Ошибка при использовании подключённых .h и .cpp компонентов

#include <iostream>
 
using namespace std;
 
#include "GradeBook.h"
 
int main()
{
   GradeBook gradeBook1("IS-13");
   GradeBook gradeBook2("IE-13");
 
   cout << "GradeBook 1: " << gradeBook1.getCourseName() << "\nGradeBook2:" << gradeBook2.getCourseName();
 
   return 0;
}

#include <string>
 
using namespace std;
 
class GradeBook
{
public:
   GradeBook( string );
   void setCourseName( string );
   string getCourseName();
   void displayMessage();
private:
   string courseName;
};

#include <iostream>
 
using namespace std;
 
#include "GradeBook.h"
 
 
 
GradeBook::GradeBook( string name )
{
   setCourseName( name );
}
 
void GradeBook::displayMessage()
{
   cout << "Welcome to\n" << getCourseName() << "\nGradeBook!" << endl;
}
 
void GradeBook::setCourseName( string name )
{
   courseName = name;
}
 
string GradeBook::getCourseName()
{
   return courseName;
}