How to compile C++ code with separate interface? (Arq.h , Arq.cpp and main.cpp)

Question

I’m studying C++ for the Deitel book and I’m trying to compile a program where we have a gradebook file. h which is the interface, gradebook.cpp which is the implementation and main.cpp. Whenever I run the program it returns me indefinite reference errors. I already executed a tip from a colleague here in another post (g++ -o gradebook gradebook.cpp main.cpp), in this case does not return me the errors, however, also does not return me anything in the terminal. simply compile and finish. Follow the code:

main.cpp

#include <iostream>
#include "gradebook.h" // definição de classe GradeBook
using namespace std;

int main()
{
    //cria dois objetos GradeBook
    GradeBook gradeBook1( "CS101 Introduction to Programming in C++" );
    GradeBook gradeBook2( "CS102 Data Structures in C++ ");

    //exibe courseName de cada GradeBook
    cout << "gradeBook1's initial course name is: " << gradeBook1.getCourseName()
         << "\ngradeBook2's initial course name is: " << gradeBook2.getCourseName() << endl;

    //modifica courseName do myGradeBook (com uma string de comprimento valido)
    gradeBook1.setCourseName( "CS101 C++ Programming");

    //Exibe valor inicial de courseName para cada GradeBook
    cout << "\ngradeBook1's course name is: " << gradeBook1.getCourseName() 
         << "\ngradeBook2's course name is: " << gradeBook2.getCourseName()
         << endl;
    return 0;
}

gradebook.cpp

#include <iostream>
#include "gradebook.h" //Definição de classe GradeBook
using namespace std;

GradeBook::GradeBook( string name )
{
    setCourseName( name );
}

void GradeBook::setCourseName( string name )
{
    if ( name.length() <= 25 )
    {
        courseName = name;
    }
    
    if ( name.length() > 25 )
    {
        courseName = name.substr( 0, 25 );

        cout << "Name \"" << name << "\" exceeds maximum lenght (25). \n"
             << "Limiting courseName to first 25 characters.\n" << endl;
    }
}

string GradeBook::getCourseName()
{
    return courseName;
}

void GradeBook::displayMessage()
{
    cout << "Welcome to the grade book for\n" << getCourseName() << "!" << endl;
}

gradebook. h

#include <string> // a classe GradeBook utiliza a classe de string padrao C++
using namespace std;

class GradeBook
{
    public:
        GradeBook( string ); // Construtor que inicializa courseName
        void setCourseName( string ); //configura o nome do curso
        string getCourseName(); // obtem o nome do curso
        void displayMessage(); // exibe mensagem de boas vindas
    private:
        string courseName; //nome do curso para este GradeBook
};