/$Sphere$.$cpp: In their header files, notice that in addition to the simple constructors and getters$/$setters$,$ all of the pure virtual functions are listed here, still with the keyword virtual, but without the $=0.$ All of these must be implemented per usual.