Practice Questions — File Handling (ifstream, ofstream, fstream)

#include <iostream>
#include <fstream>
#include <map>
#include <string>
using namespace std;

int main() {
    ofstream out("text.txt");
    out << "the cat sat on the mat the cat";
    out.close();

    ifstream in("text.txt");
    map<string, int> freq;
    string word;
    while (in >> word) freq[word]++;
    in.close();

    for (auto& [w, c] : freq)
        cout << w << ": " << c << endl;
    return 0;
}

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
using namespace std;

int main() {
    ofstream out("marks.csv");
    out << "Arjun,85,90,78" << endl;
    out << "Priya,92,88,95" << endl;
    out << "Kiran,78,82,80" << endl;
    out.close();

    ifstream in("marks.csv");
    string line, topperName;
    int topperTotal = 0;

    while (getline(in, line)) {
        stringstream ss(line);
        string name, token;
        getline(ss, name, ',');
        int total = 0;
        while (getline(ss, token, ','))
            total += stoi(token);
        cout << name << ": Total=" << total << endl;
        if (total > topperTotal) {
            topperTotal = total;
            topperName = name;
        }
    }
    cout << "Topper: " << topperName << " (" << topperTotal << ")" << endl;
    in.close();
    return 0;
}

#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;

struct Student {
    int rollNo;
    char name[30];
    double marks;
};

void addStudent(const string& fname, int roll, const char* name, double marks) {
    Student s;
    s.rollNo = roll;
    strcpy(s.name, name);
    s.marks = marks;
    ofstream file(fname, ios::binary | ios::app);
    file.write(reinterpret_cast<char*>(&s), sizeof(Student));
    file.close();
}

void updateMarks(const string& fname, int roll, double newMarks) {
    fstream file(fname, ios::in | ios::out | ios::binary);
    Student s;
    while (file.read(reinterpret_cast<char*>(&s), sizeof(Student))) {
        if (s.rollNo == roll) {
            s.marks = newMarks;
            file.seekp(-static_cast<int>(sizeof(Student)), ios::cur);
            file.write(reinterpret_cast<char*>(&s), sizeof(Student));
            break;
        }
    }
    file.close();
}

void displayAll(const string& fname) {
    ifstream file(fname, ios::binary);
    Student s;
    while (file.read(reinterpret_cast<char*>(&s), sizeof(Student)))
        cout << s.rollNo << ": " << s.name << ", Marks: " << s.marks << endl;
    file.close();
}

int main() {
    string fname = "students.dat";
    ofstream clear(fname, ios::trunc); clear.close();

    addStudent(fname, 101, "Arjun", 85);
    addStudent(fname, 102, "Priya", 78);
    updateMarks(fname, 102, 95);
    displayAll(fname);
    return 0;
}

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <map>
using namespace std;

class Config {
    map<string, string> data;
public:
    void load(const string& filename) {
        ifstream file(filename);
        string line;
        while (getline(file, line)) {
            if (line.empty() || line[0] == '#') continue;
            size_t pos = line.find('=');
            if (pos != string::npos)
                data[line.substr(0, pos)] = line.substr(pos + 1);
        }
        file.close();
    }
    string get(const string& key, const string& defaultVal = "") {
        auto it = data.find(key);
        return it != data.end() ? it->second : defaultVal;
    }
    void display() {
        for (auto& [k, v] : data) cout << k << " = " << v << endl;
    }
};

int main() {
    ofstream out("app.conf");
    out << "# Config file" << endl;
    out << "host=localhost" << endl;
    out << "port=3306" << endl;
    out << "debug=true" << endl;
    out.close();

    Config config;
    config.load("app.conf");
    config.display();
    cout << "timeout = " << config.get("timeout", "30") << " (default)" << endl;
    return 0;
}

#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#include <string>
using namespace std;

struct Player {
    string name;
    int score;
};

void addScore(const string& fname, const string& name, int score) {
    ofstream file(fname, ios::app);
    file << name << " " << score << endl;
    file.close();
}

vector<Player> loadScores(const string& fname) {
    vector<Player> players;
    ifstream file(fname);
    string name;
    int score;
    while (file >> name >> score)
        players.push_back({name, score});
    file.close();
    return players;
}

void showTop(const string& fname, int n) {
    auto players = loadScores(fname);
    sort(players.begin(), players.end(),
        [](const Player& a, const Player& b) { return a.score > b.score; });
    cout << "=== Top " << n << " ===" << endl;
    for (int i = 0; i < min(n, (int)players.size()); i++)
        cout << i + 1 << ". " << players[i].name << ": " << players[i].score << endl;
}

int main() {
    string fname = "leaderboard.txt";
    ofstream clear(fname, ios::trunc); clear.close();

    addScore(fname, "Arjun", 850);
    addScore(fname, "Priya", 920);
    addScore(fname, "Kiran", 780);
    addScore(fname, "Neha", 920);
    showTop(fname, 3);
    return 0;
}