Input, Output, and Formatting

#include <iostream>
using namespace std;

int main() {
    // Output chaining
    int a = 10, b = 20;
    cout << "a = " << a << ", b = " << b << endl;

    // Input chaining
    int x, y, z;
    cout << "Enter three numbers: ";
    cin >> x >> y >> z;
    cout << "Sum: " << x + y + z << endl;

    // Multiple types in one chain
    string name;
    int age;
    cout << "Enter name and age: ";
    cin >> name >> age;
    cout << name << " is " << age << " years old." << endl;

    return 0;
}

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

int main() {
    int rollNo;
    string fullName;

    cout << "Enter roll number: ";
    cin >> rollNo;

    // WRONG: getline reads the leftover '\n' from cin >>
    // getline(cin, fullName);  // fullName would be empty!

    // FIX: ignore the leftover newline
    cin.ignore();  // Discard the '\n' left by cin >>

    cout << "Enter full name: ";
    getline(cin, fullName);

    cout << "Roll: " << rollNo << endl;
    cout << "Name: " << fullName << endl;

    // Reading multiple lines
    string line1, line2;
    cout << "Enter address (2 lines):" << endl;
    getline(cin, line1);
    getline(cin, line2);
    cout << "Line 1: " << line1 << endl;
    cout << "Line 2: " << line2 << endl;

    return 0;
}

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

int main() {
    // setprecision without fixed: total significant digits
    double pi = 3.141592653589793;
    cout << "Default: " << pi << endl;
    cout << "setprecision(3): " << setprecision(3) << pi << endl;
    cout << "setprecision(10): " << setprecision(10) << pi << endl;

    // fixed + setprecision: decimal places
    cout << fixed;
    cout << "fixed + setprecision(2): " << setprecision(2) << pi << endl;
    cout << "fixed + setprecision(6): " << setprecision(6) << pi << endl;

    // Reset to default
    cout << defaultfloat;

    // setw and alignment
    cout << "\n--- Table ---" << endl;
    cout << left << setw(15) << "Name" << right << setw(10) << "Marks" << endl;
    cout << left << setw(15) << "Ananya" << right << setw(10) << 95 << endl;
    cout << left << setw(15) << "Vikram" << right << setw(10) << 87 << endl;
    cout << left << setw(15) << "Deepa" << right << setw(10) << 92 << endl;

    // setfill for zero-padding
    cout << "\n--- Zero Padding ---" << endl;
    for (int i = 1; i <= 5; i++) {
        cout << "Item " << setfill('0') << setw(3) << i << endl;
    }

    return 0;
}

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

int main() {
    const int N = 100000;

    // Timing with endl
    auto start1 = chrono::high_resolution_clock::now();
    for (int i = 0; i < N; i++) {
        cout << i << endl;  // Flushes every iteration
    }
    auto end1 = chrono::high_resolution_clock::now();

    // Timing with '\n'
    auto start2 = chrono::high_resolution_clock::now();
    for (int i = 0; i < N; i++) {
        cout << i << '\n';  // No flush
    }
    auto end2 = chrono::high_resolution_clock::now();

    auto ms1 = chrono::duration_cast<chrono::milliseconds>(end1 - start1).count();
    auto ms2 = chrono::duration_cast<chrono::milliseconds>(end2 - start2).count();

    cerr << "endl: " << ms1 << " ms" << endl;
    cerr << "'\\n': " << ms2 << " ms" << endl;

    return 0;
}

#include <iostream>
using namespace std;

int main() {
    // cout: standard output (buffered)
    cout << "This goes to stdout" << endl;

    // cerr: standard error (unbuffered) -- appears immediately
    cerr << "Error: something went wrong!" << endl;

    // clog: standard log (buffered)
    clog << "Log: program started" << endl;

    // In competitive programming, use cerr for debugging
    // The judge only checks stdout (cout)
    int arr[] = {3, 1, 4, 1, 5};
    int n = 5;
    cerr << "DEBUG: array = ";
    for (int i = 0; i < n; i++) cerr << arr[i] << " ";
    cerr << endl;

    // Your actual answer
    int sum = 0;
    for (int i = 0; i < n; i++) sum += arr[i];
    cout << sum << endl;  // Only this is checked by the judge

    return 0;
}

#include <iostream>
using namespace std;

int main() {
    // Fast I/O: must be the first two lines
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    // After these lines, do NOT use printf/scanf
    // Do NOT use endl -- use '\n'

    int t;
    cin >> t;
    while (t--) {
        int n;
        cin >> n;
        long long sum = 0;
        for (int i = 0; i < n; i++) {
            int x;
            cin >> x;
            sum += x;
        }
        cout << sum << '\n';
    }

    return 0;
}

#include <cstdio>
using namespace std;

int main() {
    // printf with format specifiers
    int age = 20;
    double gpa = 8.75;
    char grade = 'A';

    printf("Age: %d\n", age);
    printf("GPA: %.2f\n", gpa);    // 2 decimal places
    printf("Grade: %c\n", grade);

    // Formatted table with printf
    printf("\n%-15s %5s %10s\n", "Name", "Roll", "Marks");
    printf("%-15s %5d %10.1f\n", "Arjun", 101, 92.5);
    printf("%-15s %5d %10.1f\n", "Kavitha", 102, 88.0);
    printf("%-15s %5d %10.1f\n", "Ravi", 103, 95.3);

    // scanf for input
    int x;
    printf("\nEnter a number: ");
    scanf("%d", &x);  // Note the & (address-of operator)
    printf("You entered: %d\n", x);

    // Zero-padding with printf
    for (int i = 1; i <= 5; i++) {
        printf("Item %03d\n", i);  // 3-digit zero-padded
    }

    return 0;
}