Files & Streams

#include <iostream>
#include <fstream>   // file streams live here: ofstream, ifstream, fstream
using namespace std;

int main() {
    // ofstream = "output file stream" -> opens a file for WRITING.
    // If the file does not exist it is created; if it exists it is OVERWRITTEN.
    ofstream out("scores.txt");

    // ALWAYS check the file actually opened before you use it.
    if (!out.is_open()) {
        cout << "Could not open scores.txt for writing" << endl;
        return 1;               
...

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

int main() {
    // ifstream = "input file stream" -> opens a file for READING.
    ifstream in("scores.txt");

    if (!in.is_open()) {
        cout << "scores.txt not found" << endl;
        return 1;
    }

    // Pattern 1: read WHOLE LINES with getline.
    // getline(stream, line) returns the stream, which is "false" at end-of-file,
    // so the loop stops automatically when there is nothing left to read.
    s
...

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

struct Point { int x; int y; };   // a fixed-size record (8 bytes here)

int main() {
    // ios::app  -> APPEND. Writes go to the END; existing content is kept.
    ofstream log("log.txt", ios::app);
    log << "user logged in" << endl;   // added after whatever was already there
    log.close();

    // ios::binary -> write RAW BYTES, no text formatting / newline translation.
    Point p{3, 4};
    ofstream bout("point.bin", ios::bin
...

#include <iostream>
#include <sstream>   // istringstream = "read a string as if it were a file"
#include <string>
using namespace std;

int main() {
    // 🎯 YOUR TURN — fill in the blanks marked ___ then press "Try it Yourself".
    // No real file needed: istringstream lets us PRACTISE parsing in memory.

    string csv = "Alice,London,30";

    // istringstream wraps the string so we can use getline / >> on it.
    istringstream iss(csv);

    string name, city, ageText;

    // getline(str
...

#include <iostream>
#include <sstream>   // ostringstream builds a string; istringstream reads one
#include <string>
#include <vector>
using namespace std;

int main() {
    // 🎯 YOUR TURN — parse some numbers, then BUILD a report string.

    string data = "10 25 5";        // three numbers separated by spaces
    istringstream in(data);

    // Read tokens with >> (it splits on whitespace for you).
    int total = 0, n;
    vector<int> nums;
    while (in >> n) {
        nums.push_back(n);
  
...