Cin and Cout in C+ with example

C++ utilizes the concept of streams to perform input and output operations. A stream is a sequence of bytes in which character sequences are flown into or flowed out of. Streams operate as intermediates between the program and the I/O devices, helping programmers achieve device-independent I/O operations. The two types of streams in C++ are:

• Input stream
• Output stream

Header Files for Input/Output Operations:

• <iostream>: Stands for standard input-output stream. This header file contains definitions for objects like cin, cout, cerr, etc.
• <iomanip>: Stands for input-output manipulators. The methods declared in this file are used for manipulating streams and contain definitions of functions like setw, setprecision, etc.
• <fstream>: Describes the file stream and is used to handle data being read from a file as input or being written into a file as output.

The objects discussed in this article are cin and cout, which are the most commonly used objects for taking inputs and printing outputs.

Standard Output Stream (cout)

cout is an object of the ostream class. The standard output device is the display screen. Characters are inserted into the output stream using the insertion operator (<<). Multiple insertion operations can be chained in a single statement.

#include <iostream>
using namespace std;

int main() {
    int Hello = 10;

    cout << "Hello";    // Prints the text "Hello" on the display screen.
    cout << Hello;       // Prints the contents of the variable 'Hello' (10) on the screen.
    cout << 10;          // Prints number 10 on the screen.

    // Chaining multiple insertions
    cout << "Welcome" << " to" << " OpenGenus!";

    return 0;
}

Chaining multiple insertions is useful to mix literals and variables in a single statement.

cout << "My name is " << name << " and I am " << age << " years old";

To add a line break, the newline character ('\n') or the endl manipulator can be used.

cout << "This is sentence 1.\n";
cout << "This is sentence 2.";

Formatting the output is done through the use of I/O manipulators. Examples include:

• setw(): Sets the width of the field assigned for the output.
• setprecision(): Sets the total number of digits to be displayed when floating-point numbers are printed.

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

int main() {
    cout << setw(6) << "X";  // Output: _ _ _ _ _ X

    // Using setprecision
    cout << setprecision(5) << 22.0 / 7;  // Output: 3.1415

    return 0;
}

Standard Input Stream (cin)

cin is an object of the istream class. The standard input device is the keyboard. The extraction operator (>>) is used with cin to extract values from the stream.

#include <iostream>
using namespace std;

int main() {
    int x, y;
    cout << "Enter two integers separated by space: ";
    cin >> x >> y;
    cout << "Sum: " << x + y;

    return 0;
}

Using cin with strings requires special attention due to whitespace being considered as a terminating character. The getline() function is often used to read complete lines.

#include <iostream>
using namespace std;

int main() {
    string myName;
    cout << "Enter your name: ";
    getline(cin, myName);
    cout << "Welcome " << myName;

    return 0;
}

Another way to use getline with cin is:

char address[20];
cout << "Address: ";
cin.getline(address, 20);
cout << "You live in " << address;

In summary, cin and cout are essential for input and output operations in C++, providing a flexible and powerful way to interact with the user and display information.