I have implemented the pure virtual method in the derived class but the compiler complains that I didn't

I have an abstract base class and its derived class, although I implemented the pure functions in the cpp file of the derived class, when I try to create an object of the derived I still get an error that says that the derived class is an abstract!! Base:

class Base  {
protected:
    string name;
    int quantity;
    double price;
public:
    c'tor....
    virtual ~Base(){}
    virtual void buy(int num) = 0;
    };

Derived:

#include "Base.h"

class Derived : public Base{
protected:
    double percentage;
public:
    c'tor...
    virtual ~Derived() {}
    virtual void buy(int num);

};

Derived.cpp:

#include "Derived.h"
void Derived::buy(int num){
   //implementation
}

main.cpp:

#include "Base.h"
#include "Derived.h"
int main()   {
    Derived d;
    //...
}

Error:

1   IntelliSense: object of abstract class type "Derived" is not allowed:
            pure virtual function "Base::buy" has no overrider  c:UsersaubDocumentsVisual Studio 2013ProjectsProject22Project22main.cpp 10