undefined reference error when trying to creat a simple class in c++

Question

im just started learning c++ from a youtube tutorial. i followed every step in the tutorial to creat a class but i always get the same error messege that says "undefined reference to Sally::Sally()".

i would appreciate your help, Thanks in advance.

this is the code :

main.cpp :

#include "Sally.h"
#include <iostream>
using namespace std;

int main()
{
    Sally sallyobject;

    sallyobject.printCrap();
}

Sally.h :

#ifndef SALLY_H
#define SALLY_H



class Sally
{
    public:
        Sally();
        void printCrap();
    protected:

    private:
};


#endif // SALLY_H

Sally.cpp

#include "Sally.h"
#include <iostream>
using namespace std;

Sally::Sally()
{
}


void Sally::printCrap(){

    cout << "printed me" << endl;

}