Mini Project: Student Manager - Part 3

Let's Think About This For a Second

Part 3 is the final stage of the project, where we'll polish the program to near-production quality. First, we'll add try/catch exception handling so the program doesn't crash if non-numeric input is entered for marks. Second, we'll use the algorithm library's sort() to sort the student list by marks. Finally, we'll use fstream to save student data into a students.txt file, and set things up so that when the program reopens, it can read the data back in (persistence). This is where the file handling topic gets put to real use in a practical project.

Let's Build It

In addStudent(), after reading marks with cin >> marks;, throw an exception if cin.fail() happens, and show an error message with a try/catch block. Build a sortByMarks(vector<Student>& students) function that uses std::sort() with the lambda comparator [](const Student& a, const Student& b){ return a.getMarks() > b.getMarks(); }. In saveToFile(const vector<Student>& students), open an ofstream and write each student's data as a line in a text file. In loadFromFile(vector<Student>& students), open an ifstream, read the file line by line if it exists, and refill the vector — call this function at the start of main() when the program launches. Add Sort by Marks and Save & Exit options to the menu.

• Entering invalid marks input no longer crashes the program — try/catch shows an error message instead
• Can sort the student list by marks using std::sort() with a lambda comparator
• Data no longer gets lost between program runs — save/load works with ofstream/ifstream to students.txt

Example Code

#include <fstream>
#include <algorithm>
#include <stdexcept>

void sortByMarks(vector<Student>& students) {
    sort(students.begin(), students.end(),
        [](const Student& a, const Student& b) {
            return a.getMarks() > b.getMarks();
        });
    cout << "Sorted by marks (highest first).\n";
}

void saveToFile(const vector<Student>& students) {
    ofstream fout("students.txt");
    for (const Student& s : students) {
        fout << s.getRoll() << " " << s.getName() << " " << s.getMarks() << "\n";
    }
    fout.close();
    cout << "Saved to students.txt\n";
}

void loadFromFile(vector<Student>& students) {
    ifstream fin("students.txt");
    if (!fin) return;

    int roll;
    string name;
    double marks;
    while (fin >> roll >> name >> marks) {
        students.push_back(Student(name, roll, marks));
    }
    fin.close();
}

void addStudentSafe(vector<Student>& students) {
    try {
        string name;
        int roll;
        double marks;
        cout << "Enter name: ";
        cin >> name;
        cout << "Enter roll: ";
        cin >> roll;
        cout << "Enter marks: ";
        cin >> marks;

        if (cin.fail()) {
            throw runtime_error("Invalid marks input!");
        }
        students.push_back(Student(name, roll, marks));
        cout << "Student added!\n";
    } catch (const runtime_error& e) {
        cout << "Error: " << e.what() << "\n";
        cin.clear();
    }
}

Running the program and choosing Save & Exit creates a students.txt file and writes the data into it; reopening the program brings back the previously saved student list.