C++ iostream

iostream Components

cout << "Hello!" << endl;

int age;
cin >> age;

cerr << "Error occurred!" << endl;

clog << "Log message" << endl;

🔹 Basic Output with cout

The cout object, part of the standard output stream, is the primary tool for displaying information to the console in C++. Used with the insertion operator (<<), it can output literals, variables, and expressions, and supports chaining multiple items in a single statement. It's essential for debugging, providing user feedback, and presenting program results. For more complex formatting, manipulators like endl (to insert a newline and flush the buffer) or functions from the <iomanip> library can be used with cout to control the appearance of text, numbers, and spacing.

#include <iostream>
using namespace std;

int main() {
    // Simple output
    cout << "Welcome to C++!" << endl;
    
    // Multiple values
    int age = 25;
    string name = "Alice";
    cout << "Name: " << name << ", Age: " << age << endl;
    
    // Without endl (no new line)
    cout << "Hello ";
    cout << "World!";
    cout << endl;
    
    // Using \n instead of endl
    cout << "Line 1\nLine 2\nLine 3" << endl;
    
    return 0;
}

🔹 Basic Input with cin

The cin object, tied to the standard input stream, reads user-provided data from the keyboard during program execution. It uses the extraction operator (>>), which automatically skips leading whitespace and reads data based on the variable's type. However, it stops reading at the next whitespace character. For robust input, especially when expecting multiple words or handling potential errors, it's often combined with methods like getline() or checked with conditional statements to verify the input operation succeeded and clear the input buffer if needed.

#include <iostream>
using namespace std;

int main() {
    string name;
    int age;
    double salary;
    
    // Getting user input
    cout << "Enter your name: ";
    cin >> name;
    
    cout << "Enter your age: ";
    cin >> age;
    
    cout << "Enter your salary: ";
    cin >> salary;
    
    // Display the input
    cout << "\n--- Your Information ---" << endl;
    cout << "Name: " << name << endl;
    cout << "Age: " << age << " years" << endl;
    cout << "Salary: $" << salary << endl;
    
    return 0;
}

🔹 Reading Strings with Spaces

To read entire lines of text including spaces, the getline() function is indispensable, as cin >> stops at whitespace. The standard syntax getline(cin, stringVariable) reads from the input stream until it encounters a newline character, storing the result in a string object. This is crucial for reading full names, addresses, sentences, or any multi-word user input. It's important to manage the input buffer correctly; sometimes a preceding cin >> operation leaves a newline in the buffer, which requires using cin.ignore() before getline() to get the intended input.

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

int main() {
    string fullName;
    string address;
    
    cout << "Enter your full name: ";
    getline(cin, fullName);
    
    cout << "Enter your address: ";
    getline(cin, address);
    
    cout << "\nYour Details:" << endl;
    cout << "Full Name: " << fullName << endl;
    cout << "Address: " << address << endl;
    
    return 0;
}

🔹 Formatting Output

Advanced output formatting in C++ is controlled using manipulators from the <iomanip> and <iostream> libraries, allowing precise control over presentation. Common manipulators include setprecision(n) for decimal places, fixed for fixed-point notation, setw(n) to set field width, and left/right for alignment. These tools are essential for creating professional, readable output such as formatted tables, aligned columns of numbers, financial reports with consistent decimal places, or scientific data displayed with specific precision, ensuring the output is both user-friendly and publication-ready.

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

int main() {
    double pi = 3.14159265;
    int number = 42;
    
    // Set decimal precision
    cout << "Pi with 2 decimals: " << fixed << setprecision(2) << pi << endl;
    cout << "Pi with 4 decimals: " << fixed << setprecision(4) << pi << endl;
    
    // Set field width
    cout << "Number with width 10: " << setw(10) << number << endl;
    cout << "Number with width 10 (left): " << left << setw(10) << number << "|" << endl;
    
    // Fill with characters
    cout << "Number with zeros: " << setfill('0') << setw(5) << number << endl;
    
    return 0;
}