cout in C++

cout is the standard output stream object in C++ used to display data on the screen. It is one of the most commonly used objects provided by the <iostream> library for producing console output.

Defined in the <iostream> header file.
Uses the insertion operator (<<) to send data to the output stream.
Supports output of different data types, including strings, characters, numbers, and expressions.
Can be combined with manipulators and member functions to control output formatting.

C++

#include <iostream>
using namespace std;

int main() {
    
  	// Print standard output
    // on the screen
    cout << "Welcome to GFG";

    return 0;
}

Output

Welcome to GFG

Explanation

cout sends the string "Welcome to GFG" to the standard output stream.
The insertion operator (<<) passes the data to cout.
The text is displayed on the console when the program executes.

Syntax

cout << var_name;

Where:

cout: It is the standard output stream object.
<<: It is the insertion operator used to insert data into cout.
var_name: It represents the variable or literal whose value you want to display.

Displaying Multiple Variables

In addition to displaying individual values, cout can output multiple variables and strings together in a single statement.

C++

#include <iostream>
using namespace std;

int main() {
    int n = 42;
    string s = "The answer is ";

  	// Printing both n and s
    cout << s << n;
  
    return 0;
}

Output

The answer is 42

Explanation

The string stored in s is displayed first using cout.
The value of n is printed immediately after the string in the same output statement.
The insertion operator (<<) is chained to display multiple values sequentially.
The output produced is: The answer is 42

Commonly Used cout Member Functions

The cout object provides several member functions that help control the formatting and display of output.

Member Function	Description
cout.put(char)	Writes a single character to the output stream.
*cout.write(char, int)**	Writes a block of characters from the array to the output stream.
cout.precision(int)	Sets the decimal precision for displaying floating-point numbers.
cout.setf(ios::fmtflags)	Sets the format flags for the stream.
cout.width(int)	Sets the minimum field width for the next output.
cout.fill(char)	Sets the fill character for padding the field.

The following example demonstrates how to output individual characters and character arrays using cout.put() and cout.write().

C++

#include <iostream>
using namespace std;

int main() {
    char s[] = "Welcome at GFG";
    char c = 'e';

    // Print first 6 characters
    cout.write(s, 6);

    // Print the character c
    cout.put(c);
  
    return 0;
}

Output

Welcome

Explanation

cout.write(s, 6) prints the first 6 characters of the character array.
cout.put(c) outputs the character stored in c.
These functions provide more control over output than the insertion operator.

C++ program to illustrate the use of cout.precision():

C++

#include <iostream>
using namespace std;

int main() {
    double pi = 3.14159783;

    // Set precision to 5
    cout.precision(5);

    cout << pi << endl;

    // Set precision to 7
    cout.precision(7);

    cout << pi << endl;

    return 0;
}

Output

3.1416
3.141598

Explanation

cout.precision(5) sets the output precision to 5 significant digits.
cout.precision(7) increases the precision to 7 significant digits.
This function is useful when displaying floating-point values with controlled accuracy.

Syntax

Displaying Multiple Variables

Commonly Used cout Member Functions

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