Dancho

#include <iostream>
#include <string>
#include <fstream>
#include <vector>
#include <conio.h>

using namespace std;

struct Student {
    string name;
    string egn;

    double physics;
    double maths;
    double c_science;
};

void create_file(fstream &, const string);
void add_students(fstream &, Student[], size_t &);
void read_students(fstream &, Student[], size_t);
double average_grade_at_physics(fstream &, Student [], size_t);

int main() {
    fstream file;
    Student students[30];

    size_t choice, size = 0;

    do {
        system("cls");
        cout << "Menu: \n";
        cout << "[1] Create empty file\n";
        cout << "[2] Add students to file\n";
        cout << "[3] Edit students information\n";
        cout << "[4] Average grade in physics where maths exam is passed\n\n";
        cout << "[0] Exit\n\n";
        cout << "Your choice: ";
        cin >> choice;

        switch (choice) {
            case 1:
                system("cls");

                create_file(file, "students.dat");

                cout << "File created! Press any key to return to the menu...";
                _getch();
                break;

            case 2:
                system("cls");

                add_students(file, students, size);
                break;

            case 3:
                system("cls");

                read_students(file, students, size);

                cout << "\n\nPress any key to return to the menu...";
                _getch();
                break;
            case 4:
                system("cls");

                cout << "The average grade of all students which have passed the maths exam is: " << average_grade_at_physics(file, students, size);

                cout << "\n\nPress any key to return to the menu...";
                _getch();
                break;
        }
    } while (choice != 0);


    return 0;
}

void create_file(fstream &file, const string filename) {
    file.open(filename, ios::binary | ios::out);
    file.close();
}

void add_students(fstream &file, Student student[], size_t &size) {
    size_t counter = 0;
    char answer;
    bool Running = true;

    file.open("students.dat", ios::binary | ios::app);

    while (Running) {
        cout << "Enter student's name: ";
        cin >> student[counter].name;

        cout << "Enter student's EGN: ";
        cin >> student[counter].egn;

        cout << "Enter student's grade at physics: ";
        cin >> student[counter].physics;

        cout << "Enter student's grade at maths: ";
        cin >> student[counter].maths;
        cout << "Enter student's grade at computer science: ";
        cin >> student[counter].c_science;

        cout << "Do you want to continue adding students? (y - yes / n - no)";
        cin >> answer;

        if (toupper(answer) == 'N') {
            Running = !Running;
        }
        counter++;

    }

    size = counter;

    file.write((char *)&student, sizeof(student));
    file.close();
}

void read_students(fstream &file, Student student[], size_t size) {

    string egn;

    file.open("students.dat", ios::in | ios::ate | ios::binary);
    file.read(reinterpret_cast<char *> (&student), sizeof(student));

    Student new_student;

    cout << "Enter student egn to search: ";
    cin >> egn;

    for (size_t i = 0; i < size; i++) {
        if (strcmp(egn.c_str(), student[i].egn.c_str())) {
            file.seekg( ( sizeof(student) ), ios::cur);

            cout << "Enter name for student with egn " << student[i].egn << " :";
            cin >> new_student.name;

            cout << "Enter physics grade for student with egn " << student[i].egn << " :";
            cin >> new_student.physics;

            cout << "Enter maths grade for student with egn " << student[i].egn << " :";
            cin >> new_student.maths;

            cout << "Enter computer science grade for student with egn " << student[i].egn << " :";
            cin >> new_student.c_science;

            file.write(reinterpret_cast<char *> (&student), sizeof(student));
        }
    }



    file.close();
}

double average_grade_at_physics(fstream &file, Student student[], size_t size) {

    size_t counter = 0;
    double average_grade = 0.0;

    file.open("students.dat", ios::binary | ios::in);
    file.read(reinterpret_cast<char *> (&student), sizeof(student));

    for (size_t i = 0; i < size; i++) {
        if (student[i].maths > 2) {
            average_grade += student[i].physics;
            counter++;
        }
    }

    file.close();

    return (average_grade / counter);
}