Не существует подходящей функции преобразования из "const std::string" в "double"

#include <iostream>
#include <string>
#include <fstream>
#include <algorithm>
using namespace std;
 
class Contingent {
protected:
    string firstname, lastname;
    int age;
public:
    Contingent(string = "John", string = "Jones", int = 32);
    ~Contingent() = default;
    void printClass()const;
};
class HeightSchool {
protected:
    string name;
    int departments;
public:
    HeightSchool(string = "Brighton", int = 5);
    ~HeightSchool() = default;
    void printClass()const;
    double getPub()const;
};
class Bachelor :public Contingent, public HeightSchool {
    string specialty;
    int grade;
public:
    Bachelor(string = "Chemist", int = 51);
    ~Bachelor() = default;
    bool operator <(const Bachelor&);
    friend istream& operator >>(istream&, Bachelor&);
    friend ostream& operator <<(ostream&, const Bachelor&);
};
Contingent::Contingent(string f, string l, int a) :
    firstname(f), lastname(l), age(a) {}
 
void Contingent::printClass()const {
    cout << "Saxeli: " << firstname
        << "\nGvari: " << lastname
        << "\nAsaki: " << age << endl;
}
 
HeightSchool::HeightSchool(string n, int d) :
    name(n), departments(d) {}
 
void HeightSchool::printClass()const {
    cout << "Dasaxeleba: " << name
        << "\nFakultetebis ricxvi: " << departments << endl;
}
double HeightSchool::getPub()const { return name; }
 
Bachelor::Bachelor(string s, int g) :
    Contingent(), HeightSchool(), specialty(s), grade(g) {}
 
bool Bachelor::operator <(const Bachelor& l) {
    return this->grade < l.grade;
}
 
istream& operator >>(istream& in, Bachelor& l) {
    return in >> l.firstname >> l.lastname
        >> l.age >> l.name >> l.departments
        >> l.specialty >> l.grade;
}
 
ostream& operator <<(ostream& out, const Bachelor& l) {
    return out << "Saxeli: " << l.firstname
        << "\nGvari: " << l.lastname
        << "\nAsaki: " << l.age
        << "\nDasaxeleba: " << l.name
        << "\nFakultetebis ricxvi: " << l.departments
        << "\nSpecialoba: " << l.specialty
        << "\nShefaseba: " << l.grade << endl;
}
 
void fillArray(Bachelor*, int&);
void printArray(const Bachelor*, int&);
void intoFile(const Bachelor*, int&);
 
int main() {
    static Contingent C("Dustin", "Poirier", 32);
    C.printClass();
    cout << "--------------------" << endl;
 
    static HeightSchool H("Tonbridge", 4);
    H.printClass();
    cout << "--------------------" << endl;
 
    Bachelor* ptr = new(nothrow) Bachelor[1200];
    int realSize{ 0 };
    fillArray(ptr, realSize);
    sort(ptr, ptr + realSize, [](Bachelor& k, Bachelor& l) { return l < k; });
    printArray(ptr, realSize);
 
    intoFile(ptr, realSize);
 
    delete[] ptr;
    ptr = nullptr;
}
 
void fillArray(Bachelor* arr, int& n) {
    ifstream ifs("bachelor.txt");
    while (!ifs.eof()) {
        ifs >> arr[n++];
    }
    ifs.close();
}
 
void printArray(const Bachelor* arr, int& n) {
    for (int i = 0; i < n; ++i) {
        cout << arr[i];
        cout << "--------------------" << endl;
    }
}
 
void intoFile(const Bachelor* arr, int& n) {
    ofstream ofs("report.txt");
    ofs << "Yvelaze udidesi shefaseba:\n\n";
    for (int i = 0; i < n; ++i) {
        ofs << arr[i];
        if ((arr + i)->getPub() != (arr + i + 1)->getPub()) {
            break;
        }
    }
    ofs << "--------------------" << endl;
 
    ofs << "Yvelaze umciresi shefaseba:\n\n";
    for (int i = n - 1; i >= 0; ++i) {
        ofs << arr[i];
        if ((arr + n - i)->getPub() != (arr + n - i - 1)->getPub()) {
            break;
        }
    }
    ofs << "--------------------" << endl;
 
    int average = 0;
    for (int i = 0; i < n; ++i) {
        average += (arr + i)->getPub();
    }
    average /= n;
 
    int index = 0, dif = abs((arr)->getPub() - average);
    for (int i = 1; i < n; ++i) {
        if (abs((arr + i)->getPub() - average) < dif) {
            index = i;
            dif = abs((arr + i)->getPub() - average);
        }
    }
    ofs << "Yvelaze axlos yvela bakalavris sashualo shefasebastan:\n\n";
    ofs << arr[index];
    ofs << "--------------------" << endl;
    ofs.close();
}

const string& HeightSchool::getPub()const noexcept{ return name; }

const string& HeightSchool::getPub()const noexcept;