Sort a vector of different class objects in c++?

Question

I have a vector of different class objects. And I want to sort the vector using the the top level variable percentage in the Grading class. I override the method for operator< for all the classes but for some reason it keeps on sorting using by the name variable.

Here is the design of the classes.

Here is the code

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <iterator>
#include <iomanip>
using namespace std;


/* -------------------------------------------------------- */
/* ---------------------- Grading Class ------------------- */
/* -------------------------------------------------------- */
class Grading
{
public:
    string name;
    int percent;

    void get_raw_score();
    void get_adj_score();

    virtual void print() { }

};

bool operator< (const Grading& a, const Grading& b) const {
    return (a.percent < b.percent);
}

/* -------------------------------------------------------- */
/* ---------------------- Assignment Class ---------------- */
/* -------------------------------------------------------- */
class Assignment : public Grading
{
public:
    int score;

    void print() {
        cout << name << std::setw(20) << percent << std::setw(20) << score << endl;
    }

};

bool operator< (Assignment& a, Assignment& b) {
        return (a.percent < b.percent);
    }

/* -------------------------------------------------------- */
/* ---------------------- Exam Class ---------------------- */
/* -------------------------------------------------------- */
class Exam : public Grading
{
public:
    int score;

    Exam(string n, int g, int s) {
        name = n;
        percent = g;
        score = s;
    }

    void print() {
        cout << name << std::setw(20) << percent << std::setw(20) << score << endl;
    }

};

bool operator< (Exam& a, Exam& b) {
    return (a.percent < b.percent);
}

/* -------------------------------------------------------- */
/* ------------------- Project Class ---------------------- */
/* -------------------------------------------------------- */
class Project : public Assignment
{
public:

    string letter_grade;

    Project(string n, int g, string l_g) {
        name = n;
        percent = g;
        letter_grade = l_g;
    }

    void print() {
        cout << name << std::setw(20) << percent << std::setw(20) << letter_grade << endl;
    }

};

bool operator< (Project& a, Project& b) {
    return (a.percent < b.percent);
}


/* -------------------------------------------------------- */
/* ---------------------- Quiz Class ---------------------- */
/* -------------------------------------------------------- */

class Quiz : public Exam
{
public:

    string letter_grade;

    Quiz(string n, int g, string l_g) : Exam(n, g, score)
    {
        name = n;
        percent = g;
        letter_grade = l_g;
    }

    void print() {
        cout << name << std::setw(20) << percent << std::setw(20) << letter_grade << endl;
    }

};

bool operator< (Quiz& a, Quiz& b) {
    return (a.percent < b.percent);
}


/* -------------------------------------------------------- */
/* ---------------------- CourseWork class ---------------- */
/* -------------------------------------------------------- */

class CourseWork {

public:
    CourseWork() {}

    void push_back(Grading* a) {
        work.push_back(a);
    }

    // print the data and sort by name
    void sort_name() {
        std::sort(work.begin(), work.end(), greater<Grading *>());
    }

    void sort_score() {
        std::sort(work.begin(), work.end(), less<Grading *>());
    }

    friend ostream& operator<<(ostream& os, const CourseWork& dt) {

        cout << "Grading" << std::setw(20) << "Percentage" << std::setw(20) << "Raw-Score" << endl;
        for (int i = 0; i < (int)dt.work.size(); i++) {
            dt.work.at(i)->print();
        }

        return os;
    }


private:
    vector<Grading*> work;
};

/* -------------------------------------------------------- */
/* ---------------------- MAIN ---------------------------- */
/* -------------------------------------------------------- */

int main () {
    CourseWork c;

    c.push_back(new Quiz("Quiz", 5, "B-"));
    c.push_back(new Quiz("Quiz", 5, "C+"));
    c.push_back(new Quiz("Quiz", 5, "A"));
    c.push_back(new Exam("Midterm", 10, 50));
    c.push_back(new Exam("Final", 30, 85.5));
    c.push_back(new Project("Project", 5, "A-"));
    c.push_back(new Project("Project", 15, "B-"));
    c.push_back(new Project("Project", 15, "B-"));
    c.push_back(new Project("Demo", 10, "C"));

    cout << "** Showing populated data..." << endl;
    cout << c << endl << endl;; 

    c.sort_name();
    cout << "** Showing sorted by name..." << endl;
    cout << c << endl << endl;

    c.sort_score();
    cout << "** Showing sorted by score..." << endl;
    cout << c << endl; 

    // c.sort_score();

    return 0;
}

SOLVED

bool GradingCompare (Grading* l, Grading* r) {
    return (l->percent < r->percent);
}

void sort_name() {
    std::sort(work.begin(), work.end(), greater<Grading *>());
}