inc13.obj : error LNK2019: unresolved external symbol "public: __thiscall CDistance::CDistance(void)" (??0CDistance@@QAE@XZ) referenced in function _main
In main() - Look at the definition of the object being created. Try adding some arguments to that (look at the signature of the constructor)
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CDistance(int, int);
// so use in main --->
CDistance d1(1,2);
Also if you want to overload the constructor, you must define both. You have only defined CDistance::CDistance(int f, int i) but declared and have not defined CDistance::CDistance();