You might be telling the compiler you want the file "GameEngine.h", but you probably aren't telling it where to look for it. You have to add the directory that "GameEngine.h" is in to your compiler's search/include path. It's a simple process, though I don't know what IDE you're using (assuming you're using one), so I can't give you specific instructions. This can usually be done by going into the project's options and then specifying additional include directories you want the compiler to look in.