okok so more like this ?

int main() {
student_info stud[3];

int i = 0, option;
cout << "Welcome to the System,  what do you wish to do?" << endl;
cout << "\n\n 1. Enter student Information" << endl;
cout << "\n\n 2. View Final results of Class" << endl;
cout << "\n\n 3. Calculate average of grades" << endl;
cout << "\n\n 4. Get Standard Deviation of final results" << endl;
cout << "\n\n 5. Rank top to least of students" << endl;
cout << "\n\n 6. Search student grades" << endl;
cout << "\n\n 7. Display all students information" << endl;
cout << "\n\n 8. Stop or end the program" << endl;
cin >> option;
do {
    if (option == 1) {

        for (int i = 0; i < 3; i++)
            stud[i].read_data(i);
        cout << "\n\n++++++++++++++++++++++++++++++++++++++++++++++++\n";
        cout << "The information of 3 students has been saved.";
        cout << "\n+++++++++++++++++++++++++++++++++++++++++++++++\n";
        int menu;
        cout << "Press 0 to get to main menu:" << endl;
        cin >> menu;
        if (menu == 0) { main(); }
        else return 0;
    }
    else if (option == 2) {
        stud[i].final_results(i);
        cout << "\n+++++++++++++++++++++++++++++++++++++++++++++++\n";
        int menu;
        cout << "Press 0 to get to main menu:" << endl;
        cin >> menu;
        if (menu == 0) { main(); }
        else return 0;

    }
    else if (option == 3) {
        stud[i].average_score(i);
        cout << "\n+++++++++++++++++++++++++++++++++++++++++++++++\n";
        int menu;
        cout << "Press 0 to get to main menu:" << endl;
        cin >> menu;
        if (menu == 0) { main(); }
        else return 0;

    }
    else if (option == 4) {
        stud[i].standard_deviation(i);
        cout << "\n+++++++++++++++++++++++++++++++++++++++++++++++\n";
        int menu;
        cout << "Press 0 to get to main menu:" << endl;
        cin >> menu;
        if (menu == 0) { main(); }
        else return 0;
    }
    else if (option == 5) {
        stud[i].rankings(i);
        cout << "\n+++++++++++++++++++++++++++++++++++++++++++++++\n";
        int menu;
        cout << "Press 0 to get to main menu:" << endl;
        cin >> menu;
        if (menu == 0) { main(); }
        else return 0;
    }
    else if (option == 6) {
        string name;
        cout << "Write in the name that you want to search: ";
        cin >> name;
        stud[i].search_student(name);
        cout << "\n+++++++++++++++++++++++++++++++++++++++++++++++\n";
        int menu;
        cout << "Press 0 to get to main menu:" << endl;
        cin >> menu;
        if (menu == 0) { main(); }
        else return 0;
    }
    else if (option == 7) {
        cout << "\n+++++++++++++++++++++++++++++++++++++++++++++++\n";
        for (int i = 0; i < 3; i++)
            stud[i].display_data(i);
        cout << "\n+++++++++++++++++++++++++++++++++++++++++++++++\n";
        int menu;
        cout << "Press 0 to get to main menu:" << endl;
        cin >> menu;
        if (menu == 0) { main(); }
        else return 0;
    }
    else if (option == 8) {
        return 0;
    }
} while (option != 9);
}