Отсутствуют экземпляры конструктора

#include <string>
using std::string;
 
class GradeBook
{
private:
    string Coursename;
    string Name;
public:
    GradeBook (string, string);
    void setcourse(string);
    void setname(string);
    string getcourse();
    string getname();
    void displaymessage();
};

#include <iostream>
using std::cout;
using std::endl;
#include "GradeBook.h"
//constructor
GradeBook::GradeBook (string coursename, string name)
{
    setcourse (coursename);
    setname (name);
}
//set function
void GradeBook::setcourse (string coursename)
{
    if (coursename.length()<=25)
        Coursename=coursename;
    if (coursename.length()>25)
    {
        Coursename=coursename.substr(0, 25);
        cout<<"Name of course "<<coursename<<" is too long. Max: 25 characters.\n"<<endl;
    }
}
void GradeBook::setname(string name)
{
    if (name.length()<=15)
        Name=name;
    if (name.length()>15)
    {
        cout<<"Limit is 15 characters.\n"<<endl;
        Name=name.substr(0, 15);
    }
}
string GradeBook::getcourse()
{
    return Coursename;
}
string GradeBook::getname()
{
    return Name;
}
void GradeBook::displaymessage()
{
    cout<<"Welcome to the grade book for "<<getcourse()<<"!"<<"\n";
    cout<<"By "<<getname()<<"."<<"\n";
}

#include <iostream>
using std::cout;
using std::endl;
#include "GradeBook.h"
int main()
{
    GradeBook course ("The C Programming");
    GradeBook name ("Denis Ritche");
 
    course.getcourse();
    name.getname();
}

GradeBook (string, string);

GradeBook::GradeBook (string coursename, string name)
{
    setcourse (coursename);
    setname (name);
}

int main()
{
    GradeBook course ("The C Programming"); // <--
    GradeBook name ("Denis Ritche");        // <--
 
    course.getcourse();
    name.getname();
}