Input and Output in C++

Input and output are the most basic forms of communication between a program and the user. C++ provides a simple and powerful way to display information on the screen and receive data from the keyboard using the iostream library.

The iostream Library

To use input and output in C++, include the <iostream> header file at the top of the program. This file provides two main objects:

• cout — Used to output (print) data to the console.
• cin — Used to input (read) data from the keyboard.

Output Using cout

cout stands for character output. The << operator (called the insertion operator) is used to send data to the output.

#include <iostream>
using namespace std;

int main() {
    cout << "Hello, World!";
    return 0;
}

Output:

Hello, World!

Printing Multiple Items:

int age = 20;
string name = "Raj";
cout << "Name: " << name << ", Age: " << age << endl;

Output:

Name: Raj, Age: 20

New Line — endl vs

Both endl and move the output to a new line. The difference is:

• endl — Moves to new line AND flushes the output buffer (slightly slower).
• — Just moves to a new line (faster, preferred in loops).

cout << "Line 1" << endl;
cout << "Line 2" << "
";
cout << "Line 3
";

Output:

Line 1
Line 2
Line 3

Input Using cin

cin stands for character input. The >> operator (extraction operator) reads data from the keyboard and stores it in a variable.

#include <iostream>
using namespace std;

int main() {
    int number;
    cout << "Enter a number: ";
    cin >> number;
    cout << "You entered: " << number << endl;
    return 0;
}

Sample Run:

Enter a number: 42
You entered: 42

Reading Multiple Inputs

#include <iostream>
using namespace std;

int main() {
    int a, b;
    cout << "Enter two numbers: ";
    cin >> a >> b;
    cout << "Sum = " << a + b << endl;
    return 0;
}

Sample Run:

Enter two numbers: 5 7
Sum = 12

Reading Strings with cin

When using cin to read a string, it reads only up to the first space. For reading a full line (including spaces), use getline().

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

int main() {
    string fullName;
    cout << "Enter your full name: ";
    getline(cin, fullName);
    cout << "Hello, " << fullName << "!" << endl;
    return 0;
}

Sample Run:

Enter your full name: Priya Sharma
Hello, Priya Sharma!

Formatting Output with setw and fixed

For formatted output (like aligning columns or controlling decimal places), include <iomanip>:

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

int main() {
    double price = 49.9;
    cout << fixed << setprecision(2);
    cout << "Price: " << price << endl;
    return 0;
}

Output:

Price: 49.90

Escape Sequences

Escape sequences are special characters that start with a backslash \ and produce formatting effects in output:

cout << "Name:	Alice
";
cout << "She said: "Hello!"" << endl;

Output:

Name:	Alice
She said: "Hello!"

A Complete Input/Output Example

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

int main() {
    string name;
    int age;

    cout << "Enter your name: ";
    cin >> name;
    cout << "Enter your age: ";
    cin >> age;

    cout << "
--- Profile ---
";
    cout << "Name : " << name << "
";
    cout << "Age  : " << age  << "
";
    return 0;
}

Sample Run:

Enter your name: Sam
Enter your age: 22

--- Profile ---
Name : Sam
Age  : 22

Key Takeaways

• cout << is used to print output to the screen.
• cin >> is used to read input from the keyboard.
• endl and both add a new line; is faster.
• Use getline() to read a full line of text including spaces.
• Escape sequences like and control text formatting.