재귀 클래스, 클래스 함수 재귀에 관해 질문 드립니다.

class Student {
public :
    Student() {}
    Student(string name, string address, string phone_number) {
        student_name = name;
        student_address = address;
        student_phone_number = phone_number;
    }
 
    string getName()                         { return student_name ; }
    void setName(string name)                { student_name = name; }
    string getAddress()                      { return student_address; }
    void setAddress(string address)          { student_address = address; }
    string getPhoneNumber()                  { return student_phone_number; }
    void setPhoneNumber(string phone_number) { student_phone_number = phone_number; }
 
    bool operator==(const Student &students);
 
    bool make_friends(const Student &students);
    void display_friends();
    <span>void make_connection();</span>
    void display_connection();
    vector<Student> connection;
private :
    string student_name;
    string student_address;
    string student_phone_number;
    vector<Student> friends;
    void sort_friends();
};

void Student::make_connection() {
    unsigned int i, j, k;
    for(i = 0; i < friends.size(); i++) {
<span>//        cout << friends[i].getName() << endl;</span>
<span>        friends<span>.make_connection();</span>
[i]//        cout << friends[i].getName() << endl;</span>
        // 기존의 친구들의 목록을 더한다. 
        if(connection.empty())
            connection.push_back(friends[i]);
        else {
            for(j = 1; j < connection.size(); j++) {
                if(friends[i] == connection[j]) {
                    break;
                }
            }
            if((j-1) == connection.size())
                connection.push_back(friends[i]);
        }
 
<span>        // 자신의 연락망에 친구들의 연락망을 참조해 추가한다. 
        cout << friends[i].connection.size() << endl;
        for(j = 0; j < friends[i].connection.size(); j++) {
            cout << friends.size() << endl;
            // 친구의 연락망 중 자신의 연락망과 중복된 것이 없는지 확인한다. 
            for(k = 0; k < connection.size(); k++)
                if(friends[i].connection[j] == connection[k]) {
                    break;
                }
            if((k-1) != connection.size())
                connection.push_back(friends[i].connection[j]);
        }</span>
    }
}